[Clinical symptoms and disability of myotonic dystrophy in Japan]

We performed the first nationwide survey of myotonic dystrophy (MyD) in Japan. This paper reports the result of analysis of clinical pictures and disability of 670 patients found in this survey. 413 cases (61.6%) were males and 257 (38.4%) were females. Male/female ratio was approximately 1.6. The age of onset was most often in the third or fourth decade. Mean age of onset was 27.7 years in the males and 26.8 years in the females. Eight percent of the cases presented their symptoms before the age of 9 years. These cases were considered to belong to congenital or infantile form of MyD. There were also a few patients who started noticing their symptoms after the age of 60 years. Duration of the illness at the time of examination was approximately 13 years in both sexes. Myotonia was observed in 97.3% of the males and 98.1% of the females. Muscular weakness was seen in 99.0% of the males and 96.5% of the females. Atrophy was present in 93.5% of the males and 88.9% of the females. These data showed that almost all cases had these three major symptoms related to the skeletal muscles. There were 16 cases which lacked myotonia, and most of them belonged to congenital or infantile form of MyD. Cataract was present in more than a half of the patients (54.4% in the males and 52.0% in the females). Mental retardation was observed in 42.4% of the males and 35.9% of the females. Frontal baldness was seen much more frequently in the males (74.6%) than in the females (22.7%). Generally, as the duration of the illness was longer, these clinical symptoms were seen in higher frequency.(ABSTRACT TRUNCATED AT 250 WORDS)