Methaemoglobinemia in paediatrics: a complex diagnostic journey

Methaemoglobinemia is a potentially life-threatening condition in which the heme iron is oxidised from the ferrous (Fe²⁺) to the ferric (Fe³⁺) state, leading to a left shift of the oxygen-dissociation curve and impaired oxygen delivery to the tissues. It can be either acquired through exposure to certain drugs or chemicals or inherited due to genetic mutations affecting enzymes like cytochrome b5 reductase.We report a case of an adolescent who presented with a persistent cough and unremarkable physical examination, making diagnosis challenging. A low SpO₂ level that did not improve with supplemental oxygen prompted further testing, leading to the diagnosis of methaemoglobinemia caused by cytochrome b5 reductase deficiency. The case highlights the complexities of diagnosing methaemoglobinemia, especially in the absence of classic symptoms like cyanosis. It underscores the importance of thorough clinical assessment in atypical cases and the need for heightened awareness of rare conditions.