Epidemiology of seropositive myasthenia gravis in Sardinia: A population‐based study in the district of Sassari

Abstract

Introduction/AimsThe global incidence and prevalence of myasthenia gravis (MG) range between 6–31/million and 10–37/100,000, respectively. Sardinia is a high‐risk region for different immune‐mediated disorders, but the epidemiology of MG remains unclear. We determined the epidemiology of MG with acetylcholine receptor (AChR)‐immunoglobulin G (IgG) and muscle‐specific tyrosine kinase (MuSK)‐IgG in the district of Sassari (North‐Western Sardinia; population, 325,288).MethodsFrom the laboratory of the University Hospital of Sassari (reference for AChR/MuSK‐IgG testing in Sardinia since 1998) and the main neurology units in Sardinia, we retrospectively identified MG patients with (1) AChR‐IgG and/or MuSK‐IgG positivity by radioimmunoprecipitation assay; and (2) residency in the district of Sassari. Incidence (January 2010–December 2019) and prevalence (December 31, 2019) were calculated.ResultsA total of 202 patients were included (incident, 107; prevalent, 180). Antibody specificities were AChR (n = 187 [93%]) and MuSK (n = 15 [7%]). The crude MG incidence (95% confidence interval) was 32.6 (26.8–39.2)/million, while prevalence was 55.3 (47.7–63.9)/100,000. After age‐standardization to the world population, incidence decreased to 18.4 (14.3–22.5)/million, while prevalence decreased to 31.6 (26.1–37.0)/100,000. Among incident cases, age strata (years) at MG onset were: <18 (2%), 18–49 (14%), 50–64 (21%), and ≥65 (63%).DiscussionSardinia is a high‐risk region for MG, with a prevalence that exceeds the European threshold for rare disease. Identification of the environmental and genetic determinants of this risk may improve our understanding of disease pathophysiology.