Congenital methaemoglobinaemia: a rare cause of cyanosis in an adult patient.

Cyanosis is a physical finding that can occur at any age but presents a great challenge as the causes are multiple and varied. When patients present with cyanosis and dyspnoea that are unrelated to cardiopulmonary causes, methaemoglobinaemia should be considered as a possible diagnosis although rare. Methaemoglobinaemia can be asymptomatic even when methaemoglobin (metHb) levels are as high as 40% of the total haemoglobin values. Although acquired methaemoglobinaemia caused by environmental oxidizing agents is common; congenital deficiency of the innate reducing enzymes is so rare that very few cases have been documented. We report this case of type I congenital methaemoglobinaemia.