methemoglobinämie

Methemoglobinämie is a blood disorder characterized by an elevated level of methemoglobin in the blood. Methemoglobin is an oxidized form of hemoglobin, the protein in red blood cells responsible for carrying oxygen. In methemoglobin, the iron atom in the heme group is in the ferric (Fe3+) state, whereas in normal hemoglobin, it is in the ferrous (Fe2+) state. This alteration prevents hemoglobin from binding and releasing oxygen effectively, leading to a reduced oxygen-carrying capacity of the blood.

The condition can be congenital, resulting from inherited enzyme deficiencies such as cytochrome b5 reductase deficiency, or acquired. Acquired methemoglobinämie is typically caused by exposure to certain drugs, chemicals, or toxins. Common culprits include certain anesthetics like prilocaine, antimicrobial agents like dapsone, and nitrates found in contaminated well water or certain foods.

Symptoms of methemoglobinämie vary depending on the concentration of methemoglobin. Mild cases may be asymptomatic or present with slight cyanosis (a bluish discoloration of the skin and mucous membranes). As levels increase, symptoms can include headache, dizziness, fatigue, shortness of breath, and rapid heart rate. Severe methemoglobinämie can lead to confusion, seizures, coma, and even death if left untreated. Diagnosis is made through blood tests that measure methemoglobin levels. Treatment involves removing the causative agent and, in more severe cases, administering methylene blue, which acts as a reducing agent to convert methemoglobin back to normal hemoglobin.