Acute heart failure in an infant with methylmalonic acidemia: a diagnostic and therapeutic challenge.

Methylmalonic acidemia is characterized by the inability to convert L-methylmalonyl-CoA to succinylCoA, resulting in the accumulation of methylmalonic acid in the blood and/or urine. In its chronic form, it can cause cardiomyopathy with impaired cardiac function. Its management is based on several pillars; the most important is intramuscular hydroxycobalamin supplementation, which serves as a cofactor for methylmalonyl-CoA mutase. We present the case of a 6-month-old girl who was admitted to the emergency department with signs of heart failure. A multidisciplinary evaluation was performed to determine the etiology, and methylmalonic acidemia was diagnosed. We also report a novel route of administration for hydroxycobalamin in this condition (subcutaneous). We present the diagnostic approach and therapeutic challenges in this patient, given that the usual route of administration of hydroxycobalamin was contraindicated due to her comorbidities.