[Ocular involvement in MuSK antibody-positive myasthenia gravis]

Antibodies (Ab) against the acetylcholine receptor (AChR) are found in 80 - 90 % of generalized myasthenia gravis (MG), but only in 50 % of pure ocular MG. Furthermore, Ab against the muscle-specific receptor tyrosine kinase (MuSK) were detected in 38 - 54 % of patients with AChR-Ab-negative ("seronegative") MG, but not in pure ocular MG.

2 case reports have been analysed: two patients (42 years old and 61 years old) with primary ocular MG were studied. Both patients complained of fluctuating bilateral ptosis and double vision lasting for 2 to 3 months.

AChR-Ab were negative but MuSK-Ab were clearly positive. In spite of treatment with pyridostigmine and prednisolone, the symptoms in patient 1 generalized within 4 weeks causing dysphagia, limb muscle weakness and respiratory crisis. Symptoms immediately responded to plasmapheresis. Patient 2 clearly improved under treatment with pyridostigmine, methylprednisone, and azathioprine. There was no generalization within a course of 12 months.

Both cases clearly indicate that MuSK-Ab can be found in primary isolated ocular MG lasting for 2 to 3 months. In a primary ocular manifestation of MG the detection of MuSK might indicate the risk for subsequent generalization and might have implications for immunosuppressive therapy. Therefore, seronegative MG requires testing for MuSK-Ab.