Epidemiology of Amyotrophic Lateral Sclerosis in Western and Northern Finland.

Introduction: The aims of this study were to define the incidence and prevalence of amyotrophic lateral sclerosis (ALS) in two north-western regions in Finland and to assess clinical ALS phenotypes in these areas.

Methods: We conducted a retrospective epidemiologic study by using hospital discharge registers in the regions of Central Ostrobothnia (population 68,158 in 2019) and Northern Ostrobothnia (population 412,830). All patients diagnosed with ALS during 2010-2019 and living in either region were included in the incidence study. The prevalence day was December 31, 2019. All ALS diagnoses were retrospectively re-evaluated and the clinical phenotype data reviewed and reassessed.

Results: In total, 214 ALS patients were identified. The age-adjusted 10-year incidence of ALS was 5.4/100,000 person-years in Central Ostrobothnia and 4.6/100,000 person-years in Northern Ostrobothnia. The age-adjusted prevalence rates were 13.1 and 14.6/100,000, respectively. The mean survival after the diagnosis was 16.8 months. Frontotemporal dementia (FTD) was identified in 15% of all patients. ALS-FTD was relatively more common among patients with bulbar- or respiratory-onset ALS (25%) than among those with limb-onset ALS (8%). Approximately 13% of the ALS patients had a positive family history for ALS. Genetic testing had been performed in 53% of all cases and the most tested mutations were C9orf72 hexanucleotide repeat expansion (32%) and D90A-SOD1 (40%). C9orf72 repeat expansion was detected in 8% and a D90A-SOD1 mutation in 6% of all cases, that is, 26% and 14% of all tested cases, respectively.

Conclusion: The incidence and prevalence rates of ALS in Finland are among the highest in the world. ALS-FTD seems to be more common among patients with bulbar- or respiratory-onset ALS than among those with spinal-onset disease. Cognitive evaluation of ALS patients and offering a possibility to genetic testing should be systematic in clinical practice.