Methemoglobinemia is a form of blood hemoglobin disorder and is also known as hemoglobin M disease and Erythrocyte reductase deficiency.
Hemoglobin found in RBC is a characteristic multi-subunit globular protein and is also a metalloprotein containing iron.
The protein chain in each subunit is bound to a non-protein heme group.
The iron ion in the heme group is normally in ferrous (Fe2+) state (hemoglobin) which binds readily to oxygen in lungs during respiration.
However certain deficiencies in the enzyme mechanisms, certain harmful chemicals, drugs and/or certain hereditary factors can cause iron ion to remain in ferric (Fe3+) state (methemoglobin) and in this state the heme group is incapable of binding to oxygen.
This ferric state of heme group leads to oxygen starvation of body tissues causing discoloration and cyanosis (methemoglobinemia).
Though some methemoglobin is present in normal persons (1-2%), any further increase can result in methemoglobinemia conditions.
Methemoglobinemia may be caused due to exposure to certain drugs, food products and chemicals; this is the acquired form.
Antibiotics like dapsone and chloroquine, anesthetics like xylocaine and benzocaine, aniline dyes, preservative nitrite food additives and excess consumption of nitrate containing foods, especially by children, can cause acquired methemoglobinemia.
Methemoglobinemia may also result due to deficiency in the inherited enzyme mechanisms.
There are two types of inherited forms and in type 1 there is erythrocyte reductase deficiency. This type is caused by recessive gene and both the parents have to contribute the faulty gene for inheritance.
In the type 2 methemoglobinemia there is generalized reductase deficiency (hemoglobin M disease) and in this form a child inherits the disease even if only one parent has the culprit gene.
The initial symptom of acquired methemoglobinemia is slow setting of bluish discoloration of skin showing cyanosis.
The condition may not set right even on administration of oxygen.
Further the patient may lack energy and have fatigue, palpitations, confusion and headache.
The patient may show cellular hypoxia and at methemoglobin levels of 70% or more death may occur.
In the hereditary forms cyanosis can be seen at birth or soon after.
There may be developmental delay, mental impairment, seizures and death.
In fair skin complexion the blemishes and discoloration is apparent whereas in dark skin conditions it may become tougher.
Hence, the actual cause of methemoglobinemia must be investigated and depending on the causative factors various remedial measures can be taken.