Seasonal variation of non-embolic cerebral infarction

Abstract

IT IS well accepted today that the prevalence of diseases caused by microorganisms is altered by climatic fluctuations. The increased incidence of pulmonary infection [l] in the winter and of poliomyelitis and gastro-intestinal infections in the summer are the best examples of this and probably reflect a combination of variations in (1) the host’s susceptibilities; (2) bacterial or viral virulence; and (3) vector availability. Stroke should not have a seasonal variation unless the major causative factors underlying its precipitation, including for instance atherosclerosis and circulatory dynamics, are modified by climate and season. Such factors as eating and drinking habits vary with the temperature; summer dehydration may alter circulatory dynamics and lead to cerebral infarction. There are suggestions of a seasonal variation in cholesterol levels in a stable population of men aged 46-62. Cholesterol levels were found to be highest from November to March and lowest during the summer months, May through August [2, 31. In a similar study involving both sexes, males and females showed seasonal variations of cholesterol levels in opposite directions [4]. Protein bound iodine levels have been found to vary seasonally, the lowest values found during June, July and August with high values in September, October, February and March [4]. The gap between these suggestions of seasonal variation in serum cholesterol and PBI and the occurrence of stroke is too wide for any meaningful connection. Some evidence for a seasonal variation in atherosclerotic disease is found in studies of coronary heart disease. Death from cardiovascular disease in some parts of the United States has a peak during December to April with a low point in August and September [6, 71. The reduction of death rates during the summer months has been confirmed in studies in areas with a marked seasonal climatic variation but not in areas which are continuously warm [S]. In Australia cardiovascular deaths are higher during their winter months, June through September, and lowest during their summer months, January through April [9]. In the field of cerebrovascular disease Takakashi in Japan found that cerebral hemorrhage had a low incidence in the summer months, June to September, and a high incidence in the winter months [IO].