Myasthenia gravis associated with thymic neoplasia in a cat

To describe acute myasthenia gravis (MG) in the postoperative period following removal of a thymoma in an adult cat. A 6-year-old spayed female domestic short haired cat weighing 6.4 kg was referred for workup and treatment of a cranial mediastinal mass. Thoracoscopic biopsies confirmed the diagnosis of thymoma. Median sternotomy was performed and approximately 95% of the mass was surgically excised. Postoperatively the cat became remarkably weak and hypercapneic. A presumptive diagnosis of MG was made following a positive response to edrophonium injection (Tensilon test). An elevated serum acetylcholine receptor antibody level was consistent with a diagnosis of MG. Initial treatment consisted of neostigmine, followed by corticosteroids and pyridostigmine. The cat responded well to therapy. This report describes a rare syndrome of postoperative weakness due to development of MG following incomplete removal of a thymoma. Post-thymectomy weakness associated with MG has been reported in dogs and is not well described in cats.