Rizwan Kalani, MD

Vangen-Lønne AM, Wilsgaard T,  Johnsen SH, Carlsson M, and Mathiesen EB. Time Trends in Incidence and Case Fatality of Ischemic Stroke: The Tromsø Study 1977–2010. Stroke. 2015

Though overall stroke incidence and mortality have declined in high-income countries over the past few decades, an increasing incidence in younger populations has been observed. In this study, the authors evaluated the trends in incidence and case fatality of first-ever ischemic stroke in Norway from 1977 to 2010.

Estimated trends came from a population-based, prospective cohort study from Tromso, Norway. First stroke was identified from clinical registries from the University Hospital of North Norway and National Causes of Death Registry. Ischemic stroke was defined per the WHO clinical definition – with no other apparent cause of symptoms demonstrated by brain CT, MRI, or autopsy. Case fatality was determined from the patients who died in the first 30 days after stroke.

Of the 36,575 individuals (over the age of 30 years, without prior stroke) included, there were 1214 incident cases of ischemic stroke. As expected, the incidence rates increased with age and were higher in men. From 1995 to 2010, there was an age- and sex-adjusted 24% decline in incidence; 32% reduction in women and 19% in men. However, for the 30-49 year age group, there was an increasing incidence in women and a (non-significant) rising trend in men. The case fatality for ischemic stroke was 7% for the 30-84 year age group and 20% in those ≥85 years. The age-adjusted case fatality was higher for women compared to men. In older age groups, incidence declined or remained stable (age ≥ 75 years) in both men and women. Over the time period evaluated, though there was a declining case fatality for men 30-84 years, it remained unchanged for women (it actually declined and then increased).

Increasing incidence of ischemic stroke of younger individuals (particularly women) in this population-based study from Norway is consistent with reports from France, Sweden, Netherlands, and the US. This is occurring despite the declining incidence in older individuals in high-income countries. Overall, case fatality declined (in men) or remained stable (in women) in this study. These epidemiologic trends require further investigation to elucidate the causes for increasing stroke in younger age groups and understand the heterogeneity seen between and within different populations. Stroke incidence and associated mortality will need to be followed over time, ideally along with implementation of multifaceted strategies to stroke prevention that targets the high risk groups.