A Clinical Case of Methotrexate Toxicity.

Methotrexate is a commonly prescribed immunosuppressant and chemotherapy agent, carefully monitored by healthcare providers due to its potential adverse effects. As a result, methotrexate toxicity is relatively rare. We present the case of a 79-year-old man followed in rheumatology for symmetrical polyarthralgia, who inadvertently took methotrexate 10 mg daily, instead of weekly, leading to methotrexate toxicity. The patient presented with erosive mucositis affecting the lateral tongue, buccal mucosa, and hard palate, as well as pustular lesions on the scalp (occipital and cervical regions) extending to the trunk. Laboratory findings revealed pancytopenia and transaminitis, and upper gastrointestinal endoscopy showed erythema and superficial ulcerations in the oropharyngeal region. Methotrexate was discontinued immediately, and the patient was treated with intravenous fluids, filgrastim, and supportive care. This case highlights the importance of early recognition of methotrexate toxicity, as well as the critical role of patient education. It underscores how easily a medication with numerous therapeutic benefits can cause serious adverse outcomes if not taken as prescribed. Effective communication between healthcare providers and patients is essential to ensure medication safety.