Multimodal immunotherapy ameliorates myasthenia gravis preceded by thymoma-associated multiorgan autoimmunity.

Thymoma-associated multiorgan autoimmunity (TAMA) is a rare autoimmune disorder associated with thymoma that causes a pathology similar to graft-versus-host disease (GVHD) targeting the skin, digestive organs, and liver. Herein, we report the case of a 38-year-old male with myasthenia gravis (MG) preceded by TAMA. The patient developed intractable diarrhea 2 years before admission. Subsequently, dysphagia, dysarthria, and left blepharoptosis were observed. The patient was admitted to the hospital because of fever and dyspnea, was positive for anti-AChR antibody, and chest-computed tomography revealed thymoma, which led to the diagnosis of thymoma-related MG. Biopsied specimens from the sigmoid colon revealed apoptotic colonopathy with lymphocyte-rich lamina propria. Immunohistochemical staining revealed that the infiltrating cells were predominantly labeled with anti-CD3-antibody. The patient did not show skin lesions or liver dysfunction. Therefore, TAMA limited to the gastrointestinal tract was diagnosed. Although TAMA typically has a poor prognosis, immediate multimodal immunotherapy for MG was successful, resulting in a good outcome for TAMA of this case. TAMA is caused by the inability of the thymoma to suppress self-reactive T lymphocytes, which subsequently leads to a disease that is clinically indistinguishable from GVHD. Based on the characteristics of this case, limited gastrointestinal tract involvement in TAMA without lesions in other organs may lead to a favorable prognosis. TAMA cases lacking skin lesions may present with nonspecific gastrointestinal or liver disease. If a patient with thymoma-associated MG has gastrointestinal symptoms such as diarrhea, TAMA should be considered, and the diagnosis should be made early by pathological evaluation of gastrointestinal tissues.