A small subset of patients with myasthenia gravis (about 5%) have antibodies to muscle-specific kinase (anti-MuSK) rather than anti-AChR.
Synonym: anti-muscle-specific tyrosine kinase
Muscle-specific tyrosine kinase forms the core of a protein complex in the postsynaptic membrante at the neuromuscular junction (Reddel et al).
Clinical features tend to be more severe with:
(1) bulbar dysfunction
(2) respiratory muscle weakness with insufficiency
(3) atrophy of facial and tongue muscles
(4) neck muscle weakness
(5) refractory to usual therapy with immunosuppressives
(6) high rate of myasthenic crises
A significant proportion of cases have IgG4 antibodies
Therapy with immunosuppressive agents may be require multiple agents and high doses, resulting in a high rate of adverse effects. Rituximab is promising therapy.
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