Subarachnoid haemorrhage occurrence exhibits a temporal pattern - evidence from meta-analysis

The aim of the present meta-analysis was to determine a temporal pattern of occurrence of subarachnoid haemorrhage (SAH). A MEDLINE 1966-2001 and EMBASE (1980-2001) literature search and hand search of relevant references were performed for population-based incidence studies that reported the time of SAH occurrence. Data from all identified relevant studies were combined into a pooled rate ratio (RR), with corresponding 95% confidence intervals (CI) using the Mantel-Haenszel method. Overall, eight population-based studies were included in the analysis. A total of 2533 first-ever cases of SAH were reported in the studies identified. Risk of SAH occurrence was the highest in the period between 6 am and 12 am (RR=3.19; 95% CI 3.03-3.36; early morning as a reference variable) and between 12 p.m. and 6 p.m. (RR=2.63; 95% CI 2.47-2.80), in winter and spring (RR=1.10; 95% CI: 1.02-1.17; and RR=1.07; 95% CI: 1.01-1.13, respectively; summer as a reference variable) and on Sunday (RR=1.22; 95% CI 1.09-1.37; Monday as a reference variable). The evidence suggests that occurrence of SAH exhibits a seasonal (winter and spring) peak, diurnal (late morning peak) and daily (Sunday peak) pattern. It is suggested that the occurrence of some major acute vascular events (total ischaemic strokes, intracerebral haemorrhage and myocardial infarction) may be influenced by common triggering factors.