New diagnosis of myasthenia gravis presenting as myasthenic crisis after radical thymectomy: a case report

Abstract

Myasthenia gravis (MG) is a well-known paraneoplastic syndrome associated with thymomas. It occurs secondary to the production of autoantibodies against acetylcholine receptors (AChR). This results in the reduced delivery of action potentials that generate muscular contractions. In its most extreme form, MG can present as a crisis resulting in respiratory failure requiring invasive ventilatory support. There are several known risk factors for patients with known MG to develop a post-operative crisis after thymectomy.It is recommended that patients diagnosed with thymoma be evaluated for MG prior to resection. However, most guidelines do not make any recommendations regarding screening with AChR antibody tests if there are no signs or symptoms of MG. In this case report, we present a patient with an incidental finding of a large anterior mediastinal thymoma with no signs or symptoms of MG. The patient subsequently develops bulbar symptoms and dyspnea necessitating readmission to hospital 2 weeks after surgery. This eventually culminated in cardiorespiratory arrest. This was confirmed to be secondary to a myasthenic crisis via AChR autoantibody testing. The patient was treated with intravenous immunoglobulin (IVIG), pyridostigmine and prednisone with good effect. The onset of myasthenic crisis after a surgical insult in known MG patients has been well documented. However, the development of myasthenic crisis in an asymptomatic patient with no history of MG has not previously been shown. This case report illustrates the need for more sensitive screening tools to detect MG in patients with thymoma. The routine use of AChR autoantibody testing as a screening tool in patients with thymoma even when asymptomatic and/or deemed low risk may help clinicians better prepare for possible MG flairs. Furthermore, surgeons should have a low threshold to suspect MG in patients after thymectomy regardless of time elapsed since surgery.