Mixed connective tissue disease presenting myasthenia gravis.

We herein describe a 41-year-old female patient with an association of myasthenia gravis (MG) with anti-acetylcholine receptor (AcR) antibody, mixed connective tissue disease (MCTD) and Sjögren's syndrome (SjS). We reviewed the reported association of MG and MCTD, systemic lupus erythematosus, progressive systemic sclerosis, polymyositis and dermatomyositis, and SjS. Since we could find only two patients who fulfilled the diagnostic criteria for MCTD in the previous literature, we concluded that the association of MG and MCTD is rare. We also discuss the coexistence of SjS as one of the underlying pathological conditions for the association of MG and various connective tissue diseases including MCTD.