Background and purpose: MuSK-positive myasthenia gravis (MG) is diagnosed in 0-48% of cases with generalized seronegative MG in different populations. The presence of anti-MuSK antibodies generally relates to a severe course and lack of response to thymectomy. We analyzed for the first time the serology and clinical characteristics of MuSK-positive MG in the Polish population.
Methods: One hundred and fifty-one patients were tested for the presence of anti-AChR and anti-MuSK antibodies: 62 with seronegative MG, including 14 with ocular seronegative MG, 48 age-matched patients with seropositive MG and 41 controls.
Results: All patients with seropositive MG and the disease controls were MuSK-negative. Anti-MuSK antibodies were detected only in four patients with seronegative MG (8.7% of generalized seronegative cases): three women and one man. All four had predominantly bulbar involvement, and underwent thymectomy, with no apparent benefit. All of them improved clinically after immunosuppressive treatment with remissions lasting up to 7 years.
Conclusion: MuSK-positive MG is rare in Polish population accounting for only 8.7% of seronegative cases with generalized MG. This is consistent with emerging evidence for lower MuSK antibodies at more northerly latitudes.