Transient neurological symptoms in the older population: report of a prospective cohort study—the Medical Research Council Cognitive Function and Ageing Study (CFAS)

Objective Transient ischaemic attack (TIA) is a recognised risk factor for stroke in the older population requiring timely assessment and treatment by a specialist. The need for such TIA services is driven by the epidemiology of transient neurological symptoms, which may not be caused by TIA. We report prevalence and incidence of transient neurological symptoms in a large UK cohort study of older people. Design Longitudinal cohort study Setting The Medical Research Council Cognitive Function and Aging Study (CFAS) is a population representative study based on six centres across England and Wales. Participants Random samples of people in their 65th year were obtained from Family Health Service Authority lists. The participation rate was 80% (n=13 004). Interview at baseline included questions about stroke and three transient neurological symptoms, repeated in a subsample after 2 years. Patients were flagged for mortality. Main outcome measures Prevalence and 2-year incidence of transient neurological symptoms. Results In 11 903 participants without a history of stroke, 271 (2.3%) reported transient problems with speech, 872 (7.6%) with sight and 596 (5.1%) weakness in a limb with 1456 (12.7%) reporting at least one symptom. Of those reinterviewed (n=6748), 675 (9.8%) reported at least one symptom over 2 years. Conclusions Lifetime prevalence and incidence of transient neurological symptoms in people aged 65 years and over is high and is substantially greater than the incidence of TIA in hospital-based and population-based studies. These high rates of transient neurological symptoms in the community in the older population should be considered when planning TIA services.


THE STUDY
Supplemental documents are adequate, do not contain information that would be better reported in the manuscript, and do not raise questions about the work.

GENERAL COMMENTS
Nahal and colleagues have conducted an interesting populationbased analysis of the incidence of transient neurological symptoms among older individuals in the UK using data collected from a large prospective cohort in the 1990s. The sampling methods are wellvalidated, the manuscript is clearly written, and the conclusions are well-tempered in the context of known limitations identified by the authors. A relatively high incidence of these transient neurological symptoms may have implications on future TIA referrals, though this speculation on this point goes beyond the scope of the current study.
The wording of the instrument that was used to elicit the transient neurological symptoms may not be ideal: Each symptom question actually contains multiple criteria--the symptoms must have been "sudden" AND have lasted for "less than a day" for example. These compound choices for each symptom increase the possibility of misinterpretation--particularly when a "yes" implies satisfying ALL criteria (including length and suddenness of onset of symptoms-rather than just one of these criteria. However, since the instrument was administered by a trained interviewer, rather than by using simple questionnaire for self-report, could mitigate this issue. Any available information on the characteristics of these question during pre-testing of the instrument would be enlightening. One interesting analysis that is not included in the present study, would be to look for an association between these transient neurological symptoms GENERAL COMMENTS CFAS provides a good opportunity to examine the incidence and prevalence of transient neurological symptoms (TNS) in UK older people, especially as there is a paucity of previous research in this area. The limitations of the study are due to the questions asked and the methodology of the surveys. However I do have the following suggestions to improve the clarity and interpretation of the paper.
1. It could be made more explicit, particularly in the abstract, that the study asked only about three TNS. Although this is mentioned in the "limitations section", it is also relevant to the discussion when findings are compared to other studies that included a wider range of symptoms.
2. I think there should be less focus on the findings being directly relevant to supply of TIA services. For example visual symptoms do not feature in campaigns such as FAST and so may not present more often to medical services as a result of publicity. Furthermore, it is likely that many of the symptoms reported here would not be referred as possible TIA if they presented to primary care (for example there is no distinction between unilateral and bilateral).
3. Some of the text included in Results (page 10) is speculative and would be better placed in the discussion section.
4. In the first para of discussion, it would be worth emphasising that incidences in Oxvasc are cases presenting to medical services.
5. References 6 and 27 are the same.

VERSION 1 -AUTHOR RESPONSE
Dr. Kim 1. "A relatively high incidence of these transient neurological symptoms may have implications on future TIA referrals, though this speculation on this point goes beyond the scope of the current study." We have revised the abstract and conclusions to reduce reference to predicted future increased need for TIA services.
2. The wording of the instrument that was used to elicit the transient neurological symptoms may not be ideal: Each symptom question actually contains multiple criteria--the symptoms must have been "sudden" AND have lasted for "less than a day" for example. These compound choices for each symptom increase the possibility of misinterpretation--particularly when a "yes" implies satisfying ALL criteria (including length and suddenness of onset of symptoms--rather than just one of these criteria. However, since the instrument was administered by a trained interviewer, rather than by using simple questionnaire for self-report, could mitigate this issue. Any available information on the characteristics of these question during pre-testing of the instrument would be enlightening.