Circadian variation in ischemic stroke subtypes

Background and Purpose-While previous studies suggest that the peak time period for the occurrence of ischemic stroke is in the mid- to late-morning hours, detailed information pertaining to circadian variations among the various stroke subtypes has been limited. The purpose of our study was to define the circadian patterns of symptom onset in an acute stroke trial with an established system for stroke subtype classification. Methods-An analysis was conducted on 1272 patients enrolled in the Trial of Org 10172 in Acute Stroke Treatment (TOAST) study. All patients had a documented time of stroke symptom onset, and all stroke subtype determinations were made by a single rater. Results-The greatest portion of atherothrombotic strokes (25.7%), cardioembolic strokes (30.5%), and strokes of other/unknown mechanism (27.1%) occurred between 6:01 AM and 12:00 noon. The greatest portion of lacunar strokes (31.6%) were present on awakening. More than one half of the infarcts in this series were either present on awakening or occurred in the mid- to late-morning hours. The correlation between stroke subtype and time of symptom onset did not reach statistical significance (P=0.07, Pearson's chi(2) method). Conclusions-Although there is a trend for clustering of ischemic stroke in the morning hours, there is insufficient specificity to predict with any reasonable likelihood the stroke subtype according to the circadian pattern of symptom onset.