Demyelinating Disease

Myelin sheath is the protective covering that surrounds the axons of the nerve fibers present in the body. It helps nerve signals travel faster along the axons and increases the efficiency of their conduction. The myelin sheath for the nerve cells of the central nervous system is formed by oligodendrocytic cells. In contrast, Schwann cells are responsible for myelinating the nerve cells of the peripheral nervous system. Demyelinating diseases occur when the myelin sheath of the central nervous system or the peripheral nervous system is damaged, but the axons are preserved. Due to the loss of the myelin sheath, several clinical deficits are seen due to the effect on the transmission of electrical impulses. Later, severe neurological conditions can develop because of increased damage and, in turn, slow impulses.

The cause of demyelination of the nerve fibers can be some pathological processes that induce inflammation and thus cause damage to the myelin, such as;

●     Immune-mediated destruction of myelin – in which your body’s immune cells start attacking your tissues.

●     Response to infections

●     Toxin exposure

●     Loss of oxygen

●     Physical compression

Several nutritional deficiencies can also induce demyelination. In addition, certain inherited disorders may also affect the synthesis of myelin components and are discussed as metabolic disorders.

Demyelinating diseases may be;

Demyelinating myelinoclastic – in which the myelin is destroyed.

Dysmyelinating leukodystrophic – wherein the myelin formed is abnormal.

Demyelinating diseases are also classified into types according to where they occur and their underlying causes.

In the Central nervous system

●     Multiple sclerosis

It is caused by an autoimmune response against the myelin sheath and the oligodendrocytes (cells that produce myelin). Multiple sclerosis is the most common demyelinating myelinoclastic disease of the central nervous system. After an autoimmune attack, inflammation and scarring occur at multiple sites in the CNS. The patient may present unilateral visual impairment if the optic nerve is involved. Furthermore, he may have vertigo, ataxia, and nystagmus.

●     Neuromyelitis Optica

It is also known as Devic’s disease. Its cause is bilateral optic neuritis and can involve spinal cord demyelination. After which, there is necrosis in the damaged area. The patient’s eyes, arms, and legs may be affected, leading to blurred vision, loss of sight, weak limbs, bowel conditions, uncontrollable hiccups, etc.

●     Central pontine myelinolysis

The demyelination, in this case, is most likely caused by an electrolyte imbalance; more specifically, sodium levels rise, and osmolar imbalance damages the oligodendrocytes. It causes weakness in both arms and legs, which may be fatal and lead to ‘locked-in syndrome’ in which the person is fully conscious yet unresponsive.

●     Acute disseminated encephalomyelitis

In this condition, a viral infection is the cause of demyelination and is presented by symptoms such as headache, fatigue, and coma. About 20% of the patients die while the rest recover completely.

In the peripheral nervous system:

●     Guillain-Barre syndrome

It is caused by an attack on the peripheral nerves, characterized by weakness beginning in the legs, which ascends to the arms. It can be fatal if breathing is involved. It also involves deep tendon reflex loss and loss of pain sensation.

●     Charcot-Marie-Tooth disease

It is an inherited condition that involves the peripheral nerves. Your legs and feet are majorly involved in losing sensation and muscle mass and may feel weak.

In most of the United States, approximately 1 in 500 persons are affected by some demyelinating disease. Out of these, about 400,000 people have multiple sclerosis. In contrast, 4000 to 8000 people are said to be affected by neuromyelitis optica.

The risk factors for the disease include;

●     Genetics

●     Environmental factors such as chemical exposure.

●     Low vitamin D levels (because it is an immune modulator).

●     Stress has an impact on the progression of multiple sclerosis.

 Different demyelinating diseases are presented with different symptoms, but some signs are persistent in almost all of the conditions. These are listed below;

●     Diplopia (blurred double vision)

●     Ataxia (clumsy voluntary movements)

●     Loss of sensation

●     Loss of vision

●     Nystagmus

●     Fatigue and muscle spasms

●     Dysarthria (difficulty speaking)

●     Dizziness

Some of the demyelinating diseases can be diagnosed by;

MRI scan – reveals plaques, which are areas of demyelination.

Lumbar puncture – CSF shows increased immune cells.

Electroencephalography – electrical potentials are used to detect a stimulus.  

Although multiple sclerosis stands as the most common demyelinating disorder, various other conditions are considered, including;

●     ADEM (Acute Disseminated Encephalomyelitis).

●     Optic neuritis

●     Transverse myelitis

●     Systemic lupus erythematosus

●     CNS vasculitis

There is no such treatment that cures demyelination, but its progression can be slowed, and the symptoms can be eased. The treatment is patient-specific and depends upon the severity of symptoms. It can include;

●     Medications

●     Physical therapy

●     Occupational therapy

●     Rehabilitation therapy

●     Immunosuppression

●     Supplementation with vitamin B12 and copper.

Medications

The medications used vary according to the condition. They may be;

●     Immunosuppressive like azathioprine, methotrexate, or immunomodulatory agents may slow the progression of the disease.

●     Glucocorticoids.

Prognosis depends on the disease diagnosed. In multiple sclerosis, the life expectancy of the patients decreases by 5 to 10 years as compared to the unaffected people. About 60 to 70% of patients with central pontine myelinolysis recover, and others experience varying degrees of disability.  In transverse myelitis, the patient can start recovering within 1 to 4 months of getting the disease. 

Some lifestyle changes can help manage the pain effectively, like smoking cessation, physical exercise, increased rest, and healthy dietary changes.