Abstract
Background Myasthenia Gravis (MG) is an autoimmune condition due to Acetyl Choline Receptor (AChR) antibodies and characterized by ocular or skeletal muscle weakness. Approximately 10–15% of patient with MG have thymoma and 20–25% of the patients with thymoma have MG. Patients with non MG thymoma rarely develop MG symptoms and called postoperative MG (PMG). We report a case of late onset MG in patient treated for malignant thymoma.
Method A 38 years old female present with generalized fatigability, tiredness, dropping of the eyelid, chewing and swallowing difficulty in June 2021. Her AchR antibody was positive.
She was diagnosed to have stage 4 thymic carcinoma in 2013 which was initially treated with radiation and chemotherapy followed by thymectomy with right lung pneumonectomy and right hemidiaphragm resection. She is in remission on follow up PET scan.
Her myasthenic symptoms are well controlled with Mestinon, Methotrexate and IV Immunoglobulin.
She has pleural recurrence of the thymic tumour in June 2023.
Discussion The incidence of PMG in patients with thymoma without MG is very low, ranging from 0.9 to 28%. The interval between thymectomy and onset of MG symptoms varies form immediately post operatively to 326 months and divided into early onset (<6 months) to late onset (>6 months). Preoperative seropositive AChR Ab, open thymectomy, , post-operative lung infection, WHO Type B tumor and non R0 resection are risk factors for development of PMG.
Our patient developed MG symptoms almost after 9 years of thymectomy even though she had preoperative negative AChR Ab.
