Epidemiologic Trends of Amyotrophic Lateral Sclerosis in Ireland, 1996-2021

The objective of this study was to examine changes to the incidence, prevalence, age at onset, and survival of patients diagnosed with amyotrophic lateral sclerosis (ALS) in the Republic of Ireland over 25 years.

Incident and prevalent cases of ALS were estimated using the Irish population-based ALS Register, which has been in continuous operation since 1994. Incident cases were age standardized using the direct method and applied to 3 standard populations (Irish, European, and American). Survival was determined using Kaplan-Meier curves and Cox regression models. Non-normally distributed groups were compared using the Kruskal-Wallis test with a Bonferroni correction.

A total of 2,771 patients with ALS were identified in the Republic of Ireland over 25 years. Incidence per 100,000 was determined for the population older than 15 years. Crude incidence increased from 2.64 to 5.46 per 100,000. Standardized incidence increased from 2.64 to 3.1 per 100,000. Prevalence increased from 5.83 to 8.10 per 100,000. The median age at onset increased from 64 to 67 years. The peak age of incidence increased from those between 70 and 74 years to those between 75 and 79 years. Overall, women had a consistently later median age at onset of 67 years compared with men at 65 years (p < 0.001). No significant difference in survival was noted between those captured across 3 different epochs (1996-2003, 2004-2012, 2013-2021). Older age at onset (hazard ratio [HR] 1.03, CI 1.02-1.04, p < 0.001) was a negative predictive factor of survival in multivariate Cox regression analysis. Riluzole use (HR 0.67, CI 0.50-0.90, p = 0.033) and diagnostic delay (HR 0.98, CI 0.98-0.99, p < 0.001) were positive predictive factors.

Within the Republic of Ireland, the age-standardized overall incidence, peak incidence, prevalence, and age at onset of ALS have all increased over 25 years. Despite the widespread use of noninvasive ventilation, aggressive secretion management, and changes in ALS care, the mean survival within the Irish population has not changed.