Background The ABCD2 score predicts early risk of stroke in unselected TIA referrals, those with clinically diagnosed TIA and even in those with ‘positive’ DWI. The age, blood pressure (BP) and diabetes elements of the score can all be plausibly related to stroke risk, but it is unclear why motor symptoms indicate high risk.

Methods We studied clinical characteristics of TIA and subsequent stroke in a population-based study. The predictive power of ABCD2 was determined in relation to TOAST subtype and clinical symptoms.

Results Among 1000 patients with TIA, 7-day stroke risk was highest after small vessel disease (SVD) TIAs: 27/109(24.8%) vs 68/891(7.6%), p<0.0001. The ABCD2 score tended to predict 7-day stroke risk best after SVD events (AUC=0.70, 0.58–0.82, p=0.002) and least well after large artery atherosclerosis TIA (0.52, 0.37–0.68, p=0.78). BP≥140/90 was predictive of 7-day stroke risk in all subtypes (81/696, 11.6% vs 14/304, 4.6%,OR=2.7, 1.5–4.9, p<0.001), but motor symptoms owed their predictive value purely to SVD TIAs (23/72, 31.9% vs 46/533, 8.6%, OR=5.0, 2.7–9.3, p<0.001), consistent with capsular warning syndrome. Among all patients with a lacunar TIA, motor symptoms were higher risk than sensory symptoms only (23/72 vs 4/37; OR=3.9, 1.1–14.6, p=0.02), which was, of course, reflected by the ABCD2 score (score ≥4 : 32% vs 10.5%, OR 4.1, 1.3–12.9, p=0.01).

Conclusion The predictive power of motor symptoms in the ABCD2 score is mainly accounted for by hemi-motor lacunar TIAs, reflecting the high stroke risk in capsular warning syndrome.