Differential features of motor neuron disease mortality in Spain

Background. The objective of this study was to describe the temporal and spatial patterns of motor neuron disease (MND) in Spain. Methods. We studied data where MND was stated as the principal cause of death in official statistics from Spain. Time trends were analysed for age-, sex-specific and age-adjusted rates for the period 1951-1990. Age-adjusted mortality and relative risk, obtained by Poisson regression adjusting for age, were calculated for each province from deaths during the period 1975-1988. Maps were constructed using log transformed rates. Statistical significance of spatial aggregation was assessed using the Ohno et al. test. Results. The 1951-1990 mortality rate, age-and sex-adjusted to the European population, for the population aged greater than or equal to 40 years was 1.49 per 100 000; 1.90 and 1.21 for males and females respectively, In general, mortality increased with age. Age-adjusted rates rose until 1960, dropped by 70% during the 1960s and declined slightly over the 1951-1990 period as a whole. From 1970 onwards MND mortality rose evenly, particularly in the 60-69 age group. A North-South gradient was suggested for both sexes with statistically significant clustering in the Northern coastal regions and-for males alone-in the Midwest provinces. Conclusions. Mortality from MND in Spain displayed a magnitude and recently rising temporal trend similar to that described in several other countries. Specific traits were: a decrease during the 1960s, which has been described for Japan only, as well as spatial heterogeneity and a predominant recent increase among the 60-69 age group. The determinants of these unusual MND mortality patterns are unknown.