Objective:To study whether the incidence of subarachnoid hemorrhage (SAH) varies between geographical regions of Finland.Methods:By utilizing the nationwide Causes of Death and Hospital Discharge Registers, we identified all first-ever, hospitalized and sudden-death (dying before hospitalization) SAH events in Finland between 1998 and 2017. Based on the SAH patients’ home residence, we divided SAHs into five geographical regions: 1) Southern, 2) Central, 3) Western, 4) Eastern, and 5) Northern Finland. We calculated crude and European age-standardized (ESP2013) SAH incidence rates for each region, and used a Poisson regression model to calculate age-, sex- and calendar year-adjusted incidence rate ratios (IRRs) and 95% confidence intervals for regional and time-dependent differences.Results:During the total 106 510 337 cumulative person-years, we identified 9 443 first-ever SAH cases, of which 24% died before hospitalization. As compared to Western Finland, where the SAH incidence was the lowest (7.4 per 100 000 persons), the ESP-standardized SAH incidence was 1.4 times higher in Eastern (10.2 per 100 000 persons; adjusted IRR=1.37 (1.27–1.47)) and Northern Finland (10.4 per 100 000 persons; adjusted IRR=1.40 (1.30–1.51)). These differences were similar when men and women were analyzed independently. Although SAH incidence rates decreased in all five regions over two decades, the rate of decrease varied significantly by region.Conclusion:SAH incidence appears to vary substantially by region in Finland. Our results suggest that regional SAH studies can identify high-risk subpopulations, but can also considerably over- or underestimate incidence on a nationwide level.

As the number of obese people is globally increasing, reports about the putative protective effect of obesity in life-threatening diseases, such as subarachnoid hemorrhage (SAH), are gaining more interest. This theory-the obesity paradox-is challenging to study, and the impact of obesity has remained unclear in survival of several critical illnesses, including SAH. Thus, we performed a systematic review to clarify the relation of obesity and SAH mortality. Our study protocol included systematic literature search in PubMed, Scopus, and Cochrane library databases, whereas risk-of-bias estimation and quality of each selected study were evaluated by the Critical Appraisal Skills Program and Cochrane Collaboration guidelines. A directional power analysis was performed to estimate sufficient sample size for significant results. From 176 reviewed studies, six fulfilled our eligibility criteria for qualitative analysis. One study found paradoxical effect (odds ratio, OR = 0.83 (0.74-0.92)) between morbid obesity (body mass index (BMI) > 40) and in-hospital SAH mortality, and another study found the effect between continuously increasing BMI and both short-term (OR = 0.90 (0.82-0.99)) and long-term SAH mortalities (OR = 0.92 (0.85-0.98)). However, according to our quality assessment, methodological shortcomings expose all reviewed studies to a high-risk-of-bias. Even though two studies suggest that obesity may protect SAH patients from death in the acute phase, all reviewed studies suffered from methodological shortcomings that have been typical in the research field of obesity paradox. Therefore, no definite conclusions could be drawn.