Background Methotrexate is an antifolate antimetabolite that inhibits the activity of dihydrofolate reductase by acting as a false substrate, which leads to defects of DNA synthesis, specifically the inhibition of purine and pyrimidine synthesis. Thus, methotrexate is a powerful agent for treating autoimmune diseases and cancer. In general, methotrexate is thought to be cardioprotective and reports of methotrexate-induced cardiomyopathy are rare. We present a case of methotrexate-induced severe cardiotoxicity diagnosed by exclusion of all other potential causes. Case presentation The patient was a 54-year-old Caucasian man presenting to an outside hospital with a chief complaint of abdominal pain and bloating who reported taking methotrexate up to 20 mg per week for systemic sclerosis. After a transthoracic echocardiogram found a left ventricular ejection fraction of 10% and coronary catheterization demonstrated no significant disease, he was transferred to our hospital for advanced heart failure therapies. His condition deteriorated, and he was eventually placed on veno-arterial extracorporeal membrane oxygenation. Owing to a lack of an identifiable etiology of cardiac failure, toxicology consultation recommended 24 hours of intravenous leucovorin therapy to overcome any residual and potentially cardiotoxic methotrexate still in his system. Over the next 5 days, his cardiac function improved daily, such that on day 5 of extracorporeal membrane oxygenation, he had a left ventricular ejection fraction of 40% and was able to be decannulated. Two days later, his ejection fraction improved to 60% and normal right ventricular function. Initially, his renal function improved while on extracorporeal membrane oxygenation, but over the next week deteriorated such that he required intermittent hemodialysis until hospital discharge. Conclusions After a process of elimination, the most likely cause of this patient’s acute decline and rapid recovery of bi-ventricular function was methotrexate toxicity. Leucovorin may have aided the reversal of methotrexate toxicity.

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