Methemoglobinemia: cyanosis and street methamphetamines.

Methemoglobin is a type of hemoglobin in which the ferrous ion has been oxidized to the ferric state. It is therefore incapable of combining with or transporting the oxygen molecule, which is replaced by a hydroxyl radical. Methemoglobinemia can be acquired or inherited. Most cases are acquired and are primarily due to exposure to certain drugs and chemicals, such as nitrates, nitrites, quinones, and chlorates. Inherited methemoglobinemia can result from a structural abnormality of the globin chains, or it can occur as a result of a red blood cell enzyme defect in which the methemoglobin formed cannot be converted back to the reduced form of hemoglobin. Methemoglobin is normally present in the blood in concentrations of 1 to 2 percent and its formation is reversible. I I came across a particularly interesting case of methemoglobinemia in which the patient had acute cyanosis.