methemoglobinémia

Methemoglobinemia is a blood disorder in which the body has too much methemoglobin, a form of hemoglobin. Hemoglobin is a protein in red blood cells that carries oxygen from the lungs to the rest of the body. Methemoglobin is produced when the iron in hemoglobin is oxidized from the ferrous (Fe2+) to the ferric (Fe3+) state. This ferric iron cannot bind oxygen, reducing the oxygen-carrying capacity of the blood.

There are two main types of methemoglobinemia: congenital and acquired. Congenital methemoglobinemia is a rare, inherited condition caused by genetic mutations affecting the enzymes involved in maintaining hemoglobin in its ferrous state, most commonly cytochrome b5 reductase. Acquired methemoglobinemia is more common and can be caused by exposure to certain drugs, chemicals, and toxins. Examples include nitrates, nitrites, certain anesthetics like benzocaine and prilocaine, and antimalarial drugs. Ingesting contaminated water or food, particularly in infants, can also lead to acquired methemoglobinemia.

Symptoms of methemoglobinemia vary depending on the level of methemoglobin in the blood. Mild cases may present with bluish discoloration of the skin and mucous membranes (cyanosis), headache, and fatigue. Higher levels can lead to shortness of breath, dizziness, confusion, seizures, and even death if left untreated. Diagnosis is typically made through blood tests that measure the percentage of methemoglobin. Treatment for acquired methemoglobinemia involves administering methylene blue, which helps to convert methemoglobin back to normal hemoglobin. Congenital forms often require ongoing management rather than a cure.