Circadian fluctuations in onset of perimesencephalic hemorrhage

Aneurysmal subarachnoid hemorrhage (aSAH) occurs more often during working hours and in the evening, and thus at times of relatively high blood pressure, with an even distribution over the days of the week in most studies. Perimesencephalic hemorrhage (PMH) is a non-aneurysmal subset of subarachnoid hemorrhage (SAH) without known circadian fluctuation. We studied the time and day of onset in a large series of patients with PMH. For all 249 PMH patients included in our SAH-database we analyzed the time (categorized in 2- and 6-h intervals) and day of onset by calculating rate ratios (RRs) with corresponding 95 % confidence intervals (CIs) for time and day, with the afternoon and Saturday as reference. The risk of PMH was lower between 2–4 AM (RR 0.14; 95 % CI 0.03–0.63), 4–6 AM (RR 0.21; 95 % CI 0.06–0.75) and 6–8 AM (RR 0.07; 95 % CI 0.01–0.54). A tendency towards higher risks in the morning and afternoon was observed. Analyzing the time of onset in 6-h intervals also showed a lower risk (RR 0.35; 95 % CI 0.21–0.58) during night hours (12–6 AM). The risk of PMH was evenly distributed over the days of the week. PMH occurs less often during night hours. The pattern of PMH during the day shows similarities to that seen in aSAH, although the differences over the day are not statistically significant, as they are in aSAH. The occurrence of PMH is evenly distributed over the days of the week, as it is in aSAH.