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METHEMOGLOBINEMIA

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METHEMOGLOBINEMIA

Methemoglobinemia is a blood disorder characterized by elevated levels of methemoglobin in the blood.

  • Methemoglobin is a form of hemoglobin, which is the protein in red blood cells that carries and distributes oxygen to the body
  • Normally, hemoglobin carries oxygen and then releases it to all tissues and organ that needs it to survive throughout the body
  • Instead of normal hemoglobin, people with methemoglobinemia have an abnormal form called methemoglobin, which carries oxygen around the body but doesn’t release it to the tissues
  • This can result in tissue hypoxia, a condition in which the body or a region of the body is deprived of adequate oxygen
  • Cases of severe methemoglobinemia can lead to shock, seizures, and even death

TYPES AND CAUSES

There are two types of methemoglobinemia:

Congenital/inherited methemoglobinemia is caused by a genetic defect inherited from parents. This genetic defect leads to a deficiency of a certain enzyme that is responsible for converting methemoglobin to hemoglobin.  This enzyme is called cytochrome b5 reductase. There are three types of congenital methemoglobinemia, they are:

  • Type 1, also called erythrocyte reductase deficiency, occurs when the red blood cells lack the enzyme,
  • Type 2 inherited, also called generalized reductase deficiency, occurs when the enzyme doesn’t work in the body
  • Hemoglobin M disease occurs when the hemoglobin protein itself is defective

Acquired methemoglobinemia is more common than the inherited form and it is caused by exposure to certain medications, foods, or chemicals. People with the congenital form have a higher chance of developing the acquired type. But most people who acquire the condition don’t have a congenital problem. If left untreated, acquired methemoglobinemia can lead to death.

Babies are more susceptible and can get the acquired form from:

  • Contaminated well water
  • Benzocaine (found in over-the-counter products that are used to soothe a baby’s gum from teething)
  • Solid foods that may contain too many nitrates, including carrots, beets, spinach, squash, or green beans.

Adults can get the acquired form:

  • After having medical procedures where certain tropical anesthetics, such as benzocaine, lidocaine, and prilocaine are sprayed on the skin, using certain antibiotics
  • Using certain antibiotics including dapsone and chloroquine
  • Using antimalaria drugs

SYMPTOMS

Symptoms vary according to type and the level of methemoglobin in the blood. The main symptoms are:

  • Bluish color of skin, especially around the lips, fingers, and feet
  • Chocolate-brown colored blood

As the level of methemoglobin increases, symptoms continue to get serious and may include:

  • Shortness of breath
  • Nausea
  • Headache
  • Rapid heart rate
  • Loss of consciousness
  • Confusion
  • Fatigue or lack of energy
  • Seizures
  • Dizziness

DIAGNOSIS AND TREATMENT

To make a diagnosis, the doctor will carry out a blood test to check the level of functional hemoglobin in the blood.

Other diagnostic procedures may include:

  • An examination of blood color
  • Tests to check enzymes
  • Pulse oximetry to check the oxygen levels in the blood
  • Blood levels of nitrites and other drugs
TREATMENT

Mild cases of the condition do not usually require any treatment. The doctor will advise avoiding the substance that caused the problem.

In severe cases, the first treatment is infusion with methylene blue. The doctor may then prescribe ascorbic acid to reduce the level of methemoglobin.

People who don’t respond to methylene blue may need a blood transfusion