Positional Respiratory Distress in Myasthenic Crisis: A Case of Undiagnosed Thymoma

Myasthenia gravis (MG) is a chronic autoimmune neuromuscular disorder that can present with life-threatening complications, including myasthenic crisis (MC). We present the case of a 52-year-old Hispanic male with known MG who presented to a hospital serving an underserved community with respiratory distress after discontinuing azathioprine. He was initially presumed to be experiencing a typical MC but then exhibited positional respiratory compromise, an inability to tolerate the supine position and the inability to have a nasogastric tube placed, which raised concern for dynamic extrinsic compression of mediastinal structures. These atypical findings prompted imaging, which revealed a large anterior mediastinal mass consistent with thymoma. The patient's respiratory status worsened when supine, suggesting posture-dependent mass effect likely exacerbated by gravitational forces and impaired diaphragmatic mechanics. The tumor was found to be abutting both phrenic nerves, contributing to diaphragmatic dysfunction and worsening bulbar symptoms. He underwent successful surgical resection but required prolonged postoperative support, including tracheostomy and gastrostomy tube placement. This case highlights the need for heightened clinical suspicion of thymoma in MG patients presenting with crisis, particularly when positional symptoms suggest dynamic mass effect, as early recognition and intervention are essential for optimizing outcomes.