Increasing incidence of ALS in Canterbury, New Zealand

Abstract

We performed a prospective study of amyotrophic lateral sclerosis (ALS) in North Canterbury, New Zealand, from 1985 to 2006, to ascertain the incidence of ALS over that 22-year period, and to detect patterns of change in incidence. We also aimed to identify factors that influenced survival. A prospective database of all patients seen at the Department of Neurology at Christchurch Public Hospital formed the basis of this study. Additional cases were identified through hospital coding data and from neurologists' private practice records. Kaplan-Meier life table analysis and Cox proportional hazards analyses were used for the survival analysis. Poisson regression and capture-recapture techniques were used to analyze incidence data. ALS incidence rates steadily increased by 3% per year over the 22 years, from 1.6 to 3.3 per 100,000 per year. Older age, bulbar symptoms, and male sex adversely affected survival. The median survival from diagnosis was 17.6 months and from symptom onset 27.6 months. Contemporary supportive therapies such as noninvasive ventilation and percutaneous endoscopic gastrostomy did not extend survival. There was no disease clustering and no clues to etiology were revealed. We report the highest recorded incidence of amyotrophic lateral sclerosis (ALS) to date, with the incidence of ALS in Canterbury increasing over the 22 years of the study. We were unable to confirm improvement in survival using contemporary supportive therapies and confirmed older age, male sex, and bulbar onset as adverse prognostic factors. The increasing incidence is not explained by aging of the population.