Abstract

INTRODUCTION

Antibodies to the muscle acetylcholine receptor (AChR) are present in about 85% of patients with generalized myasthenia gravis, and 50% of patients with just ocular symptoms. However, up to 70% of the myasthenia patients without AChR antbodies, so called ‘seronegative’ myasthenia gravis, have antibodies to the muscle specific tyrosine kinase (MuSK). MuSK is another protein at the postsynaptic membrane of the neuromuscular junction, and plays a role in agrin-induced AChR clustering (Hoch et al. 2001). These patients may be difficult to recognize, and difficult to treat effectively. Here we describe four AChR antibody-negative/MuSK antibody-positive patients as examples.

THE CASES (SEE TABLE 1)

Case 1

This patient had an age at onset and clinical presentation typical of myasthenia gravis but was difficult to treat. She was a 30-year old woman who developed diplopia, dysphagia and dysarthria during the third trimester of her first pregnancy. EMG showed a defect of neuromuscular