Why do acute ischemic stroke patients with a preceding transient ischemic attack present with less severe strokes? Insights from the German Stroke Study.

BACKGROUND: The effect of ischemic preconditioning (IP) is well established in animal models of brain ischemia. There are conflicting data from human observational studies whether IP is also induced by a preceding transient ischemic attack (TIA) resulting in a lower stroke severity in these patients.
METHODS: Data from 7,611 consecutive patients with first-ever acute ischemic stroke from the prospective German Stroke Study Collaboration were analyzed. A multivariate linear regression analysis was used to evaluate whether a preceding TIA was associated with a lower National Institutes of Health Stroke Scale (NIH-SS) score at admission. Furthermore, stroke severity was stratified by the latency between a preceding TIA and subsequent acute ischemic stroke (≤7 days vs. >7 days and ≤72 h vs. >72 h).
RESULTS: A previous TIA was documented in 452 (5.9%) patients, and a significantly lower NIH-SS score at admission was found in these patients compared with patients without TIA. A previous TIA remained significantly associated with a lower NIH-SS score in multivariate analysis corrected for the Trial of Org 10172 in Acute Stroke Treatment (TOAST) classification, cardiovascular risk factors, age, sex and premorbid disability. The NIH-SS score at admission did not significantly differ in 96 patients with a TIA within 7 days compared with 137 patients with a TIA more than 7 days before ischemic stroke. Similarly, there were no significant differences in stroke severity in patients with a TIA within 72 h.
CONCLUSIONS: The significantly lower stroke severity observed in patients with a preceding TIA is not confounded by stroke etiology in our large-scale observational study. Data on latency between the TIA and subsequent ischemic stroke do not support a neuroprotective effect caused by TIA-induced IP in human ischemic stroke.