Methotrexate Toxicity-Induced Pancytopenia and Mucocutaneous Ulcerations in Psoriasis

Methotrexate (MTX) is a commonly used immunosuppressant and chemotherapeutic agent, widely prescribed for autoimmune diseases such as psoriasis, rheumatoid arthritis, and certain malignancies. It functions by inhibiting dihydrofolate reductase, leading to impaired DNA synthesis and cell proliferation. While generally well-tolerated, MTX has a narrow therapeutic index, and its adverse effects can be severe, including hepatotoxicity, pulmonary toxicity, and hematological complications such as pancytopenia. Pancytopenia involves the reduction of all three blood cell lines and can result in significant morbidity and mortality. The risk of MTX toxicity is notably higher in patients with renal impairment, as the kidneys are the primary route of drug excretion. Renal dysfunction can lead to the accumulation of MTX, enhancing its toxicity. Numerous studies and case reports have highlighted the risks of MTX toxicity, especially in patients with renal impairment. Pancytopenia can present insidiously, with symptoms such as mucosal ulcers, fever, and generalized weakness, making early detection crucial. We report a case of a male patient in his late 40s with a complex medical history, including psoriasis, insulin-dependent type 2 diabetes mellitus, chronic kidney disease (CKD) stage 3b, and coronary artery disease (CAD). The patient presented to the emergency department with a one-week history of fever, generalized weakness, mouth sores, and a five-day history of bilateral lower limb swelling and pain. Vital signs were stable, but physical examination revealed pallor, large ulcerative lesions in the buccal mucosa, and erythematous, scaly lesions on the lower limbs. The patient's medication history included methotrexate, which he had stopped two months prior but was inadvertently resumed at an increased dose two weeks prior to presentation. Laboratory findings revealed pancytopenia with worsening trends, prompting a bone marrow biopsy that showed hypocellular marrow. The patient's CKD likely exacerbated the MTX toxicity due to impaired drug clearance, leading to pancytopenia. Treatment included intravenous leucovorin, blood and platelet transfusions, and granulocyte-macrophage colony-stimulating factor (GM-CSF). Despite initial critical presentation, the patient showed significant improvement, with recovery of blood counts and resolution of symptoms. He was discharged with stable hemoglobin, platelet, and white blood cell counts.