Methaemoglobinaemia as an Alternative Diagnosis for Shortness of Breath: A Case Report.

Methaemoglobinaemia is rarely considered as a differential diagnosis in patients presenting with shortness of breath and cyanosis. It can occur due to either congenital or acquired causes. The effect of medication is an important consideration as an acquired cause of methaemoglobinaemia, and if the diagnosis is missed, it may result in a fatal outcome. This scenario highlights the importance of awareness through thorough history-taking and careful review of investigations. Dapsone (4,4'-diaminodiphenyl sulfone) was identified as the main contributing factor in this case, and the symptoms resolved following its immediate discontinuation, with an improvement in oxygen saturation and a reduction in methaemoglobin levels.