Decline and rise of mortality from motor neuron disease in Spain, 1960-1989: demographic, environmental and competitive influences.

Abstract

Mortality rates from motor neuron disease (MND) in Spain were analysed for the years 1960-1989, a period in which 3,530 deaths were recorded from the disease and during which the crude annual mortality rate ranged between 0.35 and 0.95 deaths per 100,000 persons. Whilst the crude mortality rate fell by 54% during the decade 1960-1969, there was a net increase of 26% over the entire period. The influence of three sets of variables-the increasing mean age of the population, changing environmental factors, and changing competition between diseases-upon mortality rates were investigated through Gompertzian analysis of crude and age-adjusted mortality rates. The increased mean age of the population contributed significantly to the overall rise in mortality from MND over the whole period, a feature that has previously been demonstrated to occur in the majority of industrialised countries. The unusual pattern of a decline and subsequent rise in mortality appears to be due to the influence of changing environmental factors on a sub-population susceptible to the disease.