[Update on stroke epidemiology].

In the past 50 years, there have been dramatic changes in the epidemiological profiles of stroke in Japan. Although stroke used to be a leading cause of death between 1950s and 1970s, thereafter stroke mortality rate has declined mainly due to the decrease in the mortality of cerebral hemorrhage and stroke has dropped to the fourth leading cause of death following cancer, heart disease, and pneumonia in 2011. The Akita Stroke Onset Registry (ASOR), which was set up in 1983 to collect data on all stroke events in Akita prefecture, revealed a substantial increase in the incidence of first ever strokes, suggesting a marked increase in the incidence of cerebral infarction, although the age-standardized incidence did not change significantly. These trends were explained by the rapid aging of the population in Akita. Stroke recurrence rates were 22.8%, 17.7%, and 7.0% for cerebral infarction, cerebral hemorrhage, and subarachnoid hemorrhage, respectively. When the index stroke event was cerebral infarction, 84.2% of the recurrence was also cerebral infarction, while 13.6% experienced cerebral hemorrhage. The yearly recurrence rate was highest in the first year following the index stroke event and gradually decreased afterwards. The prevalence of dementia was only 3% in those without a history of stroke events, whereas it was 27% in the stroke survivors in the cohort data. These findings suggest a participation of cerebrovascular lesions in the development and evolution of dementia, especially in the elderly population.