Unexplained acute severe methaemoglobinaemia in a young adult

This report describes the case of an otherwise healthy young adult female, who presented with a 12-h history of progressive bluish discolouration of l ips and limbs. She denied ingesting or inhaling any drug or substance. A hi gh Pa-O2 in the presence of 'cyanosis' and 'dark blood' led to suspicion of methaemoglobinaemia. Co-oximetry revealed the methaemoglobin level to be 4 7%. A urinary screen for drugs of abuse was negative and blood methaemoglob in reductase activity was within the normal range. The aetiology was traced to dapsone detected in the urine by gas chromatography/mass spectrometry. The therapeutic and diagnostic approach in such patients is discussed.