A 40-year-old woman presents with bilateral ptosis worse in the evening, diplopia, and fatigable proximal weakness. Edrophonium (Tensilon) test is positive. Anti-AChR antibodies are positive. CT chest shows a 4 cm anterior mediastinal mass. The most appropriate next step after diagnosis is confirmed is:

• A Start high-dose pyridostigmine alone and monitor
• B Radiotherapy to the mediastinum without surgery
• C Thymectomy for thymoma-associated myasthenia gravis ✓
• D Start rituximab as first-line immunotherapy

Explanation

The presence of a thymoma (anterior mediastinal mass) in myasthenia gravis is an absolute indication for thymectomy, as thymomas carry malignant potential regardless of MG symptoms. Perioperative preparation with acetylcholinesterase inhibitors and immunosuppression is required. The MGTX trial confirmed that thymectomy improves outcomes even in non-thymomatous MG. Pyridostigmine alone provides symptomatic relief but does not address the thymoma.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

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Written and medically reviewed by the StethoPrep medical team.