Myelin is a protective material that surrounds the nerve fibers located in the brain and spinal cord. Any condition that results in damage or deterioration of myelin is known as a demyelinating disease. When this tissue, also known as the myelin sheath, is damaged, the nerve impulses that travel throughout the body slow and may even come to a stop, resulting in significant neurological problems. There are a number of common demyelinating diseases, including multiple sclerosis (MS), which present significant issues for affected individuals.
Definition & Facts
The nerves in the body are responsible for sending messages throughout every part of the body and then decoding those messages in the brain. The nerves facilitate an individual’s capacity to speak, feel, see, and even think. Nerves are protected by myelin, which is a membrane layer of an axon. This coating facilitates faster transmission of those nerve impulses throughout the body. However, certain diseases cause damage to the myelin. Depending on the demyelinating disease, an individual may develop a wide range of symptoms related to sensation, moving, hearing, seeing, and thinking clearly and effectively.
Examples of demyelinating diseases include the following: optic neuritis, transverse myelitis, acute disseminated encephalomyelitis, neuromyelitis optica, central pontine myelinolysis, extrapontine myelinolysis, acute haemorrhagic leukoencephalitis, and progressive multifocal leukoencephalopathy.
Two different types or categories of demyelinating diseases are inflammatory demyelination and viral demyelination. Inflammatory demyelination occurs as the body’s immune system attacks itself and targets the myelin. Multiple sclerosis, optic neuritis, and acute disseminated encephalomyelitis (ADEM) are common types of inflammatory demyelination caused by inflammation located in the brain and spinal cord. Guillain-Barré syndrome (GBS) is a condition that involves inflammation of the peripheral nerves in the body.
Viral demyelination occurs when a virus attacks the myelin coating, such as with progressive multifocal leukoencephalopathy (PML). Alcoholism, chronic liver disease, and electrolyte imbalances may also contribute to myelin damage. Additionally, demyelination can occur as a result of lack of oxygen (hypoxia) or other cardiovascular disease affecting the brain.
Symptoms & Complaints
Even so, there are a number of common signs and symptoms of demyelinating disease that may be at play. Symptoms of this type of disease may affect any of the body’s capabilities or systems within the body, including visual, motor, and sensory capacity as well as cerebellar, genitourinary, and neuropsychiatric functions. Some of the most common symptoms of this type of disease include:
- Blurred vision
- Vision loss or blindness
- Weakness and limb weakness
- Difficulties with balance
- Loss of coordination
- Loss of bladder control (urinary incontinence) and/or loss of bowel control (fecal incontinence)
- Memory loss and cognitive impairment
Not everyone is affected by this type of disease in the same way. However, many early signs of the condition are relatively common across the spectrum of the condition. Early detection is one of the best defenses against the disease. A common early symptom of this type of disease, in addition to many of the symptoms that are listed above, is nerve pain.
The cause of demyelination depends on the disorder. In many causes of inflammatory demyelination, it is unclear what triggers the autoimmune response in the first place. Multiple sclerosis (MS) is the most prevalent demyelinating disease, which affects the central nervous system. This disorder is caused by the immune system attacking the myelin sheath. This process causes inflammation and damage to the sheath as well as the nerve fibers that it surrounds. The common result is areas of scarring or sclerosis.
Optic neuritis is caused by inflammation of the optic nerve in one or both eyes. Neuromyelitis optica is known for inflammation and breakdown of the myelin in the central nervous, specifically the spinal cord and optic nerve. Inflammation of the spinal cord causes transverse myelitis while inflammation of the brain and spinal cord is known as acute disseminated encephalomyelitis.
Some demyelinating diseases have causes that have been confirmed. Adrenoleukodystrophy and adrenomyeloneuropathy are rare, genetic disorders caused by genetic mutations in the ABCD1 gene which produces ADLP, a protein that breaks down very long chain fatty acids. Because the mutation results in less ADLP, more VLCFAs proliferate than is healthy to the body, and their toxic presence trigger the immune system to attack myelin.
Certain infections can cause demyelination. Progressive multifocal leukoencephalopathy is caused by a papovavirus. Though its causes have not been fully understood or confirmed, transverse myelitis is linked to viral infections like shingles and chickenpox. Central pontine myelinolysis is caused in many cases by alcoholic liver disease.
Diagnosis & Tests
Diagnosis of demyelinating disease will involve establishing the patient's family history, medical history, and presentation of symptoms. Neurological examinations, eye examinations, and hearing tests will all play their part in establishing the severity of symptoms. An electroencephalogram may be performed to establish how the brain responds to stimuli (its evoked potential).
Diagnosis of demyelinated diseases is aided by medical imaging tests such as magnetic resonance imaging (MRI) scans. MRI's may reveal lesions in the brain and spinal cord and may reveal abnormalities of the grey matter and white matter of the brain which can indicate demyelination.
Blood tests are also useful, particularly in diagnosing demyelinating diseases caused by viral infections. Polymerase chain reaction tests can show the presence of certain viral acids. Tests of the cerebrospinal fluid via a lumbar puncture (or spinal tap) are useful in the diagnostic process.
Treatment & Therapy
There are currently few cures for demyelinating diseases, and the symptoms and complaints are often different for everyone. Treatment is typically focused on minimizing the effects of the attacks, modifying the pathology and development of the disease, and managing the symptoms.
Several drug therapies are currently recommended for treatment depending on the individual’s specific disorder. Common treatments include medications that are designed to decrease the frequency of new lesion formation. Many treatments are also designed to reduce the immune response within the body, including drugs such as interferon beta-1a or glatiramer acetate.
It has also been noted that individuals with low levels of vitamin D more commonly develop MS and other demyelinating diseases, so increasing vitamin D in the body may reduce inflammatory immune responses.
Therapies designed to treat the common symptoms of these conditions include physical therapy, occupational therapy, muscle relaxing drugs, and medications to reduce fatigue and reduce pain (painkillers). It is important to work with one's doctor to identify a specific course of action that is the best treatment for one's individual case.
Prevention & Prophylaxis
Practices such as increasing one’s intake of vitamin D may reduce inflammation within the body and delay onset of the condition. Taking fish oil or other fatty acid supplements may also support the health of the brain and surrounding tissue and reduce one’s risk of a number of different conditions. Adding alpha lipoic acid supplements may also be beneficial to the nervous system and offset the development of demyelinating diseases.