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 > or = 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.