An Overview of Demyelination

When the Protective Layer That Surrounds Nerves Is Impaired

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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 condition is multiple sclerosis (MS). 

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

This article explains the symptoms and causes of demyelination and the non-invasive tests that physicians use to form a diagnosis. It also describes some common demyelinating disorders of the brain and spinal cord and the peripheral nerves.

Demyelination

Verywell / Jiaqi Zhou

Symptoms

Demyelination can occur at any age, but each demyelinating condition tends to affect certain age groups. The symptoms of demyelination correspond to the affected area of the nervous system. 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. It may also diminish bowel and bladder control. Demyelination in the brain can cause a variety of problems, such as impaired memory or decreased vision. Common symptoms of demyelinating diseases include:

  • Bladder and/or bowel issues
  • Chewing or swallowing difficulties
  • Concentration lapses
  • Coordination loss
  • Fatigue
  • Impaired memory
  • Loss of or diminished vision
  • Mood or behavioral changes
  • Numbness or tingling in the hands, feet, arms, legs, or face 
  • Slurred speech
  • Walking difficulties
  • Weakness in the arms or legs

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. In fact, they can be fatal.

Recap


The symptoms of demyelination correspond to the affected area of the nervous system. The symptoms of demyelination may come and go. Or they may gradually worsen.

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 harm myelin or interfere with its production. A lack of myelin formation can also follow 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 they can occur without a clear trigger. GBS is rapid-onset muscle weakness.

Recap

Demyelination is often caused by inflammation, which attacks and destroys myelin. This is a type of fatty tissue that surrounds and protects nerves throughout the body.

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 as well as to identify the specific triggering illness.

Clinical Examination

When you are being evaluated for a demyelinating illness, your healthcare provider may:

  • Record your medical history and ask questions about how long you've had your symptoms, whether you've experienced them before, and whether you've been sick with an infection.
  • 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 in general.
  • Check your muscle strength, sensation, coordination, and ability to walk. Your healthcare provider may check your vision and how your pupils react to light. You might have an ophthalmologic examination in which your healthcare provider 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

Several non-invasive diagnostic tests 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.

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. They often 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. The test takes about 10 to 20 minutes and may be slightly uncomfortable.

Nerve conduction studies (NCV): Studies of this type, 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 stops after the examination is over.

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 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 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. While it is manageable, it is a lifelong illness with no definitive cure.

Clinically isolated syndrome (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 then it often does not occur again. It is diagnosed in the same way as MS.

Acute disseminated encephalomyelitis (ADEM) is 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 is a severe genetic condition that affects young boys (because it is an X-linked recessive disorder). CALD causes vision loss and a 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. It may cause wheelchair dependence, but it 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 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 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 (atrophy) of muscles is common.

Guillain-Barre syndrome (GBS) is 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. It is diagnosed based on clinical examination, and sometimes with EMG/NCV. 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. Either way, there is usually a good prognosis.

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

Other Causes

Hypoxia: This lack of oxygen, due to a cardiac arrest from a heart attack or depressed breathing from an overdose, generally causes necrosis of the brain. Recovery depends on the extent of the damage.

Vitamin B12 deficiency: The vitamin 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.

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.

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.

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

Treatment

The treatment of demyelination depends on the condition. Treatment is focused on management of symptoms and preventing further demyelination. At present, there is no treatment that can restore or rebuild myelin. Typically, myelin regenerates on its own. If there is little or no nerve damage, symptoms can resolve and neurological recovery is possible.

Some tactics that can prevent demyelination include:

  • Immunosuppression, or blocking the pathways that lead to inflammation. For example, since multiple sclerosis is chronic, it is managed with MS disease-modifying therapy (DMT). Steroids and DMTs work by suppressing the immune system to prevent an inflammatory attack on the myelin. 
  • Supplements, which can restore nutritional deficiencies. For example, a lack of vitamin B12 and copper have been linked to demyelination, so they can play an important role in treatment.
  • Symptomatic treatment, which is tailored to a specific symptoms. For example, some people need medication to ease pain or discomfort. Medication can also help control symptoms such as anxiety or depression. For other people, bladder dysfunction can improve with medication.
  • Rehabilitation, which can include physical therapy, speech or swallow therapy, and balance therapy, are examples of the types of rehabilitation that can help someone recover from or cope with a demyelinating illness.
  • Avoiding toxins, which probably won't reverse symptoms but can prevent further neurological damage.

Summary

Demyelination occurs when there is a loss of myelin, a type of fatty tissue that surrounds and protects nerves throughout the body. 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. A lack of myelin formation can also follow some nutritional deficiencies. The symptoms of demyelination correspond to the affected area of the nervous system. For example, peripheral neuropathy affects the hands and feet in what is often described as a “stocking glove” distribution. There are several risk factors for demyelination, including genetics, infections, toxicity, and nutritional deficits. The treatment of demyelination depends on the condition.

A Word From Verywell

No cure exists for demyelination or multiple sclerosis, but you can manage the symptoms. Assembling the right treatment team can make a huge difference. Check with your primary care physician about, say, adding a neurologist, registered dietician or nutritionist, a physical therapist, and a home caregiver to your inner circle. You may have to put your heads together and make some compromises, but specialists can buoy a patient's care and improve their quality of life.

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10 Sources
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