Thymoma Type B2 Associated with Myasthenia Gravis Presenting as Progressive Respiratory Distress: A Case Report

The association between thymoma and myasthenia gravis (MG) is well established; therefore, the significance of this case does not rest on the coexistence of these conditions alone. Its educational value lies in the diagnostic pathway, in which fluctuating myasthenic symptoms preceded tumor recognition, the initial chest radiograph did not demonstrate an evident mediastinal mass, and contrast-enhanced computed tomography (CECT) subsequently identified a necrotic anterior mediastinal lesion. A 54-year-old woman presented with progressive dyspnea, generalized fatigable weakness, dysphagia, facial muscle cramps, and bilateral eyelid heaviness. Her symptoms worsened with physical activity and improved with rest and pyridostigmine therapy, supporting a clinical diagnosis of MG. Preoperative acetylcholine receptor antibody testing, muscle-specific kinase antibody testing, repetitive nerve stimulation, and baseline electromyography were not documented in the available case records. Chest radiography demonstrated cardiomegaly with aortic dilatation and elongation, but no definite mediastinal mass. Thoracic CECT revealed a well-circumscribed, non-calcified anterior mediastinal isodense lesion with post-contrast enhancement and central necrosis, measuring approximately 3.34 × 2.03 × 2.99 cm. Bronchoscopy was performed as an adjunctive respiratory workup and showed hyperemic and cicatricial mucosa with mucopurulent secretions; cytology showed no malignant cells, and aerobic culture showed no growth. The patient underwent wide excision of a left superior anterior mediastinal mass through an anterolateral thoracotomy approach. Histopathology confirmed WHO type B2 thymoma with invasion into connective and adipose tissue, most consistent with Masaoka-Koga stage II. The patient had favorable early postoperative neurological improvement, and postoperative electromyography showed no persistent neuromuscular transmission abnormality. This case suggests that clinically typical MG may provide an early diagnostic clue to occult thymoma even when chest radiography is unrevealing. Because this is a single case report and long-term follow-up data were not available in the source documentation, the durability of neurological remission and oncological control should be interpreted cautiously and assessed through continued surveillance.