2023 American Academy of Neurology Abstract Website

Objective:

To determine the incidence and prevalence of myasthenia gravis (MG) associated with acetylcholine receptor (AchR)-IgG and muscle tyrosine kinase (MuSK)-IgG in the district of Sassari (Sardinia; Italy).

Background:

The global mean incidence and prevalence of MG have been assessed at ≈15 (range, 4-29)/million and 20 (range, 2-37)/100,000, respectively. The island of Sardinia is a recognized area at higher risk for different immune-mediated disorders (e.g., multiple sclerosis), but the epidemiology of MG remains unclear.

Design/Methods:

From the Neurochemistry Laboratory of the University-Hospital of Sassari (reference laboratory for AchR-IgG/MuSK-IgG testing in the island since 1998) we retrospectively identified patients with: 1) AchR-IgG (titer ≥0.5 nmol/L) and/or MuSK-IgG (titer ≥100 pg/ml) positivity by radioimmunoprecipitation assay; 2) available medical records; and 3) residence within the district of Sassari. Incidence (January 2010-December 2019) and prevalence (on January 1, 2020; population 325,288) were calculated.

Results:

Among 517 antibody-positive patients identified, 183 were included (incident, 97; prevalent, 165). We excluded 334 patients due to: 1) missing clinical information (n=65); 2) residency outside the Sassari district (n=168); 3) not classifiable as incident or prevalent (n=56); and 4) clinical phenotype not consistent with MG (n=45; median AchR-IgG titer, 0.7 [range, 0.5-5.5] nmol/L). The crude MG prevalence was 50.7/100,000 (95% CI, 43.4-58.9), whereas incidence was 29.8/1,000,000 person-years (95% CI, 24.3-36.2). Antibody specificities were AchR in 170 (92.9%; median titer 5.7 [range, 0.5-22]) and MuSK in 13 (7.1%; median titer 1,255 [range, 136-1,730]). Among incidence cases, age at disease onset was distributed as: <18 years (n=2; 2%); 18-50 years (n=14; 14.4%); 51-65 years (n=25; 25.8%); and >65 years (n=56; 57.7%). In 45 (46.4%) incident cases, MG was initially restricted to ocular muscles.

Conclusions:

We report the highest incidence and prevalence of MG worldwide. The environmental and genetic determinants of MG risk in the Sardinian population need to be investigated.