Phenotypic-Genotypic Expansion of Plectinopathy in a Patient With Muscular Dystrophy and Immune-Mediated Myasthenia Gravis

A 26-year-old female with a history of blistering skin lesions, hair loss, and various neurological symptoms was diagnosed with a neuromuscular junction disorder, myasthenia gravis (MG), and muscular dystrophy. The diagnosis was supported by electromyography findings, an acetylcholine receptor antibody test with a titer of 2.36 nmol/L (normal range: ≤ 0.4 nmol/L), and a serum creatine phosphokinase titer of 422 IU/L. The patient's skin lesions were consistent with epidermolysis bullosa. Whole-exome sequencing revealed a novel homozygous nonsense variant in PLEC, suggesting muscle-related plectinopathy. Muscle biopsy and staining showed pathological findings compatible with muscular dystrophy. The patient was treated with a stepwise incremental dose of steroid up to 30 mg/day for 6 weeks, resulting in significant improvement in swallowing, skin lesions, and ptosis. Her MG composite scale decreased from 22 to 12. This case presents novel findings of a combination of muscular dystrophy and immune-based myasthenia gravis in a patient with PLEC mutations.