Published online before print July 17, 2003, doi: 10.1161/01.STR.0000085294.27928.24
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(Stroke. 2003;34:e141.)
© 2003 American Heart Association, Inc.
Research Report |
Editorial Comment—Stroke Following TIA: Mounting Evidence of Early Risk
Davis Medical Center, University of California, Davis, Sacramento, California
TIAs are common events: a prevalence of 2.3% for a physician-rendered diagnosis of TIA was recently reported among US adults in a large community-based survey, equivalent to an estimated 4.9 million Americans carrying this diagnosis. An equal or greater number may have experienced an undiagnosed TIA.1
Patients with TIAs are at significant short-term risk of stroke, ranging from 4% to 8% in the first month,2 with an immediate risk of 5% in the first 2 days.3 Of those experiencing a stroke after a TIA, 21% will do so within the first month.4 Early evaluation of these patients seems prudent, but the urgency depends on an accurate determination of early risk since hospital admission of all TIA patients is likely to be financially prohibitive.5
The present report adds to previous data showing an early risk of stroke after TIA. The authors reanalyze data collected between 1981 and 1986 in the Oxfordshire Community Stroke Project (OCSP)6 which prospectively followed a population of patients presenting to their primary care provider with a TIA and/or completed stroke. The OCSP was a rigorously conducted study based on a clinical evaluation of each subject by a study neurologist with access to complete medical records throughout the course of the study.7 It is one of the few prospective studies of outcome following TIAs in nonhospitalized patients.8
The original OCSP study6 reported a moderate 4.4% risk of stroke in the first month following a recent TIA. In the present study, the authors recalculate this risk and suggest that it is much higher than the initial estimate: 8.6% and 12.0% at 7 and at 30 days, respectively. These conflicting results can be explained by a major change in the definition of the index TIA: the original OCSP study reported stroke rate following the most recent TIA and excluded those patients who presented with a stroke which had been preceded by a TIA. The present report calculates the risk of stroke after a first-in-lifetime TIA occurring at any time during the 5 years of the study, and includes patients presenting with stroke preceded by a TIA. Including such patients in the analysis doubles the 7-day risk of stroke after TIA from 4.2% to 8.6%. This dramatic difference in estimated risk demonstrates the extreme sensitivity of predictive models of TIA outcome on study design and inclusion criteria. The authors of the original OCSP study6 made a strong case for excluding these same patients so as not to unfavorably bias outcome predictions.
It would be most appropriate to include patients presenting with strokes following a TIA in a study defining the natural history of TIAs in the general community: in that case, all outcomes following the TIA would be relevant irrespective of the mode of presentation to medical attention. From a health care system perspective, however, where the risk to a defined population (eg, those presenting with TIA, not with a stroke) is sought, inclusion of such patients seems less justifiable.
Does the present study report the natural history of TIAs in the general community? Although it is labeled a "community-based" study to distinguish it from hospital-based ones, it actually evaluates a selected population reporting a stroke or TIA to their primary care provider. Such a design does not capture patients who fail to recognize the symptoms of TIA or who do not report them to medical attention. The number of such patients is likely to be sizable: in a recent survey of American adults,1 only 8.6% could identify a symptom associated with a TIA, and more than half of those experiencing symptoms of TIA never reported them to medical attention. Citizens of the United Kingdom did no better: in a previous publication by the OCSP investigators, 54% of patients who experienced a TIA preceding their stroke did not report it to medical attention until after their stroke.9
Other methodological details of the study are worth noting: the index TIA may have preceded referral to the study by up to 5 years. While the median time from the first-ever TIA to study referral was a very reasonable 7 days, 14% of all patients were entered into the study 3 or more months after their TIA, and some after more than 18 months. Recall bias is likely to play a role in some of these patients: in a recent survey, only 39% of individuals recalling a physician diagnosis of TIA actually had such a diagnosis in their medical records, but only 55% of those with such a diagnosis in their records recalled the event.1 As pointed out by the authors, the meticulous methods used to confirm TIAs by the OCSP investigators is likely to minimize such source of inaccuracies. Finally, these data were collected up to 21 years ago; medical care has changed significantly since that time and the applicability of these findings to the current population is uncertain.
Despite the methodological controversies which are inevitably raised in the study of such ephemeral events, the 2-day risk of stroke following a TIA reported in this study is nearly identical to the risk reported by Johnston et al in patients presenting to an emergency department (5.1% versus 5.3%).3 Both are estimates of stroke risk in a selected population of TIA patients presenting to outpatient medical attention. For such patients the current study adds to the mounting evidence of an early risk of stroke which warrants rapid evaluation and treatment. The risk in the general population experiencing a TIA may be lower due to the potentially large number of patients who do not report their symptoms: determination of this risk awaits the results of further studies.
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2. Feinberg W, Albers G, Barnett H, Biller J, Caplan L, Carter L, Hart R, Hobson R, Kronmal R, Moore W, et al. Guidelines for the management of transient ischemic attacks. Circulation. 1994; 89: 2950–2965.
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9. Dennis M, Bamford J, Sandercock P, Warlow C. Incidence of transient ischemic attacks in Oxfordshire, England. Stroke. 1989; 20: 333–339.
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