An Overview of Demyelination

When the Protective Layer That Surrounds Nerves Is Impaired

Myelin degeneration

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SHUBHANGI GANESHRAO KENE

 

 

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Demyelination is loss of myelin, a type of fatty tissue that surrounds and protects nerves throughout the body. This condition causes neurological deficits, such as vision changes, weakness, altered sensation, and behavioral or cognitive (thinking) problems. 

Demyelination can affect areas of the brain, spinal cord, or peripheral nerves, and it occurs with a number of different medical illnesses. The most common demyelinating conditions are multiple sclerosis (MS) and peripheral neuropathy

A variety of medical treatments can be used for management of demyelinating medical illnesses, and the treatment is tailored to the specific condition.

Symptoms

Demyelination can occur at any age, but each demyelinating condition tends to affect certain age groups.

The symptoms of demyelination correspond to the area of the nervous system affected. For example, peripheral neuropathy affects the hands and feet in what is often described as a “stocking glove” distribution.

Demyelination affecting the lower spine or the spinal nerves causes sensory changes or weakness of the legs, and may also diminish bowel and bladder control. And demyelination in the brain can cause a variety of problems, such as impaired memory or decreased vision.

Common symptoms of demyelinating diseases include:

  • Loss of vision or diminished vision
  • Numbness or tingling of the hands, feet, arms, legs, or face 
  • Weakness of the arms or legs
  • Decreased coordination
  • Trouble walking
  • Problems chewing or swallowing
  • Slurred speech
  • Deceased bowel or bladder control
  • Problems with concentration
  • Impaired memory
  • Mood or behavioral changes
  • Fatigue

Depending on the condition, the symptoms of demyelination may come and go, or they may gradually worsen.

Many types of MS are characterized by episodic symptoms and substantial improvement in between episodes. Peripheral neuropathy tends to gradually worsen. In some demyelinating conditions, such as cerebral adrenoleukodystrophy (CALD) the effects do not improve, and can be fatal.

Causes

The symptoms of demyelination occur due to loss of myelin. Myelin sheaths insulate peripheral nerves as well as nerves in the brain, spinal cord, and eyes. Each eye has an optic nerve that controls vision. The myelin sheaths allow nerves to send signals efficiently.

When there is a deficiency or a sudden decrease in myelin, the nerves may not be able to function at all, resulting in the neurological deficits seen with demyelination.

Triggers

Demyelination is often caused by inflammation that attacks and destroys myelin. Inflammation can occur in response to an infection, or it can attack the body as part of an autoimmune process. Toxins or infections can also harm myelin or may interfere with its production. And a lack of myelin formation, can be seen with some nutritional deficiencies.

Risk Factors

There are many factors that can induce demyelination, including genetics, infections, toxicity, and nutritional deficits. Some conditions, like Guillain-Barre syndrome (GBS), can be idiopathic, which means that they can occur without a clear trigger.

Diagnosis

Demyelination is diagnosed using several different methods. A medical history and physical examination can often establish whether the brain, spine, optic nerves, or peripheral nerves are affected. However, sometimes the signs and symptoms can be confusing, and it may take some time to determine the type and cause of demyelination and to identify the specific illness.

Clinical Examination

When you are being evaluated for a demyelinating illness, your doctor will listen to your medical history and may ask details about how long you have had your symptoms, whether you ever experienced them before, and whether you have recently been sick with an infection.

Your doctor will likely ask you about other symptoms, such as pain, nausea, vomiting, or fevers. Your medical team will want to know about your history of other illnesses and your family medical history.

The physical exam will check your muscle strength, sensation, coordination, and ability to walk. Your doctor may check your vision and how your pupils react to light. You might have an ophthalmologic examination in which your doctor looks at your eyes with an ophthalmoscope to see if you have optic neuritis (inflammation and demyelination of the optic nerve).

Imaging

Brain or spine imaging such as magnetic resonance imaging (MRI) can often identify areas of demyelination. There are usually patterns of demyelination that correspond to different conditions.

Special Tests

There are a few types of non-invasive diagnostic tests that can identify the effects of demyelination on the peripheral nerves or optic nerves.

Electromyography (EMG): An EMG study is done as part of a neuropathy evaluation. This test measures the muscle response to nerve stimulation. This examination is slightly uncomfortable, but it is safe, and any discomfort resolves once the test is completed.

Nerve conduction studies (NCV): NCV studies, like EMGs, are done to evaluate peripheral neuropathy. This test measures how fast the nerves conduct electrical signals. It involves direct stimulation of the nerve by shock-emitting electrodes that are placed on the skin directly over the nerve. An NCV examination can be slightly uncomfortable, but it is safe and the discomfort does not persist after the examination is completed.

Evoked potentials: Evoked potential tests measure the response of the brain to certain stimuli. Visual evoked potentials, for example, measure the brain’s response to lights and other visual stimuli, and it is often used to help assess optic neuritis.

Lumbar puncture (LP): An LP, also often referred to as a spinal tap, is a test that allows your medical team to assess your cerebrospinal fluid (CSF). The fluid often shows signs of infection or inflammatory disease, and the results can be used to assist in the diagnosis of demyelinating conditions.

A physician will perform an LP by cleaning an area on your lower back, inserting a needle, and collecting spinal fluid. The test takes about 10 to 20 minutes and may be slightly uncomfortable.

Demyelinating Diseases

There are a number of different demyelinating diseases. Some affect the peripheral nerves, some affect the brain and/or spinal cord, and some affect both.

Demyelinating Disorders of the Brain and Spinal Cord

MS: MS is the most common demyelinating disease. It is characterized by demyelination in the brain, spine, and/or optic nerve. There are several types of MS, and some are characterized by relapses and remissions, while others are characterized by a gradual decline.

MS is diagnosed by physical examination, imaging studies, LP, and sometimes with evoked potential tests. MS usually starts between the ages of 20 and 40, and, while it is manageable, it is a lifelong illness with no definitive cure.

Clinically isolated syndrome (CIS): CIS is a single episode that has all the characteristics of MS. Sometimes, CIS turns out to be the first episode of a relapsing form of MS, but often it does not ever occur again. It is diagnosed in the same way MS is diagnosed.

Acute disseminated encephalomyelitis (ADEM): A rapidly progressive demyelinating episode, ADEM often affects young children. The symptoms are usually more intense than those of MS, and the condition typically resolves without lasting effects or a recurrence.

CALD: A severe genetic condition that affects young boys (because it is an X-linked recessive disorder), CALD causes vision loss and profound loss of muscle control. The demyelination results from a defect in fatty acid metabolism that results in the destruction of myelin in early childhood. This condition is not treatable and results in early death. A milder variant, adrenomyeloneuropathy (AMN), is caused by the same gene. AMN predominantly affects young men, causing progressive weakness, and may result in wheelchair dependence, but is not fatal.

Progressive multifocal leuokoencephalopathy (PML): This is a severe demyelinating disease that occurs due to reactivation of a virus (JC virus). Most people have been exposed to this virus, which can cause a mild cold.

Reactivation tends to occur among people who have severe immune deficiency, and it causes extensive brain involvement, often with permanent neurocognitive impairment. PML is often diagnosed based on the medical history, imaging tests, and by demonstrating the presence of the JC virus in the spinal fluid. Sometimes a brain biopsy is needed.

Demyelinating Disorders of Peripheral Nerves

Hereditary demyelinating neuropathies: This is a group of inherited neuropathies characterized by segmental demyelination of the peripheral nerves. An example is Charcot-Marie Polyneuropathy Type 1. Patients usually present with slowly progressive weakness and numbness, initially affecting the lower legs and then the hands. Wasting of muscles is seen frequently.

Guillain-Barre syndrome (GBS): A sudden, rapidly worsening illness, GBS causes weakness that begins in both feet, involving the legs and arms within a few days. GBS is a serious condition because it can cause weakness of the respiratory muscles that control breathing. Respiratory support with machine ventilation may be necessary.

The condition typically affects adults over age 50, and it is diagnosed based on clinical examination, and sometimes with EMG/NCV as well. GBS is typically treated with intravenous immunoglobulin (IVIG), a therapy that suppresses the immune system, or with plasma exchange, a procedure that filters the blood. With treatment, there is usually a good prognosis.

Chronic inflammatory demyelinating polyneuropathy (CIDP): This is a recurrent form of GBS characterized by episodes of weakness. Episodes are usually treated with IVIG or plasma exchange.

Other Causes

Hypoxia: A lack of oxygen, due to a cardiac arrest from a heart attack or depressed breathing from an overdose, generally causes necrosis of the brain. However, sometimes demyelination can also be seen. Recovery depends on the extent of the damage.

Vitamin B12 deficiency: Vitamin B12 has many functions in the body, including helping in myelin production. Deficiency of this vitamin causes demyelinating disease of the spine as well as peripheral neuropathy. A person who has vitamin B12 deficiency may experience one or more effects. 

Copper deficiency: Similar to B12 deficiency, low copper secondary to a prior history of gastric surgery, excessive intake of zinc, or malabsorption can affect the spinal cord and peripheral nerves.

A deficiency is unlikely to cause demyelination, but it may contribute to demyelinating disease.

Toxin exposure: Medications and toxin exposures can temporarily damage myelin, or may cause long-term damage. It can be very difficult to pinpoint the exact cause of toxin-induced demyelination. Once the offending agent is identified, reducing exposure is the key to recovery.

Treatment

The treatment of demyelination depends on the condition. Treatment is focused on management of symptoms and preventing further demyelination. At the current time, there is no treatment that effectively restores or rebuilds myelin, but typically, myelin regularly regenerates on its own. If there is little or no nerve damage, symptoms can resolve and neurological recovery is possible.

There are a number of treatments used to prevent demyelination.

Immunosuppression

Preventing the inflammatory process is central to the treatment of many demyelinating conditions, such as MS, CIS, ADEM, GBS, and CIDP. Many of these conditions are treated with a brief course of intravenous (IV) steroids or plasma exchange.

Because MS is chronic, the disease is managed with MS disease-modifying therapy (DMT). Steroids and DMTs work by suppressing the immune system to prevent the inflammatory attack on the myelin. 

Avoiding Toxins

Stopping toxin exposure will likely not reverse your symptoms, but can help prevent further neurological damage.

Supplements

Because some nutritional deficiencies, such as B12 and copper, have been associated with demyelination, restoration of normal nutrient levels can be an important treatment strategy.

Symptomatic Treatment

If you have a demyelinating condition, you may need to have treatment for your specific symptoms. For example, you may need to take medication to help control your pain or discomfort. Medication can also help control symptoms such as anxiety or depression. For some people, bladder dysfunction can improve with medication.

Rehabilitation

Often, rehabilitation is the key to recovery. Physical therapy, speech or swallow therapy, and balance therapy are examples of the types of rehabilitation that can help you as you recover from or cope with your demyelinating illness.

A Word From Verywell

Demyelination can result from a number of different causes and there is a range of demyelinating diseases, each with its own typical age group, symptoms, cause, treatment, and prognosis.

If you or a loved one has been diagnosed with demyelination, you should rest assured that most of the time, demyelination is a manageable condition.

 

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