As many as 50% of patients with thymoma have MG, and approximately 15% of patients with MG have thymoma.4 MG is caused by autoantibodies to postsynaptic nicotinic acetylcholine receptors (anti-AChRs) at the neuromuscular junction, causing weakness of skeletal muscles. Some patients with thymoma-associated MG have an inflammatory myopathy of striated and cardiac muscles. Cardiac myositis may cause heart failure, cardiac arrhythmia, and sudden death.
Lambert-Eaton myasthenic syndrome
Lambert-Eaton myasthenic syndrome (LEMS) is an autoimmune disease characterized by reduced quantal release of acetylcholine from the motor nerve terminal. The patient with LEMS develops muscle weakness, myalgias, and fatigability. LEMS predominantly involves the proximal muscles of the legs. Unlike MG, LEMS spares the extraocular muscles. The muscle strength is reduced at rest and transiently improves with repetitive muscle action. LEMS is associated with an antibody to the presynaptic calcium channel. Underlying cancer is found in 50-60% of persons with LEMS. In individuals with LEMS, the most commonly reported tumor is small cell lung cancer; however, thymoma has also been one of the associated neoplasms.
Subacute sensory neuronopathy
Subacute sensory neuronopathy is a rare disorder associated with small cell lung cancer and other thoracic malignancies, including thymoma and esophageal carcinoma. The patient develops painful paresthesias in the lower extremities that may ascend to involve the trunk and face. Marked sensory loss can lead to truncal ataxia, although motor strength is normal. The characteristic destruction of the dorsal root ganglia is believed to be antibody mediated.
Red cell aplasia
Of patients with thymoma, 5% develop pure red cell aplasia; 10-50% of patients with red blood cell aplasia have thymoma. Thrombocytopenia, granulocytopenia, and autoantibody formation are sometimes observed. In two thirds of individuals with red cell aplasia, morphologically, the thymoma is the spindle cell variety. Approximately 30% of patients with the disorder resume normal hematopoiesis after thymectomy.
Common variable immunodeficiency (CVID) with thymoma, Good syndrome, and immunodeficiency with thymoma are characterized by hypogammaglobulinemia or agammaglobulinemia in association with thymoma. Thymoma is associated with approximately 10% of hypogammaglobulinemia cases, and combined humoral and cell-mediated immunodeficiency is often noted. Immunodeficiency has been demonstrated to occur years after thymoma resection.
Good described Good syndrome in 1954. The syndrome usually occurs in individuals aged 40-70 years and only rarely occurs in children. However, an 8-year-old boy reportedly developed fatal chickenpox 4 months after resection of a benign thymoma. The immunodeficiency in Good syndrome affects both T and B lymphocytes, typically manifested as low B-cell numbers and inverted CD4+/CD8+ cell ratio. The thymic tumors are usually of the spindle cell type and are benign. Good syndrome is associated with recurrent bacterial sinopulmonary infections, chronic diarrhea of unclear etiology, and opportunistic infections. Autoimmune disorders are also associated with these acquired immunodeficiencies.