Methemoglobinemia with an Oxygen Saturation Gap Secondary to Favism in a Newly Diagnosed Glucose-6-Phosphate Dehydrogenase Deficiency

Abstract: Glucose-6-phosphate dehydrogenase (G6PD) deficiency is the most common enzyme deficiency worldwide, with the highest prevalence in African, Asian, and Mediterranean populations, typically presenting with hemolytic anemia. On the other hand, methemoglobinemia is a potentially life-threatening condition that occurs when oxidative agents lead to the formation of methemoglobin. We report a 20-month-old boy presenting with a 1-day history of vomiting and fever, appearing pale and dehydrated but not in distress. He was found to be hypoxic, which did not improve despite oxygen supplementation. Initially, the family reported a history of thalassemia, but further investigation revealed that the child was a carrier only. Upon further questioning, the family confirmed that the child had consumed a large amount of fava beans 2 days before presentation. The child was never diagnosed with G6PD disease, and he had eaten fava beans on several occasions with no history of hemolytic anemia. Lab results revealed non-immune hemolytic anemia, and serial arterial blood gases showed elevated methemoglobin level, which improved and resolved after repeated blood transfusions; low G6PD level confirmed the diagnosis. This case was challenging due to the patient’s atypical presentation with gastroenteritis-like symptoms; he was then found to have severe anemia with asymptomatic and oxygen-refractory hypoxia. Favism was suspected after further detailed history was taken. Although rare, the co-occurrence of these conditions can be life-threatening. Recognizing the risk of worsening hemolysis when treating with methylene blue in patients with G6PD is crucial; hence, early consideration of G6PD disease can alter management and potentially improve the outcome.