A rare case of acquired methemoglobinemia associated with alkaptonuria.

We herein present a rare case of acquired methemoglobinemia associated with alkaptonuria. Alkaptonuria is a congenital error of metabolism caused by the deficiency of homogentisic acid oxidase, which subsequently results in the accumulation of homogentisic acid (HGA) in body tissues. As renal dysfunction progresses, the level of HGA excretion in the urine decreases and the blood concentration of HGA increases. HGA oxidizes oxyhemoglobin to methemoglobin, which can induce multiple organ failure accompanied by tissue hypoxia, intravascular hemolysis and metabolic acidosis. The mortality of this disease is high when alkaptonuria is associated with the presence of methemoglobinemia; therefore, treatment should be carefully planned in such cases.