Geographical clustering of amyotrophic lateral sclerosis in South-East England: a population study

BACKGROUND Amyotrophic lateral sclerosis (ALS) is a degenerative disease of motor neurons that causes progressive paralysis and eventually results in death from respiratory failure. Environmental factors that trigger ALS might result in a pattern of geographical clustering of cases. We tested this hypothesis using the South-East England ALS population register, which covers south-east London, Kent and parts of neighbouring counties. METHODS The register's catchment area was divided into postcode districts and sectors. The expected rates of ALS (adjusted for age and sex) were compared with the observed rates using a standardised residuals method and the SaTScan programme. RESULTS There were 406 cases of ALS identified in the catchment area during the study period. Four of the 126 postcode districts, all in Greater London, had residuals >2.5 SDs from the mean. Similarly, there were 15 postcode sectors (out of 420) that had residuals >1.96 SDs from the mean. Nine of these were in Greater London. SaTScan identified an area that had a 5.61-km radius in which the relative risk of ALS was 1.70 (p = 0.012). This area overlapped with the postcode districts and some of the sectors identified using the residuals method. CONCLUSIONS These findings suggest an excess of ALS cases in some postcode districts in south-east England