How Do You Estimate Stroke Risk After a Transient Ischemic Attack?

April 24, 2007

BrainBy: Alana Choy-Shan, MD PGY-3
Transient ischemic attacks (TIAs) are known to be a harbinger of stroke, however it is difficult for physicians to estimate individual stroke risk. Previously, the two systems used to predict short-term risk of stroke after a TIA were the California and ABCD scores. Both scores are based on clinical factors with several key elements in common. However, neither scoring system was devised to predict stroke within 48 hours of TIA, a time period which may be most clinically relevant.

In this study[1] published in the Lancet in January, the creators of the California and ABCD scores tested a new system, called the ABCD2 score. In this scoring system, patients receive points for five factors including: age greater than or equal to 60 years (1 point); first recorded blood pressure after TIA with a systolic greater than or equal to 140mmHg or diastolic greater than or equal to 90mmHg (1 point); clinical features of TIA, unilateral weakness (2 points) or speech impairment without weakness (1 point); duration of TIA, greater than or equal to 60 minutes (2 points) or 10-59 minutes (1 point); and diabetes (1 point). The scoring system was validated in patients recruited from emergency departments, specialty and primary care clinics in California and Oxford. It was found to be a more accurate predictor of stroke than either the California or the ABCD scores. The 2 day risk of stroke after TIA was 0% for patients with an ABCD2 score of 0-1, 1-2% for a score of 2, 0-3% for a score of 3, 2-5% for a score of 4, 3-7% for a score of 5, 4-14% for a score of 6, and 0-50% for a score of 7. Stroke risk at 7 and 90 days was also studied and was found to be higher in patients with higher ABCD2 scores.

Based on these results, the investigators risk-stratified patients based on ABCD2 score. Low risk patients had a score of less than 4, moderate risk patients had a score of 4-5 and high risk patients had a score of 5 or greater. Within the study population, if all patients with moderate or high risk of stroke were hospitalized following a TIA, only 9% of strokes would have occurred outside of the hospital. The authors note that this scoring system should serve as a guide to clinicians, but that the individual characteristics of each patient and the constraints of the health care system will likely dictate whether a patient is hospitalized.

Commentary by Dr. Daniel Labovitz, Director of the NYU Stroke Center:
TIA is a serious diagnosis that demands emergent evaluation and usually requires hospitalization. The study summarized above grew out of a previous study [2] that generated the first empirical scale for assessing risk of cerebral infarct after TIA. The prior study reported a 10.5% risk of stroke within 90 days among 1707 patients diagnosed with TIA by emergency physicians. Strikingly, fully half of those strokes occurred within the first 2 days after the index TIA, yielding a stroke risk similar to that of open-heart surgery. There are two take home messages. First, even though some patients are given the diagnosis of TIA for non-vascular events, the diagnosis carries an extremely high risk of stroke. Second, so much of the risk comes so early that emergent hospitalization for TIA is usually the only practicable way to evaluate and treat possible causes soon enough to make a difference.

1. Johnston SC et. al.Validation and refinement of scores to predict very early stroke risk after transient ischaemic attack.Lancet. 2007 Jan 27;369(9558):283-92. http://sfx.med.nyu.edu/sfxlcl3?genre=article&id=pmid:17258668&_char_set=utf8

2. Johnston SC, et. al. Short-term prognosis after emergency department diagnosis of transient ischemic attack. JAMA 2000;284:2901-2906. http://sfx.med.nyu.edu/sfxlcl3?genre=article&id=pmid:11147987 &_char_set=utf8

Image Courtesy NIH http://lbc.nimh.nih.gov/images/brain.jpg

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