Early onset Methotrexate induced pneumonitis and concurrent leflunomide induced Aphthae: A Case report of severe toxicity in Rheumatoid Arthritis

Methotrexate is considered to be the mainstay treatment of Rheumatoid Arthritis. Still, one of the rare, life-threatening complications of its use is pulmonary toxicity, generally in the form of interstitial lung disease. We present a case of a 52-year-old male patient who developed a pattern of usual interstitial pneumonia within 1 month of taking a low dose of 7.5 mg of methotrexate per week. To further complicate the issue, the patient also complained of painful mouth ulcers, most probably due to leflunomide, which is associated with both pulmonary and mucosal toxicity. Interestingly, the patient didn’t have any major preexisting risk factors, and his respiratory examination was completely normal, as opposed to his imaging results. This indicates the need for early imaging studies such as computed tomography to detect abnormalities even in the presence of a normal systemic examination. Upon the clinical suspicion of possible methotrexate pneumonitis and due to oral ulceration, both drugs were withdrawn, and the patient was successfully switched to Sulfasalazine, with supportive measures including nutritional supplementation. This case report showcases a diagnostic challenge of distinguishing between rheumatoid arthritis associated interstitial lung disease and methotrexate pneumonitis, while considering the possible leflunomide toxicity. This case further points out the importance of vigilant monitoring of combination drug therapy and the early identification of adverse drug reactions to enhance patient safety and outcomes.
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