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PEDIATRICS Vol. 112 No. 2 August 2003, pp. e158-e161

EXPERIENCE AND REASON

Congenital Methemoglobinemia: A Rare Cause of Cyanosis in the Newborn—A Case Report

Shonola S. Da-Silva, MD*, Imran S. Sajan, MD* and Joseph P. Underwood, III, MS{ddagger}

* Division of Pediatric Critical Care Medicine, Children’s Regional Hospital, Cooper Hospital/University Medical Center, Camden, New Jersey
{ddagger} University of Medicine and Dentistry, Robert Wood Johnson Medical School, Camden, New Jersey

Cyanosis is a physical finding that can occur at any age but presents the greatest challenge when it occurs in the newborn. The cause is multiple, and it usually represents an ominous sign, especially when it occurs in association with neonatal sepsis, cyanotic congenital heart disease, and airway abnormalities. Cyanosis caused by abnormal forms of hemoglobin can also be life-threatening, and early recognition is mandatory to prevent unnecessary investigations and delay in management. Abnormal hemoglobin, such as hemoglobin M, is traditionally discovered by electrophoresis, so the newborn screen, which is mandatory in several states, is a useful tool for the diagnosis. Although acquired methemoglobinemia, caused by environmental oxidizing agents, is common, congenital deficiency of the innate reducing enzyme is so rare that only a few cases are documented in the medical literature around the world. We present a neonate with cyanosis as a result of congenital deficiency of the reduced nicotinamide adenine dinucleotide-cytochrome b5 reductase enzyme. This infant was found to be blue at a routine newborn follow-up visit. Sepsis, structural congenital heart disease, prenatal administration, and ingestion of oxidant dyes were excluded as a cause of the cyanosis by history and appropriate tests. Chocolate discoloration of arterial blood provided a clue to the diagnosis. A normal newborn screen and hemoglobin electrophoresis made the diagnosis of hemoglobin M unlikely as the cause of the methemoglobinemia (Hb A 59.4%, A2 1.8%, and F 38.8%). Red blood cell enzyme activity and DNA analysis revealed a homozygous form of the cytochrome b5 reductase enzyme deficiency. He responded very well to daily methylene blue and ascorbic acid administration, and he has normal growth and developmental parameters, although he shows an exaggerated increase in his methemoglobin level with minor oxidant stress such as diarrhea.

Key Words: cyanosis • methemoglobinemia • newborn • NADPH-cytochrome b5 reductase

Abbreviations: PRBC, packed red blood cell • NADH, reduced nicotinamide adenine dinucleotide

Received for publication Nov 25, 2002; Accepted Apr 21, 2003.




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