Acrodermatitis dysmetabolica in an infant with maple syrup urine disease.

Acrodermatitis dysmetabolica (AD) is a rare, newly termed, and poorly understood disease that appears to be clinically similar to acrodermatitis enteropathica (AE). Both diseases are characterized by the triad of periorificial and acral dermatitis, diarrhoea, and alopecia. Unlike AE, which is caused by zinc deficiency, AD is caused by numerous metabolic disorders. One such disorder is maple syrup urine disease (MSUD), a genetic deficiency of branched chain α-ketoacid dehydrogenase, the enzyme that degrades the branched-chain amino acids (BCAAs) isoleucine, leucine and valine. Treatment involves restricting BCAAs to prevent accumulation. We report a case of an infant being treated for MSUD, who developed the triad of AE/AD after a period of poor BCAA formula intake. The child was found to have low isoleucine and normal zinc levels. Increasing the isoleucine dose improved the eruption, thus the diagnosis of AD secondary to isoleucine deficiency was made. This case emphasizes the importance of carefully balancing BCAA levels while treating MSUD, as deficiency can precipitate AD.