Methemoglobinemia

Methemoglobinemia presents distinct signs and symptoms depending on its blood concentration level. The normal concentration of methemoglobin in the blood is only 1%, beyond which pathologies may already set in to play if left unabated.

The following system-wise physical presentations are commonly seen in patients suffering from methemoglobinemia:

• General Appearance: Patients may present with pallor and confusion due to the underlying anemia and inadequate brain oxygenation.
• Integumentary system: The bluish discoloration of the skin or cyanosis represents the heralding sign because it appears at a low desaturation level of more than 1.5% plasma methemoglobin. This could be the only presenting sign for methemoglobinemia upon birth.
• Head and neck: Pallor of the conjunctiva may mean severe anemia which could mask the cyanotic signs of methemoglobinemia.
• Chest and heart: Patients may complain of shallow breathing and bradyarrhythmia when methemoglobin becomes severe at blood levels exceeding 50-70%.
• Abdomen: Metabolic acidosis may ensue and destabilize electrolytes and cause functional constipation, ileus and abdominal distention.
• Extremities: Muscle weakness and fatigue due to lack of cell oxygenation may be observed in cases of methemoglobinemia. Thread like pulses are noticeable with late complications of arrhythmia.
• Neurologic: When methemoglobin levels exceeds 50% in the serum, signs of delirium and coma may start to ensue because of the chronic oxygen deprivation of the brain.

Symptoms

Observing the symptoms is often the fastest way to determine the decline and severity of the methemoglobinemia. Observing vital signs such as oxygen saturation and pulse can be vital in the case of rapid onset following exposure to a toxin or chemical.

Laboratory tests

In cases of hereditary methemoglobinemia, arterial blood gas (ABG) levels are typically helpful in diagnosing the condition.
In cases of acquired methemoglobinemia, some laboratory tests that would be performed would include:

• Complete blood count (CBC)
• Arterial blood gases (ABGs)
• Peripheral blood smear 
• Lactate dehydrogenase (LDH)
• Reticulocyte count 
• Bilirubin
• Pulse oximetry
• Haptoglobin

Imaging Studies

Imaging studies would not typically be necessary, but might be done later in the course of the condition to determine the extent of damage to organ systems such as the heart or neurological system.

The most commonly mentioned treatment is the use of methylene blue, which is a reduction compound [10]. 

The prognosis of methemoglobinemia is dependent on several factors. The severity of the case is one factor. Mild cases tend to have a better prognosis.

When the condition is caught early, as in a case study following use of a topical anaesthetic, aggressive intervention can result in a favourable prognosis. Methemoglobin levels at or above 70% have higher rates of fatalities and involve more extensive organ damage that can be irreversible, resulting in a much less favourable prognosis.

Complications:

The three main complications are shock, seizure, and death. There has been evidences linking maternal methemoglobinemia from prenatal nicotine exposure to unexplained fetal and infant death [9].The risk and extent of complications depends on the severity of the case.

Methemoglobinemia can be acquired through exposure to many different things including dyes, silver nitrates, nitrous oxide, local anaesthetics [1], dapsone [2], and other chemicals.

One case report describes the reaction of a 60-year-old patient to a topical anaesthetic sprayed in the throat prior to intubation for surgery [3]. Another case study similarly reported methemoglobinemia acquired post-surgically in a 36-year-old patient who received a topical anaesthetic for diagnostic purposes [4].

Hereditary methemoglobinemia has two types. In one type the red blood cells lack a necessary enzyme. This is due to the genetic defect that is transmitted via an autosomal-recessive gene that renders the cytochrome P5 reductase deficient and ineffective in reducing methemoglobin in the plasma [5]. In the second type the enzyme is present but fails to work in the body.

Incidence

Two types of methemoglobinemia exist: hereditary and acquired. The incidence varies based on type. Acquired methemoglobinemia is typically due to exposure to exposure to certain drugs or toxins.

Age

Inherited methemoglobinemia can be present at birth, while acquired methemoglobinemia can occur at any time during one’s life, particularly after exposure to certain chemicals or toxins.

Sex

There are no major differences in occurrence of methemoglobinemia between males and females, except in the case of individuals with G6PD deficiencies since this deficiency is x-linked.

Methemoglobinemia occurs when methemoglobin levels are increased in the body. Even though methemoglobin is a form of haemoglobin, it is unable to carry and/or deliver oxygen to cells and tissues. This condition does not preclude a drop in erythrocyte count but is functionally anaemic; thus, methemoglobinemia can essentially lead to functional anemia [6].

A deficient pathway in the reduction of methemoglobin to haemoglobin plays a hand in the pathophysiology of methemoglobinemia [7]. Without oxygen cells and tissues become hypoxic and can die off if the condition is not reversed. When cells of the cardiac and neurological system begin to die off, symptoms such as bluish colouring of the skin, seizures, and shortness of breath can occur. At methemoglobin levels beyond 15%, cardiac and neurologic signs wills start to surface while levels above 70% may no longer be compatible with life [8].

Types

Hereditary methemoglobinemia is passed down from a parent. In this type, there are two subtypes. In the first type red blood cells lack the necessary enzyme cytochrome b5 reductase. In the second type the enzyme is present but does not work in the body as it should.

Methemoglobinemia is a complex condition. Acquired methemoglobinemia cannot typically be predicted and prevented ahead of time. Hereditary methemoglobinemia can be potentially prevented through genetic counselling for couples with a family history of methemoglobinemia who are considering having children of their own.

Methemoglobinemia is a disorder of the blood where methemoglobin, which is a type of hemoglobin, is found in abnormally high amounts in the blood. Anything over one percent is considered to be a high concentration of methemoglobin. Hemoglobin’s important task is distributing oxygen to the cells of the body.

Methemoglobin, however, cannot release oxygen, which results in less oxygen getting to vital organs and tissues, resulting in hypoxia, meaning the cells are not getting enough oxygen to function properly, and are at risk of dying due to this complication.

Symptoms are proportional to the percentage of methemoglobin. Generally, above the level of 15% patients experience cardiac and neurological symptoms and levels over 70% tend to be fatal.

Definition

Methemoglobinemia is clinical disease where methemoglobin levels are abnormally high in the blood stream.

Cause

Methemoglobinemia can be acquired through exposure with medications like anaesthetics, dapsone, dyes and other compounds. An autosomal-recessive gene causing cytochrome P5 reductase deficiency is the cause of inherited methemoglobinemia.

Symptoms

Cyanosis, headache, fatigue, seizures, mental retardation, and failure to thrive among infants may occur.

Diagnosis

Methemoglobin is confirmed by arterial blood gas (ABG) studies and pulse oximetry.

Treatment and follow-up

Patients suffering from severe methemoglobinemia can benefit from the administration of methylene blue dyes that reverses the methemoglobin in the system. Special precautions are taken for G6PD patients for they are unable to metabolize the dye.

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