Isolated dysphagia masking myasthenia gravis diagnosis.

Myasthenia gravis (MG) is an autoimmune disorder of the neuromuscular junction characterized by fluctuating skeletal muscle weakness. We report a 61-year-old woman presenting with progressive dysphagia as the sole initial symptom for 15 months, leading to diagnostic delay. Esophageal manometry suggested ineffective motility, and electroneuromyography was normal, reinforcing a non-neurological hypothesis. During hospitalization for worsening dysphagia, cervical magnetic resonance imaging (MRI) incidentally revealed an anterior mediastinal nodule consistent with thymoma. Pulse corticosteroid therapy caused abrupt clinical deterioration, prompting neurological evaluation. Pyridostigmine produced marked improvement within 48 hours, and acetylcholine receptor antibody testing confirmed MG (18.7 nmol/L, radioimmunoassay). Robotic thymectomy revealed a type AB thymoma. The patient remains stable on azathioprine 2.5 mg/kg/day, with oncologic follow-up. This case highlights that MG should be considered in persistent unexplained dysphagia, particularly when symptoms worsen after corticosteroid exposure. Early recognition avoids morbidity and unnecessary invasive procedures.