Differing temporal patterns of onset in subgroups of patients with intracerebral hemorrhage.

BACKGROUND AND PURPOSE The purpose of this study was to further analyze the temporal patterns of onset of intracerebral hemorrhage (ICH) and to determine whether or not subgroups with specific clinical characteristics exhibit different patterns of onset. METHODS The daily, weekly, and yearly variations in occurrence of ICH together with the relationship between ICH occurrence and changes in air temperature were evaluated in 1018 patients. Patients were grouped according to the presumed etiology of ICH: hypertensive ICH, secondary ICH, and ICH of undetermined origin. The contribution of demographic and clinical factors to the temporal distributions of ICH was also evaluated. RESULTS Marked differences in seasonal and diurnal patterns of ICH onset were observed in the different groups. The incidence of hypertensive ICH reflected seasonal and circadian changes in blood pressure, whereas the latter did not seem related to the onset of nonhypertensive ICH. The seasonal pattern was more evident in elderly patients with hypertensive ICH than in younger subjects. No significant weekly variations were observed; however, risk was greater on Monday in the working population. CONCLUSIONS Our results suggest that the higher incidence of ICH in the colder months is due to the effect of low temperatures on blood pressure and that the clustering of ICH events in the morning is due to the increase in sympathetic tone, and consequent increase in blood pressure, on awakening.