metyhemoglobinemian

Methemoglobinemia is a blood disorder in which an abnormal amount of methemoglobin is present in the blood. Methemoglobin is a form of hemoglobin that contains ferric iron (Fe3+) instead of ferrous iron (Fe2+). This altered form of hemoglobin cannot bind and transport oxygen effectively. Normally, methemoglobin is present in very small amounts and is rapidly converted back to functional hemoglobin by enzymes in red blood cells. In methemoglobinemia, this conversion process is impaired, leading to an accumulation of methemoglobin.

Symptoms of methemoglobinemia depend on the level of methemoglobin in the blood. Mild cases, with less than 10% methemoglobin, may be asymptomatic. Higher levels can cause cyanosis (a bluish discoloration of the skin and mucous membranes), headache, fatigue, dizziness, and shortness of breath. Severe methemoglobinemia, with levels above 50%, can lead to seizures, coma, cardiac arrhythmias, and death.

Methemoglobinemia can be congenital or acquired. Congenital methemoglobinemia is typically caused by genetic defects in the enzymes responsible for reducing methemoglobin, most commonly cytochrome b5 reductase deficiency. Acquired methemoglobinemia is more common and is usually caused by exposure to certain drugs, chemicals, or toxins. Examples include nitrates, nitrites, dapsone, and certain local anesthetics.

Diagnosis is made through blood tests, specifically measuring the methemoglobin level. Treatment depends on the cause and severity. For mild cases caused by medications, discontinuing the offending agent may be sufficient. For more severe cases, intravenous administration of methylene blue is the primary treatment, as it acts as a cofactor to convert methemoglobin back to hemoglobin. In severe or refractory cases, blood transfusions may be considered.