Background: In the early 2000s, three studies were combined to develop the ABCD2 decision rule for predicting the short-term risk of stroke following a TIA (Age, Blood pressure, Clinical features, Duration of symptoms and Diabetes). These were retrospective studies using registry data. The current paper was actually the first to attempt to externally validate this rule prospectively and remains the largest ED-based study to date.
Perry JJ, Sharma M, Sivilotti MLA, et al. Prospective validation of the ABCD2 score for patients in the emergency department with transient ischemic attack. CMAJ. 2011;183(10):1137-45.
The paper: A prospective multi-centre cohort study involving 2,056 patients with a diagnosis of TIA. Each had an ABCD2 score calculated and each was followed up at 7 and 90 days to determine whether they had had a stroke or any further episodes of TIA. The final diagnosis had to be confirmed by at least two independent neurologists. An ABCD2 score of 0 or 1 was found to be 100% sensitive, but few patients fell into this category. Taking the usual UK cut-off, a score of 3 was 92% sensitive and 33% specific for predicting stroke, while a score of 4 was 66% sensitive and 57% specific (these numbers did not change significantly from 7 to 90 days). They also found that the score was calculated incorrectly in the ED in 33% of cases. The commonest error was not scoring unilateral weakness if this was mentioned in the history but was no longer present on examination.
The bottom line: The ABCD2 score is inaccurate as a predictor of imminent stroke. The cut-off of 4 was not particularly sensitive or specific in this large prospective study.
Notes: It seems as though national guidelines are slowly being updated as a result of this study (and others)...
"Patients with suspected TIA should have a full diagnostic assessment urgently without further risk stratification." (Royal College of Physicians (2016)
"If a person has had a suspected TIA within the last week, give aspirin 300mg immediately and arrange urgent assessment (within 24 hours) by a specialist stroke physician... Discuss the need for admission if the person has had more than one suspected TIA or they may be unable to attend." (NICE Clinical Knowledge Summary, updated 2017)
Risk stratification should be based on clinical features only... High-risk symptoms are unilateral motor weakness or speech disturbance; moderate-risk symptoms are unilateral sensory changes, painless visual loss, diplopia or ataxia (paraphrased from the Canadian Association of Emergency Physicians Stroke Best Practice Recommendations 2018)