Article Text

Original research
Scoping review to identify and map non-pharmacological, non-surgical treatments for dysphagia following moderate-to-severe acquired brain injury
  1. Signe Janum Eskildsen1,2,
  2. Ingrid Poulsen2,3,
  3. Daniela Jakobsen4,
  4. Christian Gunge Riberholt4,
  5. Derek John Curtis4,5
  1. 1Department of Occupational Therapy and Physiotherapy, Rigshospitalet, University of Copenhagen, Copenhagen, Denmark
  2. 2Research Unit of Nursing and Health Care, Health, Aarhus University, Aarhus, Denmark
  3. 3Department of Clinical Research, Copenhagen University Hospital, Rigshospitalet, Amager and Hvidovre, Denmark
  4. 4Department of Brain Injury, Rigshospitalet, University of Copenhagen, Copenhagen, Denmark
  5. 5Child Centre Copenhagen, The Child and Youth Administration, Copenhagen, Denmark
  1. Correspondence to Signe Janum Eskildsen; signe.janum.eskildsen{at}regionh.dk

Abstract

Introduction Dysphagia is a common and critical consequence of acquired brain injury (ABI) and can cause severe complications. Dysphagia rehabilitation is transforming from mainly compensatory strategies to the retraining of swallowing function using principles from neuroscience. However, there are no studies that map interventions available to retrain swallowing function in patients with moderate-to-severe ABI.

Objective To systematically map the accessible research literature to answer the research question: Which non-surgical, non-pharmacological interventions are used in the treatment of dysphagia in patients with moderate and severe ABI in the acute and subacute phase?

Design Scoping review based on the methodology of Arksey and O’Malley and methodological advancement by Levac et al.

Data sources MEDLINE, Embase, Cochrane Library, CINAHL, PsycINFO, Web of Science, OTseeker, speechBITE and PEDro were searched up until 14 March 2021.

Eligibility criteria All studies reporting rehabilitative interventions within 6 months of injury for patients with moderate-to-severe ABI and dysphagia were included.

Data extraction and synthesis Data was extracted by two independent reviewers and studies were categorised based on treatment modality.

Results A total of 21 396 records were retrieved, and a final of 26 studies were included. Interventions were categorised into cortical or non-cortical stimulation of the swallowing network. Cortical stimulation interventions were repetitive transcranial magnetic stimulation (rTMS) and transcranial direct current stimulation. Non-cortical were complex swallowing interventions, neuromuscular electrical stimulation, pharyngeal electrical stimulation (PES), sensory stimulation, strengthening exercises and respiratory muscle training.

Conclusion This scoping review provides an overview of rehabilitative dysphagia interventions for patients with moderate and severe ABI, predominantly due to stroke, in the acute and subacute phase. Positive tendencies towards beneficial effects were found for rTMS, complex swallowing interventions, PES and cervical strengthening. Future studies could benefit from clear reporting of patient diagnosis and disease severity, the use of more standardised treatment protocols or algorithms and fewer but standardised outcome measures to enable comparison of effects across studies and interventions.

  • rehabilitation medicine
  • therapeutics
  • neurological injury
  • stroke
  • quality in health care

Data availability statement

All data relevant to the study are included in the article or uploaded as supplementary information.

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/.

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Strengths and limitations of this study

  • An extensive search in multiple databases and subsequent consultation with key informants led to an exhaustive mapping of rehabilitation approaches in neurogenic dysphagia.

  • Data extraction variables thoroughly described the study sample, intervention, control, timing and dose, outcome measures and results reported.

  • A categorisation for included interventions is used to map dysphagia rehabilitation based on stimulation site of the swallowing network.

  • There was no quality assessment of the included studies; however, a summary of reported results from studies divided in subcategories is presented.

Introduction

Dysphagia (swallowing disorder) is a common and critical consequence of acquired brain injury (ABI).1–5 Dysphagia can impact the general health and the consequences of swallowing disability are severe, causing either impaired efficiency, safety of the swallow or both. Impaired efficiency can lead to dehydration, malnutrition and weight loss, while impaired safety can cause laryngeal penetration of saliva, food or liquid or tracheobronchial aspiration that may cause pneumonia, or lead to choking and death.1 4 6 7 The incidence of dysphagia is reported as high as 93% following severe brain injury.8 Dysphagia can prolong hospital length of stay and is associated with significantly higher healthcare costs of up to 40%, regardless of whether the patient develops pneumonia.9 10

Dysphagia is recognised by the WHO as a medical disability, having profound psychological and social consequences for the individual, impacting negatively on quality of life.11 12 Difficulty swallowing can cause frustration, anxiety and embarrassment during mealtimes, especially at social events where eating should be pleasurable and may result in the individual becoming less active and participating less in society.12 13

The clinical presentation of swallowing impairment is dependent on the origin and type of ABI, and may be caused by sensory and/or motor deficits.14 Swallowing is a multifaceted process requiring interaction and coordination of conscious and autonomous responses with precise coordination of multiple muscle groups in the oral cavity, pharynx and larynx.15 Swallowing is coordinated mainly by a swallowing centre, an interneuronal network centred in the brain stem, receiving peripheral sensory inputs from the pharynx and larynx and central inputs from the cortex.16 Any damage to the neurophysiological pathway can result in dysphagia, caused by a loss of functional connectivity within the neural swallowing network.

Patients with severe brain injuries are not always able to actively participate in exercises or change of behaviour for safe swallowing techniques in rehabilitation of swallowing and eating function, due to sensorimotor, perceptive, cognitive dysfunctions or impaired consciousness. Thus, following instructions for exercises, behavioural adjustments and self-training is not an option and limits the choice of intervention.

Scientists and clinicians have long been occupied and concerned about how to treat dysphagia and to transfer knowledge about neuroplasticity and motor learning from movement science and neuroscience into the recovery of swallowing function.17 Several reviews have addressed dysphagia rehabilitation using specific approaches or within limited diagnosis groups of ABI,18–21 but none have offered a more comprehensive overview. For further details, please see the published protocol.22 Many unanswered questions remain when it comes to choosing the adequate treatment approach, dose and intensity for different populations suffering from dysphagia. There is no clear evidence or consensus about when to compensate or retrain swallowing function or assessment of whether an intervention is applicable in the clinical setting.17 23 24 However, the paradigm for dysphagia treatment is changing from compensatory strategies, such as modified consistencies for food and liquid and postural changes, to the recovery and re-training of swallowing function relying on neuroscientific results.10 23 24

Research, especially in patients with severe brain injury is sparse.25 Still, the consequences of dysphagia might be devastating for the patient’s quality of life, level of activity and participation and lead to a massive burden for caregivers and the healthcare systems. Thus, the long-term goal of dysphagia rehabilitation is to re-establish safe swallowing and eating function and protection of airways for maximal activity and participation in daily life.

Review objective

The objective of this scoping review is to systematically map the accessible research literature to answer the research question: Which non-surgical, non-pharmacological interventions are used in the treatment of dysphagia in patients with moderate and severe ABI in the acute and subacute phase?

Methods

The study is designed and conducted in accordance with the Preferred Reporting Items for Systematic reviews and Meta-Analysis extension for Scoping Reviews (PRISMA-ScR) reporting guidelines.26 The protocol for this scoping review has been published earlier.22

A scoping review approach based on the methodology by Arksey and O’Malley and methodological advancement by Levac et al was applied.27 28 This method allows for an elaborate search of the literature and the broad scope of the research subject. The method entails six stages of the scoping review process: (1) identifying the research question; (2) identifying relevant studies; (3) selecting studies; (4) charting the data; (5) collating, summarising and reporting the results and (6) consulting with relevant stakeholders.28 Stage 1 is described in detail in the published protocol.22

Stages 2 and 3: identifying and selecting relevant studies

Database selection and search strategy

We searched the following electronic bibliographic databases: MEDLINE (Ovid); Cochrane Central Register of Controlled Trials (CENTRAL, The Cochrane Library); Embase (Ovid); CINAHL (EBSCO); PsycINFO; Science Citation Index Expanded on Web of Science; OTseeker; speechBITE; and PEDro.

The search strategy included terms related to the condition and population. Specific keywords identified in the preliminary search were introduced in the final search strategy. The search strategy for MEDLINE (the preliminary) was adapted for searches in all other databases (online supplemental appendix 1).

References of relevant adjacent reviews and included papers were screened for further relevant studies.

Furthermore, we searched for ongoing and unidentified clinical trials on:

Google Scholar; Database on Research in Stroke (DORIS); The Turning Research into Practice (TRIP) Database; ClinicalTrials.gov; EU Clinical Trial Register; Chinese Clinical Trial Registry (ChCTR); International Standard Randomised Controlled Trial Number (ISRCTN) registry; Pan African Clinical Trials Registry (PACTR); Australian New Zealand Clinical Trials Registry (ANZCTR); Clinical Trials Registry—India (CTRI); and the WHO International Clinical Trials Registry Platform (ICTRP) search portal.

Asian language studies were excluded as acceptable translation was not possible. There was no restriction on publication date.

The electronic search was based on patient characteristics and did not include search terms for any treatment or intervention, thus reducing the risk of excluding relevant studies. The final search was conducted on 14 March 2021, by two authors (SJE and DJC). All five authors were included in the development of the search strategy and approved the final version. Search results were imported for screening and further reviewing in Covidence systematic review software 2020, Veritas Health Innovation, Melbourne, Australia, where duplicates were identified and removed.

Studies of any design on rehabilitative, non-surgical, non-pharmacological treatment for patients of all ages with moderate-to-severe ABI with dysphagia in the first 6 month from injury were eligible for inclusion.

The following criteria for moderate-to-severe ABI was used; The National Institute of Health Stroke Scale (NIHSS) >15; Glasgow Coma Scale (GCS) <922; Barthel Index <60; Functional Independence Measure (FIM) ≤54; Modified Rankin Scale (MRS) ≥4.29

Corresponding authors of studies that could not be assessed for eligibility due to missing data on brain injury severity were contacted to obtain this information.

Three authors (SJE, IP and DJC) independently screened title and abstracts of all retrieved citations against the detailed inclusion and exclusion criteria.22 If disagreement occurred, consensus was achieved through discussion between the four authors (SJE, DJ, IP and DJC). Prior to screening n=30 title and abstracts were reviewed to ensure agreement on interpretation of the eligibility criteria and approach to screening.

Three authors (SJE and DJC) independently extracted prespecified data from included studies in a chart based on the protocol. Two reviewers verified each extraction. DJ extracted data from German language studies.

Stages 4 and 5: charting the data, collating, summarising and reporting the results

Data on: general information (title, authors, country, contact information, year, language); methods (design, setting); interventions (type, timing, dose, duration, control if any); participants (n, demographics); and outcome measures was extracted and collected in a table.

The studies were categorised based on treatment modality as well as subgroup diagnosis and age-group, (paediatric (0–17 years) and adults, respectively). Treatment interventions were categorised in two main categories based on previous literature: (1) interventions that used direct brain stimulation (cortical); (2) interventions that used indirect brain stimulation (non-cortical)18 and divided into subgroups based on the type of intervention.

In addition, outcome measures used in included studies are presented, as well as the reported results from the studies. First, a numeric analysis was conducted and second, a qualitative descriptive analysis of the findings.

Stage 6: consultation with stakeholders

The Danish Society for Dysphagia, the European Society for Swallowing Disorders (ESSD), the Society of Occupational Therapy for Dysphagia (DK), as well as key informants Rainer Seidl (Germany), Olle Ekberg (Sweden), Renée Speyer (Norway) and Ulrike Frank (Germany) were contacted by mail to identify potential missing or ongoing relevant studies or interventions that were not retrieved in the review process.

Patient and public involvement

There has been no patient or public involvement in addition to the key informants.

Results

A total of 21 396 records were retrieved from database searches. Additional searches produced no new records, and consultation with stakeholders produced 33 additional records. After removing duplicates, 16 180 abstracts were screened for eligibility and subsequently 344 articles were assessed in full-text. Due to language restrictions, 61 studies were excluded. Corresponding authors of 73 studies were contacted, where the ABI severity was not stated. None of the inquiries yielded further information on severity and we therefore chose to exclude these studies. A final 26 studies were included. Figure 1 PRISMA flowchart.

Figure 1

Preferred Reporting Items for Systematic reviews and Meta-Analysis flowchart. awere unable to assess eligibility, bawaiting classification

Of the 26 included studies and trials, 18 are randomised controlled trials (n=10 to n=306),30–47 one is a non-randomised controlled trial (n=24),48 three are cohort studies (n=24 to n=208),8 49 50 two are case series51 52 and two are case reports.53 54 The studies are published between 1998 and 2020.

Numerical analysis

Table 1 presents the characteristics of included studies in detail.

Table 1

Included studies

The 26 studies had a total of 1601 patients included. In 17 studies the patients had dysphagia following stroke.31–34 36–42 44–46 48 52 Three studies included only patients with traumatic brain injury (TBI)8 30 54 and four included patients with stroke and patients with TBI.35 43 47 51 53 Bath et al also included patients with both stroke and TBI, but only the TBI subgroup met our inclusion criteria and was included.49 One study also included patients with head and neck cancer and degenerative neurological diseases in addition to acute ABI.50 All studies were set in a hospital or acute or subacute rehabilitation units.

One study included children with ABI (n=60),30 the remaining included adults with ABI.

Studies were conducted in Germany (n=5), Korea (n=3), Denmark (n=2), Egypt (n=2), Australia (n=1), China (n=1), Greece (n=1), Iran (n=1), Italy (n=1), Japan (n=1), Spain (n=1), Sweden (n=1), Taiwan (n=1), Thailand (n=1), UK (n=1), USA (n=1), one multicentre cohort study included patients in Austria, Germany and the UK, and a multicentre RCT included patients in Austria, Germany and Italy.

The swallowing assessment used as the inclusion criterion varied between studies: 5 studies used clinical assessment,30 39 46 47 52 2 studies used a dysphagia screening tool,34 45 2 studies based inclusion on oral intake38 42 and 16 studies used instrumental assessment by fibreoptic endoscopic evaluation of swallowing or Videofluoroscopic Swallow Study.31–33 35–37 40 41 43 44 47–51 54 One study did not report on the method for initial dysphagia assessment.53

Qualitative syntheses

The interventions can be categorised into the two main treatment modalities, cortical or non-cortical stimulation of the swallowing network (figure 2).

Figure 2

Categorisation of swallowing therapy interventions in included studies.

Cortical interventions

Two interventions were defined as cortical stimulation interventions: Repetitive transcranial magnetic stimulation (rTMS), and transcranial direct current stimulation (tDCS). Cortical stimulation interventions are aimed at direct cortical stimulation of the brain and subcortical swallowing network. rTMS modulates cortical excitability by focally stimulating the cortical region. The studies in this review used rTMS to stimulate specific cortical motor areas associated with swallowing. The studies applied rTMS in varied modes. Khedr et al used 3 Hz rTMS on the oesophageal cortical motor area of the affected hemisphere34 and Lee et al applied 10 Hz to the cortex representing the suprahyoid muscle of the affected side.48 The remaining three studies targeted the mylohyoid muscles, with Tarameshlu et al applying 1 Hz to the undamaged cerebral hemisphere,42 Kim et al tested 5 Hz to the affected hemisphere35 and Park et al using 10 Hz bilaterally.37

Non-invasive tDCS is a cortical stimulation technique aimed at the recovery of swallowing functions by expansion of the pharyngeal representation in the undamaged hemisphere, hypothetically ensuring increased input to the brainstem swallowing centres. Current stimulation aims to facilitate this process in patients with hemispheric lesions without brainstem damage.36 39 One study applied anodal tDCS over the lesioned hemisphere and cathodal stimulation to the contralesional, aiming to restore output from the lesioned side and counteract a suppressive effect from the contralesional hemisphere.39 The second study used anodal tDCS to the unaffected hemisphere.36 The stimulation was applied during concurrent swallowing therapy.36 39

Non-cortical interventions

Non-cortical interventions are treatments aimed at improving swallowing by augmenting sensory input to the swallowing network in the brain, causing increased activity in the motor swallowing areas in the cortex, neural network and brain stem.18

Six categories were defined for mapping the non-cortical interventions: complex swallowing interventions, neuromuscular electrical stimulation (NMES), pharyngeal electrical stimulation (PES), sensory stimulation (including sensory electrical stimulation (SES), thermo-stimulation and thermal/tactile stimulation), strengthening exercises and respiratory muscle training.

Three studies combined interventions consisting of direct exercises and/or manoeuvres and compensation strategies, including positioning, posture change and dietary modification.30 32 44 Swallowing exercises aim at altering swallowing physiology and promoting long-term changes, and can involve strengthening impaired oropharyngeal musculature through oropharyngeal exercise, using oropharyngeal swallowing manoeuvres (some are both a compensatory strategy and rehabilitative exercise), and increase sensory input through thermal–tactile stimulation.55 56 Carnaby et al tested the intervention at low and high intensity against usual care,32 while Xia et al tested acupuncture as an add-on to a combined intervention.44 Three descriptive case studies examined Facial Oral Tract Therapy (F.O.T.T.), an interdisciplinary complex rehabilitation intervention that aims to re-establish facial oral functions in everyday life activities, using principles for motor learning.57–59 One pilot RCT study tested the effect of intensified non-verbal facilitation of swallowing during F.O.T.T.47 and one study examined the effect of F.O.T.T. on time to unrestricted diet in a cohort.8

Two studies tested NMES,38 43 a treatment used to strengthen muscle groups with preserved motor innervation, targeting strengthening of the oropharyngeal musculature to improve swallowing physiology. It is also hypothesised to provide sensory feedback to the central nervous system to facilitate swallowing response.60 Terré and Mearin placed electrodes horizontally in the submental region over the mylohyoid muscle (suprahyoid) with the lower set placed on the skin either side over the thyroid cartilage.43 Permsirivanich et al described the electrode placement as ‘midline 1 mm above the thyroid notch, the second electrode immediately superior to the first, the third electrode 1 mm below the thyroid notch and the fourth electrode immediately inferior to the third’. The strength of stimulation was “based on the subjects’ verbal feedback’.38 Both NMES studies used a stimulation frequency of 80 Hz.

PES was tested in four studies.31 33 41 49 Like NMES, PES targets the peripheral neuromuscular system and aims to strengthen the impaired oropharyngeal musculature. In two studies, patients had tracheostomies, and decannulation was the main outcome.33 41

In two studies, different sensory stimulation interventions were assessed.50 52 Hamada et al studied surface SES in combination with general dysphagia therapy. Electrodes were placed horizontally in the submental region over the mylohyoid muscle above the hyoid bone. The amplitude of the electrical current was set to the sensory threshold level at which the patients reported a tingling sensation on the skin.52 Hypothetically SES induces neuroplastic changes in the sensory cortex, but the exact mechanism is unknown.52 Prosiegel et al assessed thermo-stimulation combined with change of position, modification of consistencies and tongue exercises.50 The intervention aimed to trigger the swallowing reflex through thermo-stimulation.

One study tested an intervention of cervical strengthening exercises against resistance in four directions.40 The treatment aimed to improve posture by keeping the head in alignment in an upright position, the shoulders horizontal and activating muscles of mastication. Another study tested oral neuromuscular training with an oral device (Muppy) aimed at stimulating sensory input and strengthening the facial, oral and pharyngeal muscles.45

The final study was categorised as respiratory muscle training (RMT) with a hand-held threshold trainer and investigated the feasibility and efficacy of a combined inspiratory and expiratory muscle training on pulmonary dysfunction and swallowing function.46

The outcome measures of the studies are categorised and presented in table 2.

Table 2

Dysphagia outcome measures applied in included studies

Summary of reported results by intervention subcategories

Four studies on rTMS with sham control groups found some improvement in favour of the intervention,34 35 37 48 the remaining study on rTMS found a better effect of rTMS combined with traditional dysphagia therapy than rTMS or traditional therapy alone.42 Results on tDCS are inconsistent. One shows effect on Dysphagia Outcome Severity Scale (DOSS) compared with sham, the other no difference between groups on DOSS or Penetration Aspiration Scale (PAS).36 39

For the complex swallowing interventions using combined exercise and compensatory intervention, the results are also inconsistent. Carnaby et al found no significant difference between groups,32 while the study by Abusaad and Kassem showed an improvement in feeding domains for children after a 1-month intervention.30

Three studies on F.O.T.T. were case studies/series that found increased oral intake and improved safety of swallowing.51 53 54 Hansen et al also found improvement in oral intake using Functional Oral Intake Scale (FOIS) in a retrospective cohort.8 Jakobsen et al found improved scores for PAS and FOIS in both groups, but no significant difference between groups after non-verbal facilitation of swallowing in an RCT.47 Xia et al found no difference at the end of treatment for acupuncture as an add-on to standard dysphagia therapy, but did find a significant difference in favour of the intervention group with improvement in dysphagia severity at 4 weeks follow-up.44

Overall, the two RCT studies on NMES found no difference between intervention and control, but both had active control groups.38 43

Of the three RCT studies on PES, two found effect on decannulation,33 41 the third found no difference between intervention and control on PAS.31 Bath et al found significant improvement from baseline to 3-month post-PES treatment on the Dysphagia Severity Rating Scale for 20 patients in a per-protocol analysis in a subsample of patients with TBI.49

The two studies on sensory stimulation and conventional dysphagia therapy reported mixed results.50 52 Hamada et al found fewer pulmonary infections after SES in a retrospective cohort study.52 Prosiegel et al found positive changes in oral intake and decannulation after thermo-stimulation in a prospective cohort study.50

The RCT study on cervical strengthening exercises found improved oral intake at end of treatment (12 weeks)40 and the RCT study from Hägglund et al found that oral neuromuscular training using an oral device (Muppy) improved swallowing rate at 1 year, but not at 5 weeks follow-up.45

Liaw et al found no significant difference between the groups over time on FOIS in an RCT comparing regular rehabilitation with and without RMT.46

Discussion

This scoping review presents a summary of rehabilitative dysphagia interventions reported in the literature in patients with moderate-to-severe ABI. We identified two major categories of interventions, cortical and non-cortical stimulation and eight subcategories based on treatment modality: rTMS; tDCS; complex swallowing interventions; NMES; PES; sensory stimulation (including SES, thermo-stimulation and thermal/tactile stimulation), strengthening exercises and respiratory muscle training.

A scoping review was chosen in preference to a systematic review to ensure a broad scope in a sparse research field and because we wished to include all study types and designs as well as grey literature, in order to identify all the relevant interventions that have been published.61 We could also see great value in the validation and consulting stage with key experts in the field, which did in fact lead to the inclusion of additional studies.

We chose to categorise the interventions identified in this review in a similar way to those in the most recent Cochrane review (2018) on swallowing therapy for dysphagia in acute and subacute stroke.18 Unlike the Cochrane review, we did not include studies on patients with mild injuries. Nevertheless, some of the interventions investigated in the Cochrane review that do not require active participation were also included in this scoping review. Furthermore, we chose to include all study designs as our focus was not on the effect of treatment. Instead, we scoped the field of dysphagia interventions, and found additional categories of complex swallowing interventions, that were not examined in the above-mentioned Cochrane review. Our review identifies additional studies focusing on strengthening exercises, complex dysphagia interventions and studies that have been published after 2018.

Many of the interventions identified in this review (rTMS, tDCS, NMES, PES, SES, oral neuromuscular training, RMT) require purchase of specific equipment and specialised training for correct and safe performance. Training requirements and equipment cost can be a barrier to the implementation of these interventions in routine clinical practice.

It is apparent from the included studies that any form of evidence synthesis would be difficult. The interventions not only vary in intensity and duration but also in the nature of the intervention, for example, placement of electrodes, stimulation frequency, intensity and mode. Usual treatment is used in many studies with the study intervention as an add-on. Usual treatment is often described by a list of interventions with no description of the dose, intensity, application or timing of the different components. Future studies should emphasise the description of standard care.

Outcome measures are also diverse and may reflect the rehabilitation phase, injury severity or even the setting. In order to allow for a meaningful evidence synthesis, there is a need to establish consensus on reliable and valid core outcomes for dysphagia in this population.

Furthermore, observational studies are prone to overestimate the effect size.62 Even those studies showing an effect should be interpreted with caution.

Many studies do not report brain injury severity but only dysphagia severity. This makes it difficult to assess the applicability and effect of the intervention on a given patient and could complicate or hinder implementation of an intervention in the clinical setting. For example, some of the included interventions require the patients’ active participation in performing specific exercises. This would exclude patients with severe ABI and disorders of consciousness. The effect of the intervention may also vary between patients with moderate and severe brain injury and be depended on the type of injury. These details should be consistently reported in future studies, along with patient characteristics on consciousness, cognition and participatory ability.

Strengths and limitations

This review has several limitations. First, missing data on brain injury severity in several studies led to excluding some possibly relevant studies. This information was often unavailable from the corresponding authors. Second, the timing of the assessment of brain injury severity was often not reported or consistent between studies, making it difficult to determine whether the study met the inclusion criteria. Third, the limitations due to necessary language restrictions caused the exclusion of Asian language papers, potentially excluding some relevant studies. Finally, given that the included studies have not been quality assessed, the summarisation of results should be interpreted with caution and cannot be directly applied to guide clinical practice.

The major strength of the scoping review is a comprehensive search, screening and selection of the literature using rigorous and transparent methods guided by the previously published protocol based on well-established methodology.63 The review also included a comprehensive consultation process to ensure no relevant studies were overlooked.

Conclusion

This scoping review provides an overview of which non-surgical, non-pharmacological interventions are used in the rehabilitation of dysphagia in patients with moderate and severe ABI, predominantly patients who had a stroke, in the acute and subacute phase. Identifying two major categories of interventions, cortical and non-cortical stimulation and eight subcategories based on treatment modality: rTMS; tDCS; complex swallowing interventions; NMES; PES; sensory stimulation; strengthening exercises; and respiratory muscle training. Positive tendencies towards beneficial effects were found for rTMS, F.O.T.T, PES and cervical strengthening, although many of these studies are observational or case reports. Although not comparable across studies, results favoured rTMS over sham, case studies on F.O.T.T. showed improved swallowing safety and increased food intake, as did cervical strengthening exercises, while PES was found to improve time to decannulation. Results on tDCS and complex interventions were inconsistent, while studies on NMES and RMT found no difference between intervention and control. It is evident from the included studies, that any form of evidence synthesis would be difficult. Thus, based on this scoping review, we cannot recommend conducting a systematic review until further research is available. Future studies of rehabilitative interventions for dysphagia could benefit from clear reporting of patient diagnosis and disease severity, the use of more standardised treatment protocols or algorithms and fewer but standardised outcome measures to enable comparison of effects across studies and interventions.

Differences between protocol and review

Some adjustments to the selection criteria were required. The protocol stated no language restrictions, however, it was not possible to get an acceptable translation for the studies in Asian languages and consequently they were excluded. Not all studies reported brain injury severity, thus, the research group discussed additional cut-off values for determining severity by searching the literature. In addition to the NIHSS score and GCS already defined in our protocol article,22 the following measures and definitions on severity were included: Barthel Index <60, FIM ≤54 and MRS≥4.29 We did not state in our protocol how to assess studies that did not report brain injury severity. We decided to exclude studies in which brain injury severity could not be determined after contact to the corresponding author. Finally, we stated that two reviewers would independently extract data, however we changed this to one reviewer, and the data extraction was subsequently confirmed for accuracy by another reviewer.

Data availability statement

All data relevant to the study are included in the article or uploaded as supplementary information.

Ethics statements

Patient consent for publication

Acknowledgments

Thank you to all key informants for excellent feedback and for taking the time to respond and comment on our results. A special thanks to Rainer Seidl, Ulrike Frank, Olle Ekberg, Tina Hansen, Trine Schow and Annette Kjærsgaard. Thank you to corresponding authors for their efforts to try to provide data on brain injury severity and to Linnea Larsen for her valuable contributions in the initial stages of the study.

References

Supplementary materials

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Footnotes

  • Contributors DJC and DJ are responsible for the conception of the study. SJE, DJ, CGR, IP and DJC contributed to the development of the design. SJE, DJC and IP screened citations, reviewed full-text articles and achieved consensus on the final included studies. SJE and DJC extracted the data, and DJ extracted data from German language studies. All authors contributed to the development of categories. SJE and DJC drafted the manuscript. All authors provided important intellectual contribution and guidance throughout the development of the manuscript. All authors contributed, edited and approved the final version of this manuscript. DJC ans SJE acted as guarantors.

  • Funding This research received no specific grant from any funding agency in the public, commercial or not-for-profit sectors. We gratefully acknowledge the support of our workplace, Rigshospitalet, Department of Occupational Therapy and Physiotherapy and Department of Brain Injury.

  • Competing interests None declared.

  • 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.

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