Temporal trend of amyotrophic lateral sclerosis incidence in southern Europe: a population study in the health district of Ferrara, Italy

Data about the temporal trend of amyotrophic lateral sclerosis (ALS) incidence in southern Europe are scarce. Incidence studies on ALS have been carried out in the health district of Ferrara, Italy, since 1960s. We expanded the previous studies from 1964 to 2009. The study was prospective with a subsequent retrospective intensive survey of multiple sources of case ascertainment. All patients with a definite and probable ALS according to the original El Escorial criteria were selected. There were 130 incident cases in the years 1964-2009 giving an average annual crude incidence of 1.82 per 100,000 population (95% CI 1.53-2.17). An incidence increase during the study period was estimated in women (χ(2) test for trend = 7.19, p < 0.01) and in the elderly (χ(2) test for trend = 7.803, p < 0.01). The age-adjusted incidence was stable over time in both women (1.19 per 100,000, 95% CI 0.90-1.52) and men (1.45 per 100,000, 95% CI 0.12-1.84). The annual number of new ALS cases in the study population followed the Poisson distribution in both sexes as well as in the elderly group of the population. The present findings suggest that ALS incidence is nearly stable over time. The crude incidence increase we estimated over time among women is mainly explained by population ageing. The increasing incidence in the elderly population was likely the consequence of an increasing precision in ALS diagnosis in the elderly since the increasing attention and care over time of neurologic elderly patients that likely concern elderly women more than previous time periods rather than better case ascertainment of diagnosed patients. The present findings do not support the role of specific environmental factors in ALS pathogenesis.