The epidemiology of myasthenia gravis subtypes and the frequency of antibodies to muscle-specific kinase (MuSK) was studied in patients with generalised myasthenia gravis without anti-acetylcholine receptor antibodies who had an onset of symptoms between 1990 and 2004 in a well-defined region in the Netherlands. The nationwide prevalence and incidence of myasthenia gravis with anti-MuSK antibodies were also studied. MuSK antibodies were found in 22% of patients with generalised myasthenia gravis without anti-acetylcholine receptor antibodies. Nationwide, 35 patients with MuSK myasthenia gravis were identified, yielding a prevalence of 1.9 per million (95% confidence interval (CI) 1.22 to 2.59) and an annual incidence 0.10 per million person-years (95% CI 0.06 to 0.14).
- AChR, acetylcholine receptor
- AChR Ab− MG, myasthenia gravis without anti-acetylcholine receptor antibodies
- EMG, electromyography
- MuSK, muscle-specific kinase
- MuSK Ab+ MG, myasthenia gravis with anti-muscle specific kinase antibodies
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Funding: EHN was supported by the Prinses Beatrix Fonds. This project was supported by the Foundation “De Drie Lichten” in The Netherlands.
Competing interests: None.
Published Online First 20 October 2006
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