Incidence of amyotrophic lateral sclerosis in the local health district of Ferrara, Italy, 1964-1998.

One of the epidemiologic characteristics of amyotrophic lateral sclerosis (ALS) still under discussion is whether the incidence of ALS is increasing over time. We performed a new investigation expanding our previous study of ALS in the local health district (LHD) of Ferrara, northern Italy, to determine whether there have been any changes in the incidence of ALS in the years 1964-1998. We used a complete enumeration approach by reviewing all possible sources of case collection available in the study area. We selected all patients with definite and probable ALS according to the World Federation of Neurology criteria. The mean annual crude incidence rate for 1964-1998 was 1.63 per 100,000 population (95% CI 1.31-2.00). An increase in incidence from 1.07 to 2.19 per 100,000 population was observed during the study period. It was greater in women and in individuals of 70 years old and over. Substantial population ageing occurred in the LHD of Ferrara during the study period and it was more prominent in women. This increase in incidence seems to be explained mainly by the ageing of the population. Moreover, greater precision in diagnosis of ALS in elderly women, rather than better case ascertainment of diagnosed patients, may have contributed to the increase. The role of environmental factors cannot be excluded, but based on the present findings, it seems to be of little importance.