A multicenter study of sleep-wake rhythm disorders: clinical features of sleep-wake rhythm disorders.

A multicenter study of sleep-wake rhythm disorders (i.e. non-24 hour sleep-wake syndrome; non-24), delayed sleep phase syndrome (DSPS), irregular sleep-wake pattern (irregular sleepers), and long sleepers, was conducted with the co-operation of 25 institutions. One hundred and twenty-one primary sleep-wake rhythm disorders were diagnosed and were classified as 13 non-24, 90 DSPS, 12 irregular and six long sleepers. The mean onset age was about 20 years old and psycho-social factors associating the onset of the disorder were identified in 36% of these patients. The major factors of sleep-wake disorders were personal relationships, advancing to a higher level education, gaining employment, and changes in environment. Most patients were 'night active' prior to appearance of their symptoms. Increase in night activities of modern society seem to result in the occurrence of such sleep-wake rhythm disorders.