Introduction: The incidence of Amyotrophic lateral sclerosis (ALS) worldwide is approximately 1-2.6/1,000,000 and prevalence 5-6/100,000. ALS has been suggested to be relatively common in Finland but epidemiological information on the subject is scarce and outdated. Material and methods: Patients with ALS diagnostic codes were identified from mandatory administrative registries in the provinces of Southwestern Finland (population circa 430,000) and North Karelia (population circa 170,000) together comprising 11.7 % of the total population of Finland. The diagnoses were verified, and data extracted by reviewing the patient records. Incidence period was 2010-2018, and the prevalence date December 31, 2018. Age-standardization was performed using European Standard Population 2013 (ESP2013) Results: Overall crude incidence of ALS was 4.2/100'000 person-years in Southwestern Finland (ESP2013: 4.0/100,000) and 5.6/100,000 person-years in North Karelia (ESP2013: 4.8/100,000), while crude prevalences were 11,9/100,000 (ESP2013: 10.5/100,000) and 10,9/100'000 (ESP2013: 9.3/100,000), respectively. Mean age at diagnosis was 65.5-71.6 years in women (higher in Southwestern Finland compared to North Karelia, p=0.003) and 64.7-67.3 years in men (no difference between provinces, p=0.39). The diagnosis had been made in 50 % before the age of 70 years in Southwestern Finland and before the age of 65 years in 51 % in North Karelia. Genetic testing had been conducted in 28 % of all patients with the most common findings being SOD1 and c9orf72. After the diagnosis, mean survival was 2.0-2.7 and median survival 1.3-1.4 years. Onset phenotype (p<0.001), age at diagnosis (p<0.001) and genotype (p=0.001) predicted survival. Riluzole had been used by 25 % of patients and tracheostomy and invasive ventilation (TIV) had been performed in <1 %. Conclusions: Both incidence and prevalence of ALS in Finland are among the highest in the world but with some notable differences between the eastern and southwestern parts of the country. Low median life expectancy may be related to the advanced age of patients and the high prevalence of c9orf72 repeat expansion in Finland as well infrequent use of TIV and Riluzole.

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