Methotrexate Toxicity Masquerading Section as Systemic Lupus Erythematosus Flare: A Case Report

A 36-year-old woman with Rheumatoid Arthritis (RA) and class V lupus nephritis presented with fever, dysphagia and oral mucosal bleeding. She had been prescribed Methotrexate (MTX) 15 mg weekly but used it irregularly-almost daily-for four months. On examination, she had oral ulcers, reduced mouth opening, diffuse hair thinning, and erythematous papules. Laboratory findings revealed severe pancytopenia, elevated liver enzymes, and an increased MTX level. Complement levels were normal and antidsDNA negative, making a Systemic Lupus Erythematosus (SLE) flare unlikely. The diagnosis of MTX toxicity was confirmed. She was managed with immediate MTX withdrawal, folinic acid rescue (15 mg i.v. every six hours for three days), blood transfusions, and supportive care. Her counts normalised, and mucositis resolved within two weeks. This case emphasises the diagnostic challenge in differentiating drug toxicity from disease flare in autoimmune patients and underscores the need for strict adherence to MTX monitoring guidelines.