Treatment of anti-MuSK antibody positive myasthenia gravis

The authors report the case of a 27-year-old woman with muscle-specific receptor tyrosine kinase antibody positive myasthenia with predominantly ocular and bulbar symptoms. Both edrophonium and low dose (4×30 mg/day) pyridostigmin resulted in cholinergic side effects including fasciculation mainly in the facial and neck muscles, and excessive salivation. The patient responded well to a relatively high dose of chronic corticosteroid treatment (methyprednisolone 64mg/day), but the decrease of the corticosteroid dose below 16 mg/day induced exacerbation of the clinical symptoms. Immunosuppression with azathioprine and methotrexate failed to maintain the clinical improvement. However, plasma exchange was always very effective, and all clinical symptoms improved significantly. The authors conclude that patients with muscle-specific receptor tyrosine kinase antibody positive myasthenia gravis should have an individual treatment protocol differing from those used in patients who do not have this antibody but are positive for acetylcholine-receptor antibody. Identification of the pathogenic antibody in the early stage of myasthenia gravis may help to develop the optimal, individualized treatment strategy, to avoid severe side effects, and to achieve fast improvement.