Giant cell myositis associated with concurrent myasthenia gravis: a case-based review of the literature

The term "giant cell myositis" has been used to refer to muscle diseases characterized histologically by multinucleated giant cells. Myasthenia gravis is an autoimmune neuromuscular junction disorder. The rare concurrence of giant cell myositis with myasthenia gravis has been reported; however, the clinical and histological features have varied widely. Here, we present such a case and a review of the literature. An 82-year-old woman admitted for subacute, progressive, proximal muscle weakness developed acute-onset dysphagia, dysphonia, and respiratory distress 5 days after admission. Laboratory findings were positive for acetylcholine receptor binding antibodies and striational muscle antibodies against titin. Muscle biopsy demonstrated widespread muscle fiber necrosis with multinucleated giant cells, consistent with giant cell myositis. She died despite treatment with pulse methylprednisolone and plasma exchange. A literature review of the PubMed and Scopus databases from 1944 to 2020 identified 15 additional cases of these co-existing diagnoses. We found that giant cell myositis with myasthenia gravis primarily affects female patients, is typically diagnosed in the 6-7th decades, and is characterized by the presence of thymoma. Muscle histology predominantly shows giant cell infiltrate without granulomas. The onset of myasthenia gravis symptoms may precede, follow, or coincide with symptoms of myositis. Treatment with thymectomy, anticholinesterase inhibitors, or immunosuppressive therapy may lead to favorable clinical outcomes.