EPIDEMIOLOGY OF MOTOR-NEURON DISEASE IN THE KII PENINSULA OF JAPAN, 1989-1993 - ACTIVE OR DISAPPEARING FOCUS

During the period 1989-1993, the incidence and migration patterns of p atients with motor neuron diseases (MND) in Wakayama Prefecture, inclu ding one of the high-incidence Kii Peninsula foci ('Kozagawa focus'), were surveyed to determine whether the focus had truly disappeared or not. Overall, the crude average annual incidence was 1.43 per 100 000 population; when age-adjusted to the 1990 Japanese population, it was 1.25 (1.85 for males and 0.61 for females). The average annual age-and sex-specific incidence steadily increased to a peak between 60 and 69 years and dropped after 70. Geographically, the rates varied in the f ive regions of Wakayama Prefecture from 0.38 to 2.48. The areas with h igh incidence were distributed in the central and southernmost regions ; the highest was in the Kozagawa focus with 9.54 (two ALS cases withi n five years; 4193 base population, 1990). During the study period, fo ur emigrants from Kozagawa had developed MND one to four decades after leaving the focus. Although the remarkable clustering of MND was thou ght to have disappeared, the southern Kii Peninsula remains a high-ris k area for MND, especially if one interprets the data so as to include the emigrants. In general, the age at onset has increased in the past 20 years from 56.5 to 61.7; male predominance is observed. (C) 1998 E lsevier Science B.V.