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Methaemoglobinaemia due to food protein-induced enterocolitis syndrome

CASE PRESENTATION A 25dayold term infant presented with fever, diarrhoea and 10% wt loss since birth (figure 1A) and 80% oxygen saturation in ambient air. His heart rate was 178 beats/min and blood pressure was 64/45 mmHg. Blood tests revealed a pH of 7.0, and bicarbonate, lactate and methaemoglobin levels of 6.2 mmol/L, 5.2 mmol/L, and 21%, respectively. After rehydration with fluid for shock, administration of sodium bicarbonate and stopping formula milk, his skin colour improved (figure 1B), and his methaemoglobin level decreased to 4.3% without intravenous methylene blue administration. After resuming formula milk feeding, diarrhoea and methaemoglobinaemia recurred, and the stool haemoccult test was positive. Test results for IgE to milk formula and casein were negative. He was diagnosed with food proteininduced enterocolitis syndrome (FPIES). After switching to extensively hydrolysed formula, he recovered and has not experienced recurrence of diarrhoea or methaemoglobinaemia. Methaemoglobin is a dysfunctional haemoglobin in which ferrous iron is oxidised to ferric iron. Infants aged <3 months are particularly susceptible to acquired methaemoglobinaemia because foetal haemoglobin is more readily oxidised and NADH diaphorase activity is lower than that in adults. FPIES is a nonIgEmediated food hypersensitivity disorder that typically presents with profuse vomiting and diarrhoea in a young infant fed with cows’ milk or soy formula. 4 Methaemoglobinaemia results from increased haeme oxidation caused by increased intestinal nitrites. FPIES should be considered in the differential diagnosis in infants aged <3 months who present with cyanosis and diarrhoea.