Demographic, circadian, and climatic factors in non-aneurysmal versus aneursymal subarachnoid hemorrhage

Background: Although, the relationship of spontaneous subarachnoid hemorrhage (SAH) to climatic or circadian factors has been widely studied, epidemiologic, circardian and climatic factors in non-aneurysmal SAH (naSAH), particularly perimesencephalic SAH (PMH), has not been reported before. Objective: For the first time, demographic, climatic, and circadian variables are examined together as possible contributing factors comparing aSAH and naSAH. Methods: We reviewed records for 384 patients admitted to University of Wisconsin Neurosurgery Service from January 2005 to December 2010 with spontaneous non-traumatic SAH. Patients were grouped as aSAH (n = 338) or naSAH (n = 46) on clinical and radiological criteria. PMH (n = 32) was identified as a subgroup of naSAH based on radiological criteria. We logged demographic data, time of SAH, temperature at onset and atmospheric pressure at onset. The three subgroups were compared. Results: Aneurysmal SAH occurred most often from 6 am to 12 pm (p < 0.001); this correlation was not found in naSAH or PMH subgroups. Demographic analysis demonstrated predominance of female gender (p = 0.008) and smoking (p = 0.002) in aSAH, with predominance of hypercholesterolemia in naSAH (p = 0.033). Atmospheric pressure, correlated with aSAH in the main county referral area, where we had detailed weather data (p < 0.05); however, there was no weather correlation in the entire referral region taken together. Multivariate analysis supported a statistical difference only in smoking status between aSAH and naSAH groups (p = 0.0159). Conclusion: Statistical differences in gender, smoking status, and history of hypercholesterolemia support a clinical distinction between aSAH and naSAH. Furthermore, circadian patterning of aSAH is not reproduced in naSAH, supporting pathophysiologic differences. Only smoking status provides a robust difference in aSAH and naSAH groups. Our data prompt further investigation into the relationship between aSAH and atmospheric pressure. (C) 2012 Elsevier B.V. All rights reserved.