Introduction: Aneurysmal subarachnoid hemorrhage (aSAH) is a potentially life threatening neurosurgical emergency. It has been previously believed and taught that subarachnoid hemorrhage has a seasonal variation, with a higher incidence in winter months. Several institutional studies have also demonstrated this to be true1. However, recent analysis of the healthcare utilization project (HCUP) national inpatient sample (NIS) did not demonstrate any variation with seasons2. Other work has utilized the HCUP database to determine aSAH severity and outcomes of aSAH at initial presentation3, and created a metric called the Subarachnoid Stroke Severity Scale (SAH-SSS). Our investigation is the first to the authors' knowledge to study how the severity of subarachnoid hemorrhage varies with the season.
Methods: The HCUP database was queried in New York, Iowa, California, and Washington in order to capture a broad base of the American population. Patients were selected if they had an aSAH as their primary admitting diagnosis. The SAH-SSS was calculated using the prior work from Washington et al. Statistical analysis was conducted in Python 2.7 and R 3.3.0, using Pandas and Matplotlib to process, subset, and visualize the data.
Results: The SAH-SSS was calculated for the four states for each season. The average score was 2.9 in the fall, 2.96 in the spring, 2.97 in the summer, and 3.01 in the winter. A one-way ANOVA did not reveal any statistical difference in mean scores (p=0.04). The incidence of scores also did not vary significantly across the season. In state by state analysis, there was also no variance by season.
Conclusions: While the debate regarding the seasonal incidence of aSAH may remain unresolved, there appears to be no seasonal variation in the clinical severity based on national inpatient registry data.
Patient Care: Allow clinicians to recognize their bias when treating aneurysmal subarachnoid hemorrhage
Learning Objectives: Seasonal variation of aneurysmal subarachnoid hemorrhage
References: 1.Inagawa T. Seasonal variation in the incidence of aneurysmal subarachnoid hemorrhage in hospital- and community-based studies. J Neurosurg. Mar 2002;96(3):497-509.
2.McDonald RJ, McDonald JS, Bida JP, Kallmes DF, Cloft HJ. Subarachnoid hemorrhage incidence in the United States does not vary with season or temperature. AJNR Am J Neuroradiol. Oct 2012;33(9):1663-1668.
3.Washington CW, Derdeyn CP, Dacey RG, Jr., Dhar R, Zipfel GJ. Analysis of subarachnoid hemorrhage using the Nationwide Inpatient Sample: the NIS-SAH Severity Score and Outcome Measure. J Neurosurg. Aug 2014;121(2):482-489.