A rare cause of cyanosis: Congenital methemoglobinemia
Congenital Methemoglobinemia is a rare condition that may mimic congenital heart diseases. There are two types of congenital Methemoglobinemia. The type I is usually benign. The enzyme deficiency is limited to red blood cells. Clinically, the patient presents cyanosis without neurological disorders. Whereas, in type II, cyanosis is associated with severe neurological impairment.

The patient is a 13-month-old girl, the first child of a first-degree consanguineous couple. The pregnancy was without complications. She was born at full term from vaginal delivery. Apgar's score was 9 at one minute and 10 at 5 minutes. Birth weight was 3300 g.

Since birth, parents noticed a cyanosis of the face that became more marked at the age of 5 months. Psychomotor development was normal. The infant was referred to our department by a general practitioner at the age of 13 months for exploration of cyanosis. The interview with the parents revealed that the mother worked in the manufacture of jewelry. The infant diet included vegetable purees containing carrots stored for more than 24 hours. The physical examination found normal weight, height, and head circumference. She had cyanosis.

Cardiac and pulmonary auscultation were both normal. The neurological examination was normal. Oxygen saturation was 94% in room air (she was crying). Chest X-ray and cardiac ultrasound were normal. The blood cell count showed polycythemia at 6 490 000/mm3, hemoglobin level was 12.7 g/dL. Electrophoresis of hemoglobin, renal, and hepatic status were normal. Methemoglobinemia and other differential diagnosis were considered such as congenital heart disease. The heart examination was normal.

However, the level of methemoglobin was very high. It was measured at 39.4% confirming the diagnosis. A specialized investigation concerning the products handled by the mother excluded a toxic cause. The correction of the methods of preparation and conservation of the diet did not improve the cyanosis. The diagnosis of recessive congenital methemoglobinemia type I was strongly suspected. The determination of the enzymatic activity of NADH cytochrome b5 reductase and DNA sequencing is not available in Tunisia. She did not develop neurological impairment on outcome, which improve the diagnosis of congenital methemoglobinemia type I.

The patient received an intravenous infusion of 1.2 mg per kg of methylene blue (MB) after eliminating glucose 6 dehydrogenase deficiency. Cyanosis disappeared immediately. The methemoglobin level dropped to 2.6%. Dietary measures were explained to parents. Four days after the medication, cyanosis reappeared, the methemoglobin level increased to 38.4%.

The patient received a second intravenous infusion of MB and then was put on vitamin C at a dose of 500 mg per day orally. After a 6 months of follow-up and vitamin C treatment, there was a clear improvement. She has mild cyanosis on exercise. Methemoglobin level was 10.9%. She showed no side effects of treatment.

Source: https://onlinelibrary.wiley.com/doi/10.1002/ccr3.4422?af=R
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