Incidence of motor neuron disease/amyotrophic lateral sclerosis in South Africa: a 4-year prospective study

Background and purpose: Little is known about the epidemiological features of amyotrophic lateral sclerosis (ALS) in sub-Saharan Africa, and data from the region are limited to clinical series or case reports. The aim of the study was to investigate the incidence rate and presentation of ALS in an ethnically diverse region of South Africa. Methods: We performed a 4-year prospective incidence study in the Western Cape Province of South Africa between 1 July 2014 and 30 June 2018, and used a two-source capture-recapture method for case ascertainment. Age- and sex-adjusted incidence rates (ASAIRs) were calculated using the 2010 US population as the reference. Results: A total of 203 incident cases were identified over the study period, resulting in a crude incidence rate (IR) of 1.09 [95% confidence interval (CI) 0.94–1.24] per 100 000 person-years in the at-risk population (aged >15 years). Capture-recapture analysis resulted in an estimated IR of 1.11 (95% CI 1.01–1.22) per 100 000 person-years. The ASAIR was 1.67 (95% CI 1.09–2.26) overall; 1.99 (95% CI 1.60–2.39) for men and 1.37 (95% CI 1.06–1.68) for women. When analysed separately, there was a substantial difference in ASAIRs between the different population groups, with the highest in the European ancestry group (2.62; 95% CI 2.49–2.75), the lowest in the African ancestry group (0.56, 95% CI 0.0–1.23), and an ASAIR in between these two in the mixed ancestry group (1.09, 95% CI 0.80–1.37). Conclusion: The overall incidence of ALS in the Western Cape Province of South Africa appears to be lower than in North African and Western countries, but higher than in Asian countries. As suggested by previous epidemiological studies, ALS may be less frequent in people of African ancestry.