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Neurology
Protocol
High-definition transcranial infraslow pink noise stimulation for chronic low back pain: protocol for a pilot, safety and feasibility randomised placebo-controlled trial
  1. Divya Bharatkumar Adhia1,
  2. Ramakrishnan Mani2,
  3. John N J Reynolds3,
  4. Sven Vanneste4,
  5. Dirk De Ridder1
  1. 1Department of Surgical Sciences, and Pain@Otago Research Theme, University of Otago - Dunedin Campus, Dunedin, New Zealand
  2. 2Centre for Health, Activity and Rehabilitation Research, School of Physiotherapy, and Pain@Otago Research Theme, University of Otago - Dunedin Campus, Dunedin, New Zealand
  3. 3Department of Anatomy and the Brain Health Research Centre, University of Otago - Dunedin Campus, Dunedin, New Zealand
  4. 4School of Psychology, Global Brain Health Institute, Institute of Neuroscience, Trinity College Dublin, Dublin, Ireland
  1. Correspondence to Dr Divya Bharatkumar Adhia; divya.adhia{at}otago.ac.nz

Abstract

Introduction Chronic low back pain (CLBP) is a common disabling health condition. Current treatments demonstrate modest effects, warranting newer therapies. Brain imaging demonstrates altered electrical activities in cortical areas responsible for pain modulation, emotional and sensory components of pain experience. Treatments targeting to change electrical activities of these key brain regions may produce clinical benefits. This pilot study aims to (1) evaluate feasibility, safety and acceptability of a novel neuromodulation technique, high-definition transcranial infraslow pink noise stimulation (HD-tIPNS), in people with CLBP, (2) explore the trend of effect of HD-tIPNS on pain and function, and (3) derive treatment estimates to support sample size calculation for a fully powered trial should trends of effectiveness be present.

Methods and analysis A pilot, triple-blinded randomised two-arm placebo-controlled parallel trial. Participants (n=40) with CLBP will be randomised to either sham stimulation or HD-tIPNS (targeting somatosensory cortex and dorsal and pregenual anterior cingulate cortex). Primary outcomes include feasibility and safety measures, and clinical outcomes of pain (Brief Pain Inventory) and disability (Roland-Morris disability questionnaire). Secondary measures include clinical, psychological, quantitative sensory testing and electroencephalography collected at baseline, immediately postintervention, and at 1-week, 1-month and 3 months postintervention. All data will be analysed descriptively. A nested qualitative study will assess participants perceptions about acceptability of intervention and analysed thematically.

Ethics and dissemination Ethical approval has been obtained from Health and Disability Ethics Committee (Ref:20/NTB/67). Findings will be reported to regulatory and funding bodies, presented at conferences, and published in a scientific journal.

Trial registration number ACTRN12620000505909p.

  • Back pain
  • Pain management
  • Neurology
  • Neurological pain
  • Spine
http://creativecommons.org/licenses/by-nc/4.0/

This is an open access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited, appropriate credit is given, any changes made indicated, and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/.

http://dx.doi.org/10.1136/bmjopen-2021-056842

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    Strengths and limitations of this study

    • This study will use a novel neuromodulation technique (high-definition transcranial infraslow pink noise stimulation) to simultaneously target cortical areas responsible for pain modulation, emotional and sensory components of pain experience.

    • The use of Starstim-Home transcranial electrical stimulation system allows appropriate blinding of the treating researcher, and the possibility of a high-quality triple-blinded (participant, treatment therapist and outcome assessor) randomised placebo-controlled trial.

    • Sample size estimation has not been conducted in this feasibility and safety study design.

    Introduction

    Chronic low back pain (CLBP) is a significant and growing health challenge, affecting individuals, the wider community and the healthcare system.1–3 Along with pain and impaired function, individuals with CLBP have significant psychological comorbidities and poor quality of life.1–3 Currently available treatments for CLBP demonstrate at best small effect sizes.4–6 Pharmacological interventions are not effective with a high risk of adverse outcomes.7–9 Thus, new, innovative, evidence-based, safer therapies are warranted for the management of CLBP.

    Resting-state cortical activity alterations have been demonstrated in individuals with CLBP.10–13 The most notably involved cortical areas include the anterior cingulate cortex (ACC) and the primary somatosensory cortex (SSC), which are the central hubs of the pain processing brain networks.10–18 The ACC, particularly the pregenual region (pgACC), is part of the descending pain modulatory system (or anti-nociceptive system), the activation of which releases μ-opioids that act to modulate incoming nociception information from the hyperactive, spinal cord circuits, thereby alleviating pain.13 16 17 19 20 The SSC, along with the dorsal region of ACC (dACC), is part of ascending nociceptive (lateral and medial) pathways that are responsible for encoding the sensory (ie, painfulness) and the emotional components (eg, suffering) of the pain experience.13 16 17 19 20 Recent evidence suggests that alterations in the functional connectivity patterns between the pain processing regions (pgACC, dACC, SSC) are critical for maintaining chronic pain and are associated with its clinical and psychological outcomes.14–16 21–28

    Neuromodulatory interventions targeted to alter activities in cortical pain processing areas may improve clinical outcomes. Transcranial electrical stimulation (TES), a non-invasive brain stimulation technique, can influence the electrical activity of targeted brain regions, promote cortical plasticity and improve the functional connectivity to/from the targeted area, thereby improving pain modulation. Recent systematic reviews and meta-analyses demonstrate positive effects of the TES techniques in chronic pain conditions (eg, fibromyaligia, migraine, spinal cord injury).29–32 However, the evidence for effect of TES for treatment of CLBP is limited (n=10 pilot studies,33–42 n=2 protocols43 44) and have demonstrated mixed results. Recent systematic reviews and meta-analyses suggests that there is very low-quality evidence that a single session of TES have short term effects for improving pain in people with CLBP.45 46 Previous TES studies targeted altering cortical electrical activity of a single superficial brain region33–36 38–42 (eg, Motor cortex or dorsolateral prefrontal cortex) using transcranial direct current stimulation (tDCS), except one study37 that targeted a deeper brain region (dACC). None of the studies has simultaneously targeted multiple-brain regions (pgACC, dACC, SSC) responsible for the descending and ascending modulation of nociceptive sensory information. Further, the stimulation technique used in the previous TCS studies involved applying two large scalp electrode pads that deliver currents to diffuse areas of the brain, making focalised stimulation of targeted brain regions less feasible. Focal and simultaneous stimulation of multiple brain regions could help improve clinical outcomes with larger effect sizes, similar to invasive neuromodulatory interventions.47

    We propose determining the feasibility and safety of a novel high-definition transcranial infraslow pink noise stimulation (HD-tIPNS) technique, targeting the pgACC, dACC and SSC regions simultaneously in people with CLBP. The HD-tIPNS technique was developed to specifically modulate the infraslow electrical activity (0.0–0.1 Hz) in the brain. The infraslow electrical activity, a fundamental frequency range of the brain, reorganises neurons and improves the electrical connectivity of the brain-wide functional networks.48–51 The infraslow frequency plays a profound role in modulating and synchronising high-frequency cortical activity that are known to be affected in chronic pain,50 52–54 and is also critically involved in mediating pain perception.55 Evidence from imaging studies also demonstarte alterations in the infraslow oscillations in individuals with CLBP in the pain processing brain regions (pgACC, dACC, SSC).56 57 The pink noise frequency spectrum resembles the naturally occurring signals in the self-organisation of the brain, thus can be more effective than standard tDCS electrical parameters used in previous studies.58 59 We, therefore, believe that specifically and simultaneously targeting the fundamental infraslow activity at key nodes of pain processing networks, using a novel HD-tIPNS technique, could normalise brain-wide electrical activity and functional connectivity between areas of interest, promoting better pain modulation and producing more meaningful clinical benefits. This protocol outlines the methods and analysis used in the pilot randomised controlled trial. The specific aims are to (1) evaluate the feasibility, safety and acceptability of the HD-tIPNS technique in people with CLBP, (2) explore the trend of effect of HD-tIPNS on pain and function, and (3) provide estimates of clinical outcome measures to support a sample size calculation for a fully powered trial should the trend of effectiveness be present.

    Methods and analysis

    The following guides have been used to prepare this study protocol: Standard Protocol Items: Recommendations for Interventional Trials statement,60 the template for intervention description and replication checklist61 and IMMPACT Recommendations.62–66 In addition, this trial has been prospectively registered (table 1).

    View this table:
    Table 1

    WHO trial registration data set (V.1.3.1)

    Study design

    The proposed study will be a triple blinded pilot randomised placebo-controlled parallel trial with two intervention arms. The outcome measures will be collected at baseline, immediately postintervention, and at follow-up periods: 1-week, 1-month and 3 months postintervention (figure 1).

    Figure 1
    Figure 1

    Study design and timelines. dACC, dorsal anterior cingulate cortex; EEG, electroencephalography; HD-tIPNS, high-definition transcranial infraslow pink noise stimulation; pgACC, pregenual anterior cingulate cortex; SSC, primary somatosensory cortex.

    Randomisation

    A research administrator, not involved in other procedures, will randomise participants on a 1:1 basis using a computerised open-access randomisation software programme to:

    • Group 1: HD-tIPNS.

    • Group 2: Sham stimulation.

    The randomisation schedule will be concealed in sequentially numbered, sealed opaque envelopes and provided to participants at their baseline measurements.

    Blinding

    Participants, outcome assessor, and treating researchers will be blinded to group allocation. Stimulation programmes on Starstim device will be designed and controlled by an independent researcher to allow blinding of the treating researcher. The success of blinding will be assessed after the completion of the intervention and follow-up phases. The participant, and the outcome assessor, and treating researcher will be asked ‘What type of treatment they believe that they/the participant received respectively?’ and will be required to choose between three options: active, sham or don’t know. The confidence in their judgement will also be assessed on an 11-point Numeric Rating Scale (NRS) (0=not at all confident to 10=extremely confident), with the reason for their judgement being noted and whether the intervention was revealed to them. Unblinding will be permissible only in the case of an adverse event or any unexpected event.

    Study setting

    This study will be conducted in the Department of Surgical Sciences laboratory, Dunedin School of Medicine, Dunedin hospital, New Zealand.

    Participants and eligibility criteria

    Adults with CLBP will be eligible to participate.

    Inclusion criteria

    Capable of understanding and signing an informed consent form, age between 18 and 75 years on the day of the consent, pain in the lower back (the region between 12th rib and gluteal fold) that occurs everyday for ≥3 months, a score of ≥4 on an 11-point Numeric Pain Rating Scale (NPRS, 0=no pain to 10=worst pain imaginable) in the past 4 weeks prior to enrolment, a disability score of ≥5 on Roland-Morris Disability Questionnaire.67 68 These cut-off scores are used as an indication that CLBP significantly impacts daily functioning, are by International Association of Study of Pain guidelines and are in line with optimal Delphi definitions of LBP prevalence.3 67–70

    Exclusion criteria

    Participants with the following self-reported health conditions will be excluded: Inflammatory arthritis, undergoing any therapy from a health professional (eg, physiotherapist or chiropractor), recent soft tissue injuries of the back in the last 3 months, history of surgery to the back region or waiting/scheduled for any procedures within the next 6 months, current intake of any centrally-acting medications or intention of taking new medications in the next 3 months, steroid injections to the back in past 6 months, radicular pain and radiculopathy, history of neurological diseases, unstable medical or psychiatric conditions, history of epilepsy or seizures, peripheral neuropathy, vascular disorders, substance abuse, dyslipidaemia, cognitive impairments (dementia, post-traumatic stress disorders, Alzheimer’s disease; assessed as a score of <24 on the Mini-Mental State Examination conducted at baseline), history of uncontrolled/untreated hypertension, presence of any pacemaker or defibrillator or electronic/metal body implants (around the head/neck region) and recent or current pregnancy.

    Sample size

    This proposed research is a pilot exploratory study, which will be executed to make a power estimate for a future phase II study should the intervention appear feasible, safe, acceptable and show trends of effectiveness. Hence a sample size calculation was not performed. Based on statistical advice, a sample of 40 participants (20/group) was considered enough to determine feasibility issues and obtain treatment estimates for designing a full trial.

    Recruitment and study enrolment

    Participants will be primarily recruited through broadcasting in the public media (eg, newspapers and social media). Participants attending healthcare providers will also be invited to participate. The total recruitment period will be 1 year (June 2021 to May 2022). Advertisements will be placed in the local newspapers twice a month and social media once a month (Sponsored Facebook ad, for 1 week). Advertisement fliers will be placed around a tertiary hospital, regional healthcare practices and supermarkets. A recruitment email will be sent to the local tertiary educational university/polytechnic staff and students once every 2 months.

    All volunteers will complete an online screening form. Potential participants will be contacted by a researcher with a health professional background (trained musculoskeletal physiotherapist) to undergo further screening over the phone to confirm eligibility prior to study enrolment. The study information sheet (online supplemental file) will be emailed to eligible participants. Written informed consent will be obtained before baseline testing. At the baseline session, all participants will complete questionnaires to capture demographics, clinical characteristics of CLBP, including presence of central sensitivity (Central Sensitisation Inventory),71 72 neuropathic pain quality (PainDETECT),73 pain personification,74 and treatment expectancy and credibility.75

    Intervention procedures

    The intervention will be administered five times a week (30 min/session) for 4 weeks by an assistant research fellow trained by the primary investigator experienced in neuromodulation techniques. A battery-driven wireless TES (Starstim-Home TES, Neuroelectrics, Spain) will be used to deliver stimulation while participants are comfortably and quietly seated (figure 2). The HD technique uses arrays of multiple small electrodes whose configuration can be optimised for focally targeting specific brain regions.58 59 76–80 Eight small electrodes (~4 cm2) will be placed on a neoprene head cap following the International 10–20 electroencephalogram (EEG) system to simultaneously target pgACC, dACC and SSC (figures 2 and 3) (table 2).81 82

    View this table:
    Table 2

    Description of the HD-tIPNS intervention, as per the template for intervention description and replication

    Figure 2
    Figure 2

    The transcranial electrical stimulation set-up.

    Figure 3
    Figure 3

    Electrode positions and targeted brain regions. This figure presents results of the optimisation thatwas created using the Stimweaver software by the Neuroelectrics company for targeting the activity of pgACC, dACC and SSC.81 82 From left to right: Normal component of the E-field En (V/m), target E-field (V /m), target weight and ERNI (mV 2/m2) for grey matter. The optimal montage consists of eight channels that will be placed on the scalp following the international 10-20 EEG system. dACC, dorsal anterior cingulate cortex; EEG, electroencephalography; ERNI, Error Relative to No Intervention; pgACC, pregenual anterior cingulate cortex; SSC, primary somatosensory cortex.

    For HD-tIPNS group, the stimulation will be delivered at a current strength of a maximum of 2mA for 30 min, with 60 s ramp up and ramp down at the beginning and end of each stimulation session, with continuous stimulation in between. The pink noise stimulation at a current strength of a maximum of 0.6mA will be superimposed on the infraslow (0.1 Hz sinusoidal) waveform of a current intensity of 1mA. The current strength at each electrode will never exceed the maximum safety limit of 2mA. The intervention dosage is chosen based on the previous TES studies in CLBP33–41 43 44 and follows safety guidelines.83–85

    For the sham stimulation group, to create an identical skin sensation to active stimulation, we will use the Actisham protocol created by the Neuroelectrics.86 The current will be applied for a 60 s ramp up and 60 s ramp down at the beginning and end of each stimulation session, without any current for the remainder of the session. The duration of the sham session will be like HD-tIPNS session to blind the procedure appropriately. Participants in both groups will be informed that they may or may not perceive any sensations during the stimulation treatment. The previous TES studies have used this sham procedure and are shown to effectively blind participants to the stimulation condition, as it can induce the same scalp sensations perceived during active stimulation, both in terms of intensity and localisation. Further, the Actisham protocol will prevent the currents from reaching the cortex, thus avoiding causing any brain excitability changes.86

    Treatment fidelity will be assessed by the principal investigator at each session, who will supervise that the treatment is delivered in a standardised manner as planned. The treatment delivered for each participant for each session will be saved on the NIC2 computer software.

    Usual care/concomitant treatments: Participants will be permitted to continue their medications/exercises/other concomitant treatments for the duration of the trial, with the type and dosage being recorded at the baseline session. Any changes to their concomitant treatments will be recorded at every treatment and assessment session. Participants will be advised not to change any of their concomitant treatments for the duration of the trial. Participants with the intention of taking new medications or changing their treatment in the next 3 months will be excluded.

    Outcome measures

    An assessor, blinded to the group allocation, will collect outcomes at baseline (TB), immediately postintervention (Tim) and at follow-up of 1 week (T1wk), 1-month (T1m) and 3-month (T3m) postintervention. The chosen secondary measures have good psychometric properties, are used in clinical trials involving people with CLBP and are by recommendations.62–66

    Primary outcomes

    Feasibility measures

    • Recruitment rate, the number of participants recruited per month. Participants will be recruited over 1 year, with no threshold placed on the recruitment rate for each month. The recruitment rate will be recorded every week since the release of the advertisements, as well as the number of advertisements and the time period required to achieve the desired sample size (n=40).

    • The proportion of participants eligible and recruited from the total number screened (with reasons for exclusion), expressed as a percentage.

    • Adherence to intervention measured as number of treatment sessions attended by each participant expressed as a percentage of total number of sessions. Adherence rates will be calculated once the treatment phase is completed.

    • Drop-out rates, measured as the number of participants who dropped out in each group, expressed as a percentage of the total number of participants enrolled in the study. Drop-outs rates will be calculated once the follow-up phase is completed.

    Safety measures

    At each treatment and follow-up session, the treating researcher will record any adverse effects that likely have a causal relationship with the intervention. The following variables will be recorded:

    • Qualitative description and intensity of each symptom on a Likert scale (0=none to 10=extreme).

    • Relation of symptom to treatment, measured on a scale ranging from 1=unrelated to 5=strongly related.

    • Duration and time taken for resolution of each symptom expressed in minutes.

    • Worsening or improvement of symptoms: The Discontinuation-Emergent Sign and Symptom87 will be used to record worsening or improving side effects compared with status prior to previous session.

    • Any drop-outs due to adverse effects and how the adverse effects were managed.

    Acceptability and satisfaction

    Participant acceptability and satisfaction of the intervention will also be recorded quantitatively on an 11-point NRS (0=not at all acceptable/satisfied to 10=very acceptable/satisfied, respectively).

    Clinical measures

    Pain intensity and interference

    Using Brief Pain Inventory (BPI),88 a standardised, validated questionnaire for CLBP.

    Physical function

    Roland-Morris Disability Questionnaire67 68 will be used to assess self-reported functional abilities.

    Secondary outcomes

    Measures of peripheral and central sensitisation

    Quantitative sensory testing will be conducted and reported in accordance with the guidelines89 90 and our previous study (table 3).91

    View this table:
    Table 3

    List of the measure’s domains, their construct, measurement tools and assessment time points

    • Mechanical temporal summation (MTS): will be assessed using a nylon monofilament (Semmes monofilament 6.65, 300 g). Brief 10 repetitive contacts will be delivered at a rate of 1 Hz, externally cued by auditory stimuli. The participants will be asked to rate the level of pain experienced on NRS (0=no pain to 100=extreme pain) immediately after the first contact and to rate their greatest pain intensity after the 10th contact. Three trials will be conducted for each of the two regions (ie, symptomatic low back and non-dominant wrist) in random order. The location of these areas will be recorded using bony landmarks to ensure that same areas are re-assessed during follow-up. MTS will be calculated as difference between NRS rating after the first contact and the highest pain rating after the 10th contact for each trial. This score presents the maximum amount of MTS across 10 contact points. Average of three trials will be calculated, with a positive score indicating an increase in MTS. The MTS index will be defined as the ratio of ‘follow-up’ pain rating divided by ‘baseline’ pain rating.91–93

    • Pressure pain threshold (PPT): A computerised, handheld digital algometer (AlgoMed; Medoc, Ramat Yishai, Israel) will be used to measure three trials of PPT over two regions (symptomatic low back and non-dominant wrist) in random order. Two familiarisation trials will be performed at dominant mid-forearm before formal trials. The 1 cm2 algometer probe will be pressed over marked test site perpendicularly to the skin at a rate of 30 kPa/s. Participants will be instructed to press algometer trigger button in the patient control unit when pressure sensation changes to first pain.94 Once patient-controlled unit is activated, the trial is automatically terminated, and amount of pressure will be recorded. If participants did not report pain at maximum pressure level which is set at 1000 kPa for safety reasons, the procedure would be terminated, and a score of 1000 kpa will be assigned for that trial. The average of three trials will be calculated and used for analysis.95

    • Condition pain modulation (CPM) is the most frequently administered procedure for exploring the endogenous pain modulatory system.94 96 CPM test procedure will be administered at least 15–20 min after the MTS and PPT procedures with the previously published recommendations of testing.94 96

      • The conditioning stimulus will consist of a cold pressor task. The participants will immerse their dominant hand (until mid-forearm) in a thermos containing circulating cold water for a maximum period of 2 min. The cold water temperature will be maintained at ~5° centigrade and will be recorded immediately before and after the immersion procedure. Participants will be asked to continue hand immersion until the end of 2 min or until it is too uncomfortable to be kept immersed (NPRS ~80%). Participant’s pain during conditioning stimulus will be recorded on NPRS (0=no pain to 100=extreme pain) at every 15 s interval. A similar conditioning stimulus protocol has been used in previous studies showing a significant CPM effect.97

      • Test stimulus: A computerised, handheld digital algometer (AlgoMed; Medoc, Ramat Yishai, Israel) will be used to measure suprathreshold PPT (pain40) at the non-dominant leg region (tibialis anterior muscle). Two familiarisation trials will be performed at mid-forearm before the formal trials. The 1 cm2 algometer probe will be pressed over the marked test site perpendicularly to the skin at a rate of 30 kPa/s. The participants will be instructed to press the algometer trigger button in the patient control unit when the pressure sensation changes to a pain intensity of 40 out of 100 on the NRS. Once the patient-controlled unit is activated, the trial is automatically terminated, and the amount of pressure (kPa) will be recorded. Suppose participants did not report pain at the maximum pressure level which is set at 1000 kPa for safety reasons, the assessor will terminate the procedure, and a score of 1000 kpa will be assigned for that trial. Two PPT (pain40) trials will be recorded before conditioning stimulus and will be averaged to obtain a baseline score. In addition, three PPT (pain40) trials will be recorded in the same region at 30, 60 and 90 s immediately after the conditioning stimulus.

      • Calculation of CPM: A per cent change score will be calculated for each time point (ie, CPM30 s, CPM 60 s and CPM 90 s), with a positive score indicating an increase in PPTs (pain40) after the conditioning stimulus and thus the presence of CPM effect.

    Embedded Image

    Psychological measures

    Will include Depression, Anxiety and Stress Scale,98 to measure those three psychological constructs, Pain Catastrophising Scale,99 to measure extent of catastrophic thoughts and feelings about their pain,100 and Pain Vigilance and Awareness Questionnaire101 to measure frequency of habitual ‘attention to pain’.

    Secondary pain measures

    Pain unpleasantness (affective component) measured using an 11-point unpleasantness NRS (0=not at all unpleasant to 10=most unpleasant imaginable).102 103 Pain bothersomeness: measured using an 11-point bothersomeness NRS (0=not at all bothering to 10=most bothering).102 103 A categorical question will also be used ‘In the last 1 week, how bothersome has your low back pain been?’’ with five choices: ‘not at all’, ‘slightly’, ‘moderately’, ‘very much’ and ‘extremely’.104 105 The global rate of change106: assessed using the question ‘Compared with the beginning of treatment, how would you describe your back at this moment?’ Participants will rate their perceived change on an 11-point scale (−5=much worse, through 0=unchanged, to +5=completely, recovered).

    Quality of life and well-being

    Will be assessed using European Quality of Life-5 Dimensions scale107 and WHO-Five Well-Being Index,108 respectively.

    Measures of cortical electrical activity

    Resting-state EEG (~10 min, eyes-closed) will be obtained in a quiet room while the participant is sitting upright in a comfortable chair by an independent researcher blinded to the treatment group. Participants will be asked to refrain from caffeinated drinks. EEG data will be collected using the SynAmps RT Amplifier (Compudemics Neuroscan). The EEG will be sampled with 64 electrodes placed in the standard 10–10 International placement, and impedances will be checked to remain below 5 kΩ. The EEG data will then be resampled to 128 Hz, band-pass filtered (fast Fourier transform filter) to 0.01–44 Hz and re-referenced to the average reference using the EEGLAB function in Matlab. The data will then be plotted in EEGLAB for a careful inspection of artefacts and manual rejection.

    Standardised low-resolution brain electromagnetic tomography (sLORETA) will be used to estimate intracerebral electrical sources that generate scalp-recorded activity in each of the following 10 frequency bands, that is, infraslow (0.01–0.1 Hz), slow (0.2–1.5 Hz), delta (2–3.5 Hz), theta (4–7.5 Hz), alpha1 (8–10 Hz), alpha2 (10.5–12 Hz), beta1 (12.5–18 Hz), beta2 (18.5–21 Hz), beta3 (21.5–30 Hz) and gamma (30.5–44 Hz). The following three analyses will be used to explore the specific (ie, at the targeted cortical regions) and non-specific (ie, other cortical regions) effects of the HD-tIPNS on cortical activity and connectivity:

    • Whole-brain analysis: will be used to explore the overall (specific and non-specific) changes in the current density in the cortical regions. Comparisons will be made between prereatment and post-treatment measurements on a whole-brain by sLORETA statistical contrast maps through multiple voxel-by-voxel comparisons in a logarithm of t-ratio.109–111

    • Region of interest analysis: will be used to calculate and compare the log transformed current density changes at the targeted brain regions (pgACC, dACC and SSC). The ROI maker 1 function in sLORETA will be used to define the region of interest. A seed point will be provided for each region of interest and all voxels within a radius of 10 mm will be averaged to calculate the current density.

    • Lagged phase connectivity: will be used as a measure of coherence and will be calculated between all the regions of interest for all the 10 frequency bands as described above.109–111 Comparisons will be made between pretreatment and post-treatment measurements using sLORETA statistical contrast maps through multiple voxel-by-voxel comparisons in a logarithm of t-ratio.109–111

    Statistical analysis

    SPSS V.27.0 will be used for all statistical analyses. Descriptive statistics will be used to analyse feasibility, safety and acceptability measures. As this is a feasibility study, tests for significance to compare clinical or secondary measures between study groups will not performed, but descriptive statistics will be calculated.

    All measures will be analysed based on intention-to-treat principle and as per the originally assigned groups. Last observation carried forward methodology will be used to compute missing data. Mean±SDs and mean differences (95% CI) will be calculated from baseline to each interim and primary endpoint (T3m).

    Percentage change to baseline will be calculated for primary pain (BPI) and functional (RMDQ) measures as below (eg, for T3m):

    Embedded Image

    A≥30% decrease will be considered as a meaningful clinical important difference (MCID). Proportion of participants with changes ≥MCID will be calculated and descriptively compared between groups.

    A nested qualitative study

    We will include a nested qualitative study to explore participant’s experiences and acceptability of intervention procedures. Semistructured in-depth interviews will be conducted by a researcher, blinded to treatment allocation, immediately postintervention. All participants will be invited to participate. The aims of this study are explorative in nature and will evaluate participant’s experiences, exploring difficulties and barriers faced, perception towards intervention/research process, acceptability of intervention, perceived value and positive aspects of the study, and any other issues that arise during interviews. Table 4 presents the questions that will be used as a guide for the interview. The interviews will be audiorecorded and fully transcribed. The analysis will be guided by General Inductive Approach,112 113 which provides a pragmatic framework for identifying shared and individual experiences and embraces findings derived from both research objectives (deductive) and those arising directly from analysis of raw data (inductive). A constant comparison process will be used; researchers will reflect on and discuss completed interviews and revise the questions schedule accordingly to ensure a broad capture of new important information. The results of qualitative study will be published separately.

    View this table:
    Table 4

    Interview guide

    Patient and public involvement

    Patients or the public were not involved in the design, or conduct, or reporting, or dissemination plans of our research.

    Discussion

    To date, there are only a limited number of studies evaluating the TES interventions in people with CLBP.45 46 A recent meta-analysis demonstrates that there is moderate quality evidence suggesting that neither repeated sessions of non-invasive brain stimulation nor its combination with other treatments significantly improves pain or disability in people with CLBP.45 As most studies evaluating tDCS of single brain region demonstrated little success in improving pain and disability in people with CLBP, future trials focusing on different TES techniques, targeting multiple cortical areas, using various parameters are warranted and recommended. The proposed research will be the first randomised placebo-controlled pilot study to explore a novel HD-tIPNS technique targeting multiple brain regions simultaneously in individuals with CLBP.

    This pilot research will provide preliminary evidence on feasibility, safety, and acceptability of the novel HD-tIPNS technique for treatment of CLBP. Assessment of feasibility and acceptability of new interventions and study procedures is essential to determine parameters required to inform the study design of a future fully powered randomised controlled trial.114 Further, to the best of our knowledge, none of the previous studies have assessed the acceptability of the TES in people with CLBP. Our study will incorporate detailed mixed method approach to assess the feasibility and the acceptability of the HD-tIPNS techqniue and help inform interventions, study procedures and refinements and the planning of a future definitive randomised controlled trial. Additionally although our study is not powered to test effectiveness, it will provide treatment estimates to design the sample characteristics and numbers for a fully powered randomised controlled trial in future.

    Ethics, data safety and dissemination

    Ethical approval has been obtained from Health and Disability Ethics Committee (Ref:20/NTB/67), who may also audit the study investigators during or after the study. Any deviations from protocol will require Ethical amendment and will be updated in the registry. To protect participant confidentiality, any personal information collected will be destroyed at the end of the project. Each participant will be given a unique identification code, and the data will be linked to that code only. All study data will be securely stored in a locked filing cabinet or electronically with password protection, such that only those involved in the research programme will have access to it. As required by the University’s research policy, any unidentified raw data on which the results of the project depend will be kept in secure storage for 10 years, after which it will be destroyed.

    An independent data and safety monitoring committee will monitor the safety of the study. A serious adverse event (SAE) is defined as any untoward medical occurrence or effect that results in death, is life-threatening, requires hospitalisation, results in persistent or significant disability or incapacity. The study will be discontinued if there is any unexpected SAE, other unexpected events or if funding is completed/insufficient.

    Study findings will be reported to the regulatory and funding bodies, presented at the local, national, and international conferences, and disseminated by peer-review publication in a scientific journal.

    Ethics statements

    Patient consent for publication

    References

    1. ↵
      1. Clark S,
      2. Horton R
      . Low back pain: a major global challenge. Lancet 2018;391:2302.doi:10.1016/S0140-6736(18)30725-6pmid:http://www.ncbi.nlm.nih.gov/pubmed/29573869
      OpenUrlPubMed
    2. ↵
      1. Hoy D,
      2. March L,
      3. Brooks P, et al
      . The global burden of low back pain: estimates from the global burden of disease 2010 study. Ann Rheum Dis 2014;73:968–74.doi:10.1136/annrheumdis-2013-204428pmid:http://www.ncbi.nlm.nih.gov/pubmed/24665116
      OpenUrlAbstract/FREE Full Text
    3. ↵
      1. Treede R-D,
      2. Rief W,
      3. Barke A, et al
      . A classification of chronic pain for ICD-11. Pain 2015;156:1003.doi:10.1097/j.pain.0000000000000160pmid:http://www.ncbi.nlm.nih.gov/pubmed/25844555
      OpenUrlCrossRefPubMed
    4. ↵
      1. Chou R,
      2. Deyo R,
      3. Friedly J, et al
      . Nonpharmacologic therapies for low back pain: a systematic review for an American College of physicians clinical practice guideline. Ann Intern Med 2017;166:493–505.doi:10.7326/M16-2459pmid:http://www.ncbi.nlm.nih.gov/pubmed/28192793
      OpenUrlCrossRefPubMed
    5. ↵
      1. Coulter ID,
      2. Crawford C,
      3. Hurwitz EL, et al
      . Manipulation and mobilization for treating chronic low back pain: a systematic review and meta-analysis. Spine J 2018;18:866–79.doi:10.1016/j.spinee.2018.01.013pmid:http://www.ncbi.nlm.nih.gov/pubmed/29371112
      OpenUrlCrossRefPubMed
    6. ↵
      1. Rubinstein SM,
      2. de Zoete A,
      3. van Middelkoop M, et al
      . Benefits and harms of spinal manipulative therapy for the treatment of chronic low back pain: systematic review and meta-analysis of randomised controlled trials. BMJ 2019;364:l689.doi:10.1136/bmj.l689pmid:http://www.ncbi.nlm.nih.gov/pubmed/30867144
      OpenUrlAbstract/FREE Full Text
    7. ↵
      1. Chou R,
      2. Turner JA,
      3. Devine EB, et al
      . The effectiveness and risks of long-term opioid therapy for chronic pain: a systematic review for a national Institutes of health pathways to prevention workshop. Ann Intern Med 2015;162:276–86.doi:10.7326/M14-2559pmid:http://www.ncbi.nlm.nih.gov/pubmed/25581257
      OpenUrlCrossRefPubMed
    8. ↵
      1. Koes BW,
      2. Backes D,
      3. Bindels PJE
      . Pharmacotherapy for chronic non-specific low back pain: current and future options. Expert Opin Pharmacother 2018;19:537–45.doi:10.1080/14656566.2018.1454430pmid:http://www.ncbi.nlm.nih.gov/pubmed/29578822
      OpenUrlPubMed
    9. ↵
      1. Pavelka K,
      2. Jarosova H,
      3. Sleglova O, et al
      . Chronic low back pain: current pharmacotherapeutic therapies and a new biological approach. Curr Med Chem 2019;26:1019–26.doi:10.2174/0929867325666180514102146pmid:http://www.ncbi.nlm.nih.gov/pubmed/29756567
      OpenUrlPubMed
    10. ↵
      1. Ng SK,
      2. Urquhart DM,
      3. Fitzgerald PB, et al
      . The relationship between structural and functional brain changes and altered emotion and cognition in chronic low back pain brain changes: a systematic review of MRI and fMRI studies. Clin J Pain 2018;34:237–61.doi:10.1097/AJP.0000000000000534pmid:http://www.ncbi.nlm.nih.gov/pubmed/28719509
      OpenUrlPubMed
    11. ↵
      1. Konno S-I,
      2. Sekiguchi M
      . Association between brain and low back pain. J Orthop Sci 2018;23:3–7.doi:10.1016/j.jos.2017.11.007pmid:http://www.ncbi.nlm.nih.gov/pubmed/29167069
      OpenUrlPubMed
    12. ↵
      Structural and functional brain abnormalities in chronic low back pain: a systematic review☆. seminars in arthritis and rheumatism. Elsevier 2015.
    13. ↵
      1. Kucyi A,
      2. Davis KD
      . The dynamic pain connectome. Trends Neurosci 2015;38:86–95.doi:10.1016/j.tins.2014.11.006pmid:http://www.ncbi.nlm.nih.gov/pubmed/25541287
      OpenUrlCrossRefPubMed
    14. ↵
      1. Vanneste S,
      2. De Ridder D
      . Chronic pain as a brain imbalance between pain input and pain suppression. Brain Commun 2021;3:fcab014.doi:10.1093/braincomms/fcab014pmid:http://www.ncbi.nlm.nih.gov/pubmed/33758824
      OpenUrlPubMed
    15. ↵
      1. De Ridder D,
      2. Vanneste S
      . The Bayesian brain in imbalance: medial, lateral and descending pathways in tinnitus and pain: a perspective. Progress in Brain Research: Elsevier, 2021: 309–34.
    16. ↵
      1. De Ridder D,
      2. Adhia D,
      3. Vanneste S
      . The anatomy of pain and suffering in the brain and its clinical implications. Neurosci Biobehav Rev 2021;130:125-146.doi:10.1016/j.neubiorev.2021.08.013pmid:http://www.ncbi.nlm.nih.gov/pubmed/34411559
      OpenUrlPubMed
    17. ↵
      1. Li T,
      2. Zhang S,
      3. Kurata J
      . Suppressed descending pain modulatory and enhanced sensorimotor networks in patients with chronic low back pain. J Anesth 2018;32:831–43.doi:10.1007/s00540-018-2561-1pmid:http://www.ncbi.nlm.nih.gov/pubmed/30264383
      OpenUrlPubMed
    18. ↵
      1. Yuan C,
      2. Shi H,
      3. Pan P, et al
      . Gray matter abnormalities associated with chronic back pain. Clin J Pain 2017;33:983–90.doi:10.1097/AJP.0000000000000489
      OpenUrl
    19. ↵
      1. De Ridder D,
      2. Vanneste S
      . Burst and tonic spinal cord stimulation: different and common brain mechanisms. Neuromodulation 2016;19:47–59.doi:10.1111/ner.12368pmid:http://www.ncbi.nlm.nih.gov/pubmed/26586145
      OpenUrlPubMed
    20. ↵
      1. Bushnell MC,
      2. Čeko M,
      3. Low LA
      . Cognitive and emotional control of pain and its disruption in chronic pain. Nat Rev Neurosci 2013;14:502–11.doi:10.1038/nrn3516pmid:http://www.ncbi.nlm.nih.gov/pubmed/23719569
      OpenUrlCrossRefPubMed
    21. ↵
      1. Baliki MN,
      2. Petre B,
      3. Torbey S, et al
      . Corticostriatal functional connectivity predicts transition to chronic back pain. Nat Neurosci 2012;15:1117–9.doi:10.1038/nn.3153pmid:http://www.ncbi.nlm.nih.gov/pubmed/22751038
      OpenUrlCrossRefPubMed
    22. ↵
      1. Coppieters I,
      2. Meeus M,
      3. Kregel J, et al
      . Relations between brain alterations and clinical pain measures in chronic musculoskeletal pain: a systematic review. J Pain 2016;17:949–62.doi:10.1016/j.jpain.2016.04.005pmid:http://www.ncbi.nlm.nih.gov/pubmed/27263992
      OpenUrlPubMed
    23. ↵
      1. Hashmi JA,
      2. Baliki MN,
      3. Huang L, et al
      . Shape shifting pain: chronification of back pain shifts brain representation from nociceptive to emotional circuits. Brain 2013;136:2751–68.doi:10.1093/brain/awt211pmid:http://www.ncbi.nlm.nih.gov/pubmed/23983029
      OpenUrlCrossRefPubMedWeb of Science
    24. ↵
      1. Hemington KS,
      2. Rogachov A,
      3. Cheng JC, et al
      . Patients with chronic pain exhibit a complex relationship triad between pain, resilience, and within- and cross-network functional connectivity of the default mode network. Pain 2018;159:1621–30.doi:10.1097/j.pain.0000000000001252pmid:http://www.ncbi.nlm.nih.gov/pubmed/29697536
      OpenUrlPubMed
    25. ↵
      1. Kim J,
      2. Mawla I,
      3. Kong J, et al
      . Somatotopically specific primary somatosensory connectivity to salience and default mode networks encodes clinical pain. Pain 2019;160:1594.doi:10.1097/j.pain.0000000000001541pmid:http://www.ncbi.nlm.nih.gov/pubmed/30839429
      OpenUrlCrossRefPubMed
    26. ↵
      1. Kong J,
      2. Spaeth RB,
      3. Wey H-Y, et al
      . S1 is associated with chronic low back pain: a functional and structural MRI study. Mol Pain 2013;9:1744.doi:10.1186/1744-8069-9-43pmid:http://www.ncbi.nlm.nih.gov/pubmed/23965184
      OpenUrlPubMed
    27. ↵
      1. Ossipov MH,
      2. Morimura K,
      3. Porreca F
      . Descending pain modulation and chronification of pain. Curr Opin Support Palliat Care 2014;8:143.doi:10.1097/SPC.0000000000000055pmid:http://www.ncbi.nlm.nih.gov/pubmed/24752199
      OpenUrlCrossRefPubMed
    28. ↵
      1. Tu Y,
      2. Jung M,
      3. Gollub RL, et al
      . Abnormal medial prefrontal cortex functional connectivity and its association with clinical symptoms in chronic low back pain. Pain 2019;160:1308.doi:10.1097/j.pain.0000000000001507pmid:http://www.ncbi.nlm.nih.gov/pubmed/31107712
      OpenUrlCrossRefPubMed
    29. ↵
      1. Nascimento RMD,
      2. Cavalcanti RL,
      3. Souza CG, et al
      . Transcranial direct current stimulation combined with peripheral stimulation in chronic pain: a systematic review and meta-analysis. Expert Rev Med Devices 2022:1–20 (published Online First: 2022/02/09).doi:10.1080/17434440.2022.2039623pmid:http://www.ncbi.nlm.nih.gov/pubmed/35130800
    30. ↵
      1. Pinto CB,
      2. Teixeira Costa B,
      3. Duarte D, et al
      . Transcranial direct current stimulation as a therapeutic tool for chronic pain. J Ect 2018;34:e36–50.doi:10.1097/YCT.0000000000000518pmid:http://www.ncbi.nlm.nih.gov/pubmed/29952860
      OpenUrlPubMed
    31. ↵
      1. Knotkova H,
      2. Hamani C,
      3. Sivanesan E, et al
      . Neuromodulation for chronic pain. Lancet 2021;397:2111–24.doi:10.1016/S0140-6736(21)00794-7pmid:http://www.ncbi.nlm.nih.gov/pubmed/34062145
      OpenUrlPubMed
    32. ↵
      1. Lloyd DM,
      2. Wittkopf PG,
      3. Arendsen LJ, et al
      . Is transcranial direct current stimulation (tDCS) effective for the treatment of pain in fibromyalgia? A systematic review and meta-analysis. J Pain 2020;21:1085–100.doi:10.1016/j.jpain.2020.01.003pmid:http://www.ncbi.nlm.nih.gov/pubmed/31982685
      OpenUrlPubMed
    33. ↵
      1. Ahn S,
      2. Prim JH,
      3. Alexander ML, et al
      . Identifying and engaging neuronal oscillations by transcranial alternating current stimulation in patients with chronic low back pain: a randomized, crossover, double-blind, sham-controlled pilot study. J Pain 2019;20:277.e1-277.e11.doi:10.1016/j.jpain.2018.09.004pmid:http://www.ncbi.nlm.nih.gov/pubmed/30268803
      OpenUrlPubMed
    34. ↵
      1. Hazime FA,
      2. Baptista AF,
      3. de Freitas DG, et al
      . Treating low back pain with combined cerebral and peripheral electrical stimulation: a randomized, double-blind, factorial clinical trial. Eur J Pain 2017;21:1132–43.doi:10.1002/ejp.1037pmid:http://www.ncbi.nlm.nih.gov/pubmed/28440001
      OpenUrlPubMed
    35. ↵
      1. Jafarzadeh A,
      2. Ehsani F,
      3. Yosephi MH, et al
      . Concurrent postural training and M1 anodal transcranial direct current stimulation improve postural impairment in patients with chronic low back pain. J Clin Neurosci 2019;68:224–34.doi:10.1016/j.jocn.2019.07.017pmid:http://www.ncbi.nlm.nih.gov/pubmed/31350080
      OpenUrlPubMed
    36. ↵
      1. Luedtke K,
      2. Rushton A,
      3. Wright C, et al
      . Effectiveness of transcranial direct current stimulation preceding cognitive behavioural management for chronic low back pain: sham controlled double blinded randomised controlled trial. BMJ 2015;350:h1640.doi:10.1136/bmj.h1640pmid:http://www.ncbi.nlm.nih.gov/pubmed/25883244
      OpenUrlAbstract/FREE Full Text
    37. ↵
      1. Mariano TY,
      2. Burgess FW,
      3. Bowker M, et al
      . Transcranial direct current stimulation for affective symptoms and functioning in chronic low back pain: a pilot double-blinded, randomized, placebo-controlled trial. Pain Med 2019;20:1166–77.doi:10.1093/pm/pny188pmid:http://www.ncbi.nlm.nih.gov/pubmed/30358864
      OpenUrlPubMed
    38. ↵
      1. O'Connell NE,
      2. Cossar J,
      3. Marston L, et al
      . Transcranial direct current stimulation of the motor cortex in the treatment of chronic nonspecific low back pain: a randomized, double-blind exploratory study. Clin J Pain 2013;29:26–34.doi:10.1097/AJP.0b013e318247ec09pmid:http://www.ncbi.nlm.nih.gov/pubmed/23221623
      OpenUrlCrossRefPubMed
    39. ↵
      1. Schabrun SM,
      2. Burns E,
      3. Thapa T, et al
      . The response of the primary motor cortex to neuromodulation is altered in chronic low back pain: a preliminary study. Pain Med 2018;19:1227–36.doi:10.1093/pm/pnx168pmid:http://www.ncbi.nlm.nih.gov/pubmed/29016867
      OpenUrlPubMed
    40. ↵
      1. Schabrun SM,
      2. Jones E,
      3. Elgueta Cancino EL, et al
      . Targeting chronic recurrent low back pain from the top-down and the bottom-up: a combined transcranial direct current stimulation and peripheral electrical stimulation intervention. Brain Stimul 2014;7:451–9.doi:10.1016/j.brs.2014.01.058pmid:http://www.ncbi.nlm.nih.gov/pubmed/24582372
      OpenUrlPubMed
    41. ↵
      1. Straudi S,
      2. Buja S,
      3. Baroni A, et al
      . The effects of transcranial direct current stimulation (tDCS) combined with group exercise treatment in subjects with chronic low back pain: a pilot randomized control trial. Clin Rehabil 2018;32:1348–56.doi:10.1177/0269215518777881pmid:http://www.ncbi.nlm.nih.gov/pubmed/29783893
      OpenUrlPubMed
    42. ↵
      1. Jiang N,
      2. Wei J,
      3. Li G, et al
      . Effect of dry-electrode-based transcranial direct current stimulation on chronic low back pain and low back muscle activities: a double-blind sham-controlled study. Restor Neurol Neurosci 2020;38:41–54.doi:10.3233/RNN-190922pmid:http://www.ncbi.nlm.nih.gov/pubmed/31683491
      OpenUrlPubMed
    43. ↵
      1. Larie MS,
      2. Esfandiarpour F,
      3. Riahi F, et al
      . Effects of cortical and peripheral electrical stimulation on brain activity in individuals with chronic low back pain. PTJ 2019;9:39–46.doi:10.32598/PTJ.9.1.39
      OpenUrl
    44. ↵
      1. Ouellette AL,
      2. Liston MB,
      3. Chang W-J, et al
      . Safety and feasibility of transcranial direct current stimulation (tDCS) combined with sensorimotor retraining in chronic low back pain: a protocol for a pilot randomised controlled trial. BMJ Open 2017;7:e013080.doi:10.1136/bmjopen-2016-013080pmid:http://www.ncbi.nlm.nih.gov/pubmed/28827229
      OpenUrlAbstract/FREE Full Text
    45. ↵
      1. Patricio P,
      2. Roy J-S,
      3. Rohel A, et al
      . The effect of noninvasive brain stimulation to reduce nonspecific low back pain: a systematic review and meta-analysis. Clin J Pain 2021;37:475–85.doi:10.1097/AJP.0000000000000934pmid:http://www.ncbi.nlm.nih.gov/pubmed/33949359
      OpenUrlPubMed
    46. ↵
      1. O'Connell NE,
      2. Marston L,
      3. Spencer S, et al
      . Non-Invasive brain stimulation techniques for chronic pain. Cochrane Database Syst Rev 2018;3:Cd008208.doi:10.1002/14651858.CD008208.pub4pmid:http://www.ncbi.nlm.nih.gov/pubmed/29547226
      OpenUrlPubMed
    47. ↵
      1. Lima MC,
      2. Fregni F
      . Motor cortex stimulation for chronic pain: systematic review and meta-analysis of the literature. Neurology 2008;70:2329–37.doi:10.1212/01.wnl.0000314649.38527.93pmid:http://www.ncbi.nlm.nih.gov/pubmed/18541887
      OpenUrlCrossRefPubMed
    48. ↵
      1. Brookes MJ,
      2. Woolrich M,
      3. Luckhoo H, et al
      . Investigating the electrophysiological basis of resting state networks using magnetoencephalography. Proc Natl Acad Sci U S A 2011;108:16783–8.doi:10.1073/pnas.1112685108pmid:http://www.ncbi.nlm.nih.gov/pubmed/21930901
      OpenUrlAbstract/FREE Full Text
    49. ↵
      1. Mitra A,
      2. Raichle ME
      . How networks communicate: propagation patterns in spontaneous brain activity. Philos Trans R Soc Lond B Biol Sci 2016;371:20150546.doi:10.1098/rstb.2015.0546pmid:http://www.ncbi.nlm.nih.gov/pubmed/27574315
      OpenUrlCrossRefPubMed
    50. ↵
      1. Watson BO
      . Cognitive and physiologic impacts of the infraslow oscillation. Front Syst Neurosci 2018;12:44.doi:10.3389/fnsys.2018.00044pmid:http://www.ncbi.nlm.nih.gov/pubmed/30386218
      OpenUrlCrossRefPubMed
    51. ↵
      1. Wilckens KA,
      2. Ferrarelli F,
      3. Walker MP, et al
      . Slow-Wave activity enhancement to improve cognition. Trends Neurosci 2018;41:470–82.doi:10.1016/j.tins.2018.03.003pmid:http://www.ncbi.nlm.nih.gov/pubmed/29628198
      OpenUrlCrossRefPubMed
    52. ↵
      1. Chan AW,
      2. Mohajerani MH,
      3. LeDue JM, et al
      . Mesoscale infraslow spontaneous membrane potential fluctuations recapitulate high-frequency activity cortical motifs. Nat Commun 2015;6:1–12.doi:10.1038/ncomms8738pmid:http://www.ncbi.nlm.nih.gov/pubmed/26190168
      OpenUrlCrossRefPubMed
    53. ↵
      1. Pan W-J,
      2. Thompson GJ,
      3. Magnuson ME, et al
      . Infraslow LFP correlates to resting-state fMRI BOLD signals. Neuroimage 2013;74:288–97.doi:10.1016/j.neuroimage.2013.02.035pmid:http://www.ncbi.nlm.nih.gov/pubmed/23481462
      OpenUrlCrossRefPubMedWeb of Science
    54. ↵
      1. Ploner M,
      2. Sorg C,
      3. Gross J
      . Brain rhythms of pain. Trends Cogn Sci 2017;21:100–10.doi:10.1016/j.tics.2016.12.001pmid:http://www.ncbi.nlm.nih.gov/pubmed/28025007
      OpenUrlCrossRefPubMed
    55. ↵
      1. Alshelh Z,
      2. Di Pietro F,
      3. Youssef AM, et al
      . Chronic neuropathic pain: it's about the rhythm. J Neurosci 2016;36:1008–18.doi:10.1523/JNEUROSCI.2768-15.2016pmid:http://www.ncbi.nlm.nih.gov/pubmed/26791228
      OpenUrlAbstract/FREE Full Text
    56. ↵
      1. Zhang B,
      2. Jung M,
      3. Tu Y, et al
      . Identifying brain regions associated with the neuropathology of chronic low back pain: a resting-state amplitude of low-frequency fluctuation study. Br J Anaesth 2019;123:e303–11.doi:10.1016/j.bja.2019.02.021pmid:http://www.ncbi.nlm.nih.gov/pubmed/30948036
      OpenUrlPubMed
    57. ↵
      1. Zhou F,
      2. Gu L,
      3. Hong S, et al
      . Altered low-frequency oscillation amplitude of resting state-fMRI in patients with discogenic low-back and leg pain. J Pain Res 2018;11:165.doi:10.2147/JPR.S151562pmid:http://www.ncbi.nlm.nih.gov/pubmed/29386913
      OpenUrlPubMed
    58. ↵
      1. Leong SL,
      2. De Ridder D,
      3. Vanneste S, et al
      . High definition transcranial pink noise stimulation of anterior cingulate cortex on food craving: an explorative study. Appetite 2018;120:673–8.doi:10.1016/j.appet.2017.10.034pmid:http://www.ncbi.nlm.nih.gov/pubmed/29079475
      OpenUrlPubMed
    59. ↵
      1. Whittington F,
      2. De Ridder D,
      3. Adhia DB
      . High definition transcranial infraslow pink noise stimulation for improving executive functioning in healthy older adults – a pilot safety trial. N Z Med J 2021.
    60. ↵
      1. Chan A-W,
      2. Tetzlaff JM,
      3. Altman DG, et al
      . Spirit 2013 statement: defining standard protocol items for clinical trials. Ann Intern Med 2013;158:200–7.doi:10.7326/0003-4819-158-3-201302050-00583pmid:http://www.ncbi.nlm.nih.gov/pubmed/23295957
      OpenUrlCrossRefPubMedWeb of Science
    61. ↵
      1. Hoffmann TC,
      2. Glasziou PP,
      3. Boutron I, et al
      . Better reporting of interventions: template for intervention description and replication (TIDieR) checklist and guide. BMJ 2014;348:g1687.doi:10.1136/bmj.g1687pmid:http://www.ncbi.nlm.nih.gov/pubmed/24609605
      OpenUrlAbstract/FREE Full Text
    62. ↵
      1. Edwards RR,
      2. Dworkin RH,
      3. Turk DC, et al
      . Patient phenotyping in clinical trials of chronic pain treatments: IMMPACT recommendations. Pain 2016;157:1851-1871.doi:10.1097/j.pain.0000000000000602pmid:http://www.ncbi.nlm.nih.gov/pubmed/27152687
      OpenUrlPubMed
    63. ↵
      1. Gewandter JS,
      2. Dworkin RH,
      3. Turk DC, et al
      . Improving study conduct and data quality in clinical trials of chronic pain treatments: IMMPACT recommendations. J Pain 2020;21:931–42.doi:10.1016/j.jpain.2019.12.003pmid:http://www.ncbi.nlm.nih.gov/pubmed/31843583
      OpenUrlPubMed
    64. ↵
      1. Smith SM,
      2. Dworkin RH,
      3. Turk DC, et al
      . The potential role of sensory testing, skin biopsy, and functional brain imaging as biomarkers in chronic pain clinical trials: IMMPACT considerations. J Pain 2017;18:757–77.doi:10.1016/j.jpain.2017.02.429pmid:http://www.ncbi.nlm.nih.gov/pubmed/28254585
      OpenUrlCrossRefPubMed
    65. ↵
      1. Smith SM,
      2. Dworkin RH,
      3. Turk DC, et al
      . Interpretation of chronic pain clinical trial outcomes: IMMPACT recommended considerations. Pain 2020;161:2446–61.doi:10.1097/j.pain.0000000000001952pmid:http://www.ncbi.nlm.nih.gov/pubmed/32520773
      OpenUrlPubMed
    66. ↵
      1. Taylor AM,
      2. Phillips K,
      3. Patel KV, et al
      . Assessment of physical function and participation in chronic pain clinical trials: IMMPACT/OMERACT recommendations. Pain 2016;157:1836-1850.doi:10.1097/j.pain.0000000000000577pmid:http://www.ncbi.nlm.nih.gov/pubmed/27058676
      OpenUrlPubMed
    67. ↵
      1. Roland M,
      2. Morris R
      . A study of the natural history of low-back pain. Part II: development of guidelines for trials of treatment in primary care. Spine 1983;8:145–50.doi:10.1097/00007632-198303000-00005pmid:http://www.ncbi.nlm.nih.gov/pubmed/6222487
      OpenUrlCrossRefPubMedWeb of Science
    68. ↵
      1. Roland M,
      2. Morris R
      . A study of the natural history of back pain. Part I: development of a reliable and sensitive measure of disability in low-back pain. Spine 1983;8:141-4.doi:10.1097/00007632-198303000-00004pmid:http://www.ncbi.nlm.nih.gov/pubmed/6222486
      OpenUrlPubMed
    69. ↵
      1. Dionne CE,
      2. Dunn KM,
      3. Croft PR, et al
      . A consensus approach toward the standardization of back pain definitions for use in prevalence studies. Spine 2008;33:95–103.doi:10.1097/BRS.0b013e31815e7f94pmid:http://www.ncbi.nlm.nih.gov/pubmed/18165754
      OpenUrlCrossRefPubMedWeb of Science
    70. ↵
      1. Grotle M,
      2. Brox JI,
      3. Vøllestad NK
      . Concurrent comparison of responsiveness in pain and functional status measurements used for patients with low back pain. Spine 2004;29:E492–501.doi:10.1097/01.brs.0000143664.02702.0bpmid:http://www.ncbi.nlm.nih.gov/pubmed/15507789
      OpenUrlCrossRefPubMedWeb of Science
    71. ↵
      1. Neblett R,
      2. Cohen H,
      3. Choi Y, et al
      . The central sensitization inventory (CsI): establishing clinically significant values for identifying central sensitivity syndromes in an outpatient chronic pain sample. J Pain 2013;14:438–45.doi:10.1016/j.jpain.2012.11.012pmid:http://www.ncbi.nlm.nih.gov/pubmed/23490634
      OpenUrlCrossRefPubMedWeb of Science
    72. ↵
      1. Mayer TG,
      2. Neblett R,
      3. Cohen H, et al
      . The development and psychometric validation of the central sensitization inventory. Pain Pract 2012;12:276–85.doi:10.1111/j.1533-2500.2011.00493.xpmid:http://www.ncbi.nlm.nih.gov/pubmed/21951710
      OpenUrlCrossRefPubMedWeb of Science
    73. ↵
      1. Freynhagen R,
      2. Tölle TR,
      3. Gockel U, et al
      . The painDETECT project - far more than a screening tool on neuropathic pain. Curr Med Res Opin 2016;32:1033–57.doi:10.1185/03007995.2016.1157460pmid:http://www.ncbi.nlm.nih.gov/pubmed/26907456
      OpenUrlPubMed
    74. ↵
      1. Schattner E,
      2. Shahar G
      . Role of pain personification in pain-related depression: an object relations perspective. Psychiatry 2011;74:14–20.doi:10.1521/psyc.2011.74.1.14pmid:http://www.ncbi.nlm.nih.gov/pubmed/21463166
      OpenUrlPubMed
    75. ↵
      1. Devilly GJ,
      2. Borkovec TD
      . Psychometric properties of the credibility/expectancy questionnaire. J Behav Ther Exp Psychiatry 2000;31:73–86.doi:10.1016/s0005-7916(00)00012-4pmid:http://www.ncbi.nlm.nih.gov/pubmed/11132119
      OpenUrlCrossRefPubMedWeb of Science
    76. ↵
      1. Minhas P,
      2. Bansal V,
      3. Patel J, et al
      . Electrodes for high-definition transcutaneous DC stimulation for applications in drug delivery and electrotherapy, including tDCS. J Neurosci Methods 2010;190:188–97.doi:10.1016/j.jneumeth.2010.05.007pmid:http://www.ncbi.nlm.nih.gov/pubmed/20488204
      OpenUrlCrossRefPubMed
    77. ↵
      1. DaSilva AF,
      2. Truong DQ,
      3. DosSantos MF, et al
      . State-Of-Art neuroanatomical target analysis of high-definition and conventional tDCS montages used for migraine and pain control. Front Neuroanat 2015;9:89.doi:10.3389/fnana.2015.00089pmid:http://www.ncbi.nlm.nih.gov/pubmed/26236199
      OpenUrlCrossRefPubMed
    78. ↵
      1. Datta A,
      2. Bansal V,
      3. Diaz J, et al
      . Gyri-precise head model of transcranial direct current stimulation: improved spatial focality using a ring electrode versus conventional rectangular pad. Brain Stimul 2009;2:201-7, 207.e1.doi:10.1016/j.brs.2009.03.005pmid:http://www.ncbi.nlm.nih.gov/pubmed/20648973
      OpenUrlPubMed
    79. ↵
      1. Dmochowski JP,
      2. Datta A,
      3. Bikson M, et al
      . Optimized multi-electrode stimulation increases focality and intensity at target. J Neural Eng 2011;8:046011.doi:10.1088/1741-2560/8/4/046011pmid:http://www.ncbi.nlm.nih.gov/pubmed/21659696
      OpenUrlCrossRefPubMed
    80. ↵
      1. WT T,
      2. Eroh J,
      3. Hart J
      . Exploring the effects of anodal and cathodal high definition transcranial direct current stimulation targeting the dorsal anterior cingulate cortex. Sci Rep 2018;8:1–16.doi:10.1038/s41598-018-22730-x
      OpenUrlCrossRefPubMed
    81. ↵
      1. Ruffini G,
      2. Fox MD,
      3. Ripolles O, et al
      . Optimization of multifocal transcranial current stimulation for weighted cortical pattern targeting from realistic modeling of electric fields. Neuroimage 2014;89:216–25.doi:10.1016/j.neuroimage.2013.12.002pmid:http://www.ncbi.nlm.nih.gov/pubmed/24345389
      OpenUrlCrossRefPubMedWeb of Science
    82. ↵
      1. Ruffini G,
      2. Wendling F,
      3. Sanchez-Todo R, et al
      . Targeting brain networks with multichannel transcranial current stimulation (tCS). Curr Opin Biomed Eng 2018;8:70–7.doi:10.1016/j.cobme.2018.11.001
      OpenUrl
    83. ↵
      1. Lefaucheur J-P,
      2. Antal A,
      3. Ayache SS, et al
      . Evidence-Based guidelines on the therapeutic use of transcranial direct current stimulation (tDCS). Clin Neurophysiol 2017;128:56–92.doi:10.1016/j.clinph.2016.10.087pmid:http://www.ncbi.nlm.nih.gov/pubmed/27866120
      OpenUrlCrossRefPubMed
    84. ↵
      1. Nikolin S,
      2. Huggins C,
      3. Martin D, et al
      . Safety of repeated sessions of transcranial direct current stimulation: a systematic review. Brain Stimul 2018;11:278–88.doi:10.1016/j.brs.2017.10.020pmid:http://www.ncbi.nlm.nih.gov/pubmed/29169814
      OpenUrlPubMed
    85. ↵
      1. Woods AJ,
      2. Antal A,
      3. Bikson M, et al
      . A technical guide to tDCS, and related non-invasive brain stimulation tools. Clin Neurophysiol 2016;127:1031–48.doi:10.1016/j.clinph.2015.11.012pmid:http://www.ncbi.nlm.nih.gov/pubmed/26652115
      OpenUrlCrossRefPubMed
    86. ↵
      1. Neri F,
      2. Mencarelli L,
      3. Menardi A, et al
      . A novel tDCS sham approach based on model-driven controlled shunting. Brain Stimul 2020;13:507–16.doi:10.1016/j.brs.2019.11.004pmid:http://www.ncbi.nlm.nih.gov/pubmed/31926812
      OpenUrlPubMed
    87. ↵
      1. Rosenbaum JF,
      2. Fava M,
      3. Hoog SL, et al
      . Selective serotonin reuptake inhibitor discontinuation syndrome: a randomized clinical trial. Biol Psychiatry 1998;44:77–87.doi:10.1016/s0006-3223(98)00126-7pmid:http://www.ncbi.nlm.nih.gov/pubmed/9646889
      OpenUrlCrossRefPubMedWeb of Science
    88. ↵
      1. Song C-Y,
      2. Lin S-F,
      3. Huang C-Y, et al
      . Validation of the brief pain inventory in patients with low back pain. Spine 2016;41:E937–42.doi:10.1097/BRS.0000000000001478pmid:http://www.ncbi.nlm.nih.gov/pubmed/26839985
      OpenUrlPubMed
    89. ↵
      1. Uddin Z,
      2. MacDermid JC
      . Quantitative sensory testing in chronic musculoskeletal pain. Pain Med 2016;17:1694–703.doi:10.1093/pm/pnv105pmid:http://www.ncbi.nlm.nih.gov/pubmed/26893116
      OpenUrlPubMed
    90. ↵
      1. Rolke R,
      2. Baron R,
      3. Maier C,
      4. Ca M, et al
      . Quantitative sensory testing in the German research network on neuropathic pain (DFNS): standardized protocol and reference values. Pain 2006;123:231–43.doi:10.1016/j.pain.2006.01.041pmid:http://www.ncbi.nlm.nih.gov/pubmed/16697110
      OpenUrlCrossRefPubMedWeb of Science
    91. ↵
      1. Mani R,
      2. Adhia DB,
      3. Leong SL, et al
      . Sedentary behaviour facilitates conditioned pain modulation in middle-aged and older adults with persistent musculoskeletal pain: a cross-sectional investigation. Pain Rep 2019;4:e773–e73.doi:10.1097/PR9.0000000000000773pmid:http://www.ncbi.nlm.nih.gov/pubmed/31875181
      OpenUrlPubMed
    92. ↵
      1. Goodin BR,
      2. Bulls HW,
      3. Herbert MS, et al
      . Temporal summation of pain as a prospective predictor of clinical pain severity in adults aged 45 years and older with knee osteoarthritis: ethnic differences. Psychosom Med 2014;76:302–10.doi:10.1097/PSY.0000000000000058pmid:http://www.ncbi.nlm.nih.gov/pubmed/24804882
      OpenUrlCrossRefPubMed
    93. ↵
      1. Hübscher M,
      2. Moloney N,
      3. Leaver A, et al
      . Relationship between quantitative sensory testing and pain or disability in people with spinal pain-a systematic review and meta-analysis. Pain 2013;154:1497–504.doi:10.1016/j.pain.2013.05.031pmid:http://www.ncbi.nlm.nih.gov/pubmed/23711482
      OpenUrlCrossRefPubMedWeb of Science
    94. ↵
      1. Yarnitsky D,
      2. Bouhassira D,
      3. Drewes AM, et al
      . Recommendations on practice of conditioned pain modulation (CPM) testing. Eur J Pain 2015;19:805–6.doi:10.1002/ejp.605pmid:http://www.ncbi.nlm.nih.gov/pubmed/25330039
      OpenUrlPubMed
    95. ↵
      1. Suokas AK,
      2. Walsh DA,
      3. McWilliams DF, et al
      . Quantitative sensory testing in painful osteoarthritis: a systematic review and meta-analysis. Osteoarthritis Cartilage 2012;20:1075–85.doi:10.1016/j.joca.2012.06.009pmid:http://www.ncbi.nlm.nih.gov/pubmed/22796624
      OpenUrlCrossRefPubMedWeb of Science
    96. ↵
      1. Yarnitsky D,
      2. Arendt-Nielsen L,
      3. Bouhassira D, et al
      . Recommendations on terminology and practice of psychophysical DNIC testing. Eur J Pain 2010;14:339.doi:10.1016/j.ejpain.2010.02.004pmid:http://www.ncbi.nlm.nih.gov/pubmed/20227310
      OpenUrlCrossRefPubMedWeb of Science
    97. ↵
      1. Kennedy DL,
      2. Kemp HI,
      3. Ridout D, et al
      . Reliability of conditioned pain modulation: a systematic review. Pain 2016;157:2410–9.doi:10.1097/j.pain.0000000000000689pmid:http://www.ncbi.nlm.nih.gov/pubmed/27559835
      OpenUrlCrossRefPubMed
    98. ↵
      1. Parkitny L,
      2. McAuley JH,
      3. Walton D, et al
      . Rasch analysis supports the use of the depression, anxiety, and stress scales to measure mood in groups but not in individuals with chronic low back pain. J Clin Epidemiol 2012;65:189–98.doi:10.1016/j.jclinepi.2011.05.010pmid:http://www.ncbi.nlm.nih.gov/pubmed/21889306
      OpenUrlCrossRefPubMed
    99. ↵
      1. Osman A,
      2. Barrios FX,
      3. Gutierrez PM, et al
      . The pain Catastrophizing scale: further psychometric evaluation with adult samples. J Behav Med 2000;23:351–65.doi:10.1023/a:1005548801037pmid:http://www.ncbi.nlm.nih.gov/pubmed/10984864
      OpenUrlCrossRefPubMedWeb of Science
    100. ↵
      1. Wertli MM,
      2. Eugster R,
      3. Held U, et al
      . Catastrophizing-a prognostic factor for outcome in patients with low back pain: a systematic review. Spine J 2014;14:2639–57.doi:10.1016/j.spinee.2014.03.003pmid:http://www.ncbi.nlm.nih.gov/pubmed/24607845
      OpenUrlCrossRefPubMed
    101. ↵
      1. Roelofs J,
      2. Peters ML,
      3. McCracken L, et al
      . The pain vigilance and awareness questionnaire (PVAQ): further psychometric evaluation in fibromyalgia and other chronic pain syndromes. Pain 2003;101:299–306.doi:10.1016/S0304-3959(02)00338-Xpmid:http://www.ncbi.nlm.nih.gov/pubmed/12583873
      OpenUrlCrossRefPubMedWeb of Science
    102. ↵
      1. Price DD,
      2. McGrath PA,
      3. Rafii A, et al
      . The validation of visual analogue scales as ratio scale measures for chronic and experimental pain. Pain 1983;17:45–56.doi:10.1016/0304-3959(83)90126-4pmid:http://www.ncbi.nlm.nih.gov/pubmed/6226917
      OpenUrlCrossRefPubMedWeb of Science
    103. ↵
      1. Price DD,
      2. Bush FM,
      3. Long S, et al
      . A comparison of pain measurement characteristics of mechanical visual analogue and simple numerical rating scales. Pain 1994;56:217–26.doi:10.1016/0304-3959(94)90097-3pmid:http://www.ncbi.nlm.nih.gov/pubmed/8008411
      OpenUrlCrossRefPubMedWeb of Science
    104. ↵
      1. Deyo RA,
      2. Battie M,
      3. Beurskens AJ, et al
      . Outcome measures for low back pain research. A proposal for standardized use. Spine 1998;23:2003–13.doi:10.1097/00007632-199809150-00018pmid:http://www.ncbi.nlm.nih.gov/pubmed/9779535
      OpenUrlCrossRefPubMedWeb of Science
    105. ↵
      1. Dunn KM,
      2. Croft PR
      . Classification of low back pain in primary care: using "bothersomeness" to identify the most severe cases. Spine 2005;30:1887–92.doi:10.1097/01.brs.0000173900.46863.02pmid:http://www.ncbi.nlm.nih.gov/pubmed/16103861
      OpenUrlCrossRefPubMedWeb of Science
    106. ↵
      1. Kamper SJ,
      2. Maher CG,
      3. Mackay G
      . Global rating of change scales: a review of strengths and weaknesses and considerations for design. J Man Manip Ther 2009;17:163–70.doi:10.1179/jmt.2009.17.3.163pmid:http://www.ncbi.nlm.nih.gov/pubmed/20046623
      OpenUrlCrossRefPubMed
    107. ↵
      1. Herdman M,
      2. Gudex C,
      3. Lloyd A, et al
      . Development and preliminary testing of the new five-level version of EQ-5D (EQ-5D-5L). Qual Life Res 2011;20:1727–36.doi:10.1007/s11136-011-9903-xpmid:http://www.ncbi.nlm.nih.gov/pubmed/21479777
      OpenUrlCrossRefPubMedWeb of Science
    108. ↵
      1. Topp CW,
      2. Østergaard SD,
      3. Søndergaard S, et al
      . The WHO-5 well-being index: a systematic review of the literature. Psychother Psychosom 2015;84:167–76.doi:10.1159/000376585pmid:http://www.ncbi.nlm.nih.gov/pubmed/25831962
      OpenUrlCrossRefPubMed
    109. ↵
      1. Pascual-Marqui RD
      . Standardized low-resolution brain electromagnetic tomography (sLORETA): technical details. Methods Find Exp Clin Pharmacol 2002;24 Suppl D:5-12.pmid:http://www.ncbi.nlm.nih.gov/pubmed/12575463
      OpenUrlPubMed
    110. ↵
      1. Nichols TE,
      2. Holmes AP
      . Nonparametric permutation tests for functional neuroimaging: a primer with examples. Hum Brain Mapp 2002;15:1–25.doi:10.1002/hbm.1058pmid:http://www.ncbi.nlm.nih.gov/pubmed/11747097
      OpenUrlCrossRefPubMedWeb of Science
    111. ↵
      1. Pascual-Marqui RD
      . Discrete, 3D distributed, linear imaging methods of electric neuronal activity. Part 1: exact, zero error localization. arXiv2007.doi:10.48550/arXiv.0710.3341
    112. ↵
      1. Braun V,
      2. Clarke V
      . Using thematic analysis in psychology. Qual Res Psychol 2006;3:77–101.doi:10.1191/1478088706qp063oa
      OpenUrlCrossRef
    113. ↵
      1. Thomas DR
      . A general inductive approach for analyzing qualitative evaluation data. Am J Eval 2006;27:237–46.doi:10.1177/1098214005283748
      OpenUrl
    114. ↵
      1. Eldridge SM,
      2. Lancaster GA,
      3. Campbell MJ, et al
      . Defining feasibility and pilot studies in preparation for randomised controlled trials: development of a conceptual framework. PLoS One 2016;11:e0150205.doi:10.1371/journal.pone.0150205pmid:http://www.ncbi.nlm.nih.gov/pubmed/26978655
      OpenUrlCrossRefPubMed

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    Footnotes

    • Contributors Conceptualisation: DBA, DDR, RM, JR, and SV; Methodology/Design of the work: DBA, DDR, RM, JR and SV; Writing—original draft preparation: DBA, DDR and RM; writing—critically reviewing and revising: DBA, DDR, RM, SV and JR. All authors have critically read and agreed to the final version of the submitted manuscript and agree to be accountable for all aspects of the work.

    • Funding This work is supported by NZ Health Research Council (20/618), Healthcare Otago Charitable Trust (Grant number: N/A), Lottery Health Research (20959) and Brain Health Research Centre (Grant number: N/A).

    • Disclaimer The funding bodies were not involved in the study conceptualisation or design; and will not be involved in the collection, analysis, and interpretation of data; in the writing of the report; and in the decision to submit the article for publication.

    • Competing interests None declared.

    • Patient and public involvement Patients and/or the public were not involved in the design, or conduct, or reporting, or dissemination plans of this research.

    • Provenance and peer review Not commissioned; externally peer reviewed.

    • Supplemental material This content has been supplied by the author(s). It has not been vetted by BMJ Publishing Group Limited (BMJ) and may not have been peer-reviewed. Any opinions or recommendations discussed are solely those of the author(s) and are not endorsed by BMJ. BMJ disclaims all liability and responsibility arising from any reliance placed on the content. Where the content includes any translated material, BMJ does not warrant the accuracy and reliability of the translations (including but not limited to local regulations, clinical guidelines, terminology, drug names and drug dosages), and is not responsible for any error and/or omissions arising from translation and adaptation or otherwise.