A case of myelodysplastic syndrome during treatment with methotrexate for rheumatoid arthritis

Methotrexate （MTX） is widely used as a treatment for rheumatoid arthritis. It is known to cause stomatitis and bone marrow suppression as side effects, but there have been no reports of myelodysplastic syndrome （MDS）. We report a case of severe oral and pharyngeal mucosal erosions and pancytopenia during oral MTX administration, which led to the diagnosis of myelodysplastic syndrome. The patient was an 87-year-old woman who had been taking MTX for rheumatoid arthritis for 7 years. She came to the hospital because of difficulty eating with stomatitis. She was treated with intravenous drip as an outpatient, but the condition did not improve and she was hospitalized 3 days later. After admission, MTX was stopped, but the erosions of the oral cavity and laryngeal mucosa got worse, and also pancytopenia was observed, so a bone marrow examination was performed. The results showed MDS. We continued symptomatic treatment, the pancytopenia and mucosal erosions gradually improved and the patient was discharged from the hospital. The pancytopenia and mucosal erosions improved after MTX was discontinued in this patient, suggesting that MDS developed due to the cytotoxic effect of MTX. Caution is required when treating an elderly person taking MTX who has stomatitis, as it may be a precursor to serious side effects such as myelosuppression and MDS.