Treatment of Thymoma-Associated Myasthenia Gravis With Stereotactic Body Radiotherapy: A Case Report

Background: Definitive treatment of thymoma includes surgical resection. The usual approach for thymoma with myasthenia gravis involves treating myasthenia gravis first followed by thymectomy.

Objective: To describe an alternative approach for treating thymoma-associated myasthenia gravis.

Case Report: A 67-year-old man presented to the emergency department with hypercarbic respiratory failure, had respiratory arrest, was intubated emergently, and then was admitted to the medical intensive care unit. He had a 6-month history of unintentional weight loss, progressive fatigue, upper and lower limb fasciculations, bilateral ptosis, dysphagia, dysphonia, and hypopnea. Chest computed tomography (CT) showed a well-circumscribed, 38 × 20–mm anterior mediastinal mass, which was mildly fluorodeoxyglucose-avid on positron emission tomography (PET)–CT. Imaging characteristics and presenting symptoms favored thymoma, although other possibilities were considered. Neurologic evaluation was remarkable for mild confusion, difficulty following multistep commands, prominent fasciculations in all limbs, and diffuse moderate limb muscle weakness without fatigability. Sensation and tendon reflexes were preserved. Cranial nerves were normal except for mild eyelid closure weakness. Routine nerve conduction studies were normal. Repetitive left spinal accessory nerve stimulations at 3 Hz showed a decremental response from the trapezius muscle, suggestive of a neuromuscular junction disorder. Needle electromyography showed widespread myotonic discharges without myopathic change. Acetylcholine receptor binding antibodies were markedly elevated (48.53 nmol/L). These findings supported a diagnosis of myasthenia gravis.