Abstract Body: Background: Recent studies have demonstrated time of day variations in ischemic stroke presentation and outcomes with findings that events occurring in the evening hours tend to be more severe, progress faster, and have poorer outcomes. Much less is known about circadian/diurnal influences on intracerebral hemorrhage.

Methods: We analyzed patient records with a final diagnosis of intracerebral hemorrhage (ICH) from the Field Administration of Stroke Therapy - Magnesium (FAST-MAG) randomized trial database. Patients were grouped into six discrete 4-hour time windows by symptom onset time. Patient demographics, clinical features, medical history, stroke severity, and were examined for association with time of day.

Results: Among 380 patients with ICH, 90% had last known well times during the day between 07:00 – 22:59. Thirty-two baseline patient features were generally similar across the six time-of-day intervals, except initial field systolic blood pressure was highest between 19:00 – 22:59 (mean 181 mmHg vs 165 – 176 mmHg) and last known well to paramedic evaluation longest between 03:00 – 10:59 (median 27 min vs 16 – 23 min). Among outcomes, early neurologic deterioration showed diurnal variation, with peaks of 47% between 15:00 – 18:59 and 49% between 19:00 – 22:59 vs 21% – 41% in other intervals (Figure 1). A higher proportion of patients were severely disabled (mRS 5) or dead (mRS 6) at 90 days in the 19:00 – 22:59 (54%) and 23:00 – 02:59 (64%) than in other time intervals.

Conclusions: Hemorrhagic strokes with late afternoon to evening onset times are associated with increased frequency of hyperacute neurological deterioration and poorer 90-day outcomes. This finding suggests that circadian influences upon stroke course have commonalities across ischemic and hemorrhagic stroke subtypes.