Myasthenia Gravis and Thymoma

Thymoma is the most common tumor of the anterior mediastinum. Approximately 20%-30% of patients with a thymoma develop myasthenia gravis (MG), and an additional one third may possess positive acetylcholine receptor (AChR) antibodies without MG. Historical estimates suggest that thymoma associated MG (TAMG) represents roughly 15%-20% of MG patients, although the proportion of TAMG has been decreasing. Virtually all TAMG patients are seropositive for AChR antibodies. In comparison to MG without thymoma, TAMG is mostly generalized and more refractory to treatment. Chest CT with contrast is the imaging modality of choice in evaluating thymoma, while MRI and PET scan may have an ancillary role in defining tumor invasiveness, staging and further differentiating thymoma from other mediastinal masses. Surgical resection should be considered for all patients with thymoma, regardless of MG status as all thymomas are malignant. Minimally invasive surgery appears equally efficacious as sternotomy for patients with early stage thymoma, and has become more prevalent due to its lower complication rates. Preoperative optimization with intravenous immunoglobulin or plasmapheresis is unnecessary in patients with stable MG. New onset MG could occur in thymoma patients following thymectomy, and the presence of AChR antibody preoperatively may be a predictive risk factor. Patients with advanced stage thymoma may require neoadjuvant or adjuvant chemotherapy and/or radiation, typically managed in a multidisciplinary setting. The recurrence rate of thymoma is mainly dependent upon its pathological stage, and worsening myasthenic symptoms may herald a recurrence of thymoma.