Circadian variation in ischemic stroke subtypes

Background and Purpose-While previous studies suggest that the peak time pe riod for the occurrence of ischemic stroke is in the mid- to late-morning h ours, detailed information pertaining to circadian variations among the var ious stroke subtypes has been limited. The purpose of our study was to defi ne 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 docu mented 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%), cardioemb olic strokes (30.5%), and strokes of other/unknown mechanism (27.1%) occurr ed 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 th is series were either present on awakening or occurred in the mid- to late- morning hours. The correlation between stroke subtype and time of symptom o nset did not reach statistical significance (P=0.07, Pearson's chi(2) metho d). Conclusions-Although there is a trend for clustering of ischemic stroke in the morning hours, there is insufficient specificity to predict with any re asonable likelihood the stroke subtype according to the circadian pattern o f symptom onset.