Single Low-Dose Methotrexate and Vitamin B12 Deficiency-Induced Pancytopenia Causing Fatality: A Case Report.

Methotrexate (MTX), a commonly used disease-modifying antirheumatic drug, is generally considered safe at low cumulative doses. However, severe pancytopenia can occur even with doses as low as 10 mg, as illustrated by a fatal case in an older adult with chronic kidney disease (CKI) and vitamin B12 deficiency. Despite the low dose and lack of folate supplementation, the patient developed severe mucositis and pancytopenia leading to fatal complications. This case underscores the challenges in diagnosing and managing MTX-induced pancytopenia, especially in patients with comorbidities such as CKI and vitamin B12 deficiency.