Demyelination refers to the loss or damage of myelin in the nervous system. Myelin plays an important role in the transmission of neural signals as it electrically isolates the nerve fibers (axons). For this reason, demyelination without treatment leads to a variety of long-term impairments; however, the prognoses differ for different underlying causes.
Demyelination is the loss or damage of myelin in the nervous system. Illustration shows neuron with myelin sheath.
Demyelination is also known as demyelination and can affect both the central and peripheral nervous systems. Myelin is a biological membrane that contains numerous lipids. Different cells in the body can produce myelin, for example Schwann cells or cells of the peripheral and central nervous system.
The name myelin is derived from the Greek word for marrow or brain ("myelòs"). Since myelin reflects light well, it looks white when viewed microscopically. This is where the term “white matter” comes from, which describes a certain type of neuronal tissue: This tissue consists primarily of nerve cells whose nerve fibers (axons) are surrounded by myelin.
Myelin is of great importance for the proper functioning of the human nervous system.
As an insulating cover, it surrounds the axons of the nerve cells and thereby promotes the transmission of electrical impulses. The electrical isolation increases the speed of the transmission and increases the reliability of the signal transmission. The disturbed neural communication therefore leads to rather diffuse complaints. Examples are fatigue, motor disorders, weakness and visual disturbances.
Demyelination is a pathological damage or loss of the myelin. It occurs primarily in the context of a demyelinating disease such as multiple sclerosis.
Another possible reason for demyelination is direct impairment of the nerve cells; Medicine speaks of primary neuronal damage in this form of demyelinating. In these cases, defects in the cell bodies or axons lead to the destruction of the myelin. However, the effects on signal transmission are largely the same for both variants.
In addition, in almost all forms of demyelination, medical professionals assume an influence of individual lifestyle. Diet, smoking and obesity are just a few of the factors that may play a role in this context.
Depending on the spatial distribution of the affected nerve cells, experts speak of diffuse or focal demyelination. In focal demyelination, the demarcated nerve cells are in close proximity to one another and form hotspots. Several such stoves are also possible. As demyelinating diseases progress, the foci gradually expand as the disease increasingly damages new nerve cells. In contrast to focal demyelination, the diffuse variant does not form any contiguous areas of demarcated nerve cells: In this case, the damage to the myelin does not follow a known pattern.
Diseases that are associated with demyelination can be a consequence of inflammatory and degenerative processes. The degenerative-metabolic demyelinating of the myelin sheath occurs, for example, after damage to the brain, which can manifest itself after infections and (in rarer cases) vaccinations.
In the majority of cases, however, demyelinating diseases are primarily diseases such as multiple sclerosis. This form of nervous degeneration leads to the destruction of the myelin sheaths, which electrically isolate the axons of the nerve cells. The cells of the central nervous system, i.e. the brain and the spinal cord, are affected. Multiple sclerosis is a progressive, chronic inflammatory disease, the exact origins of which are still unknown. Possible causes include inflammation, impaired metabolism, infections, nutrition, poisoning and various defective functions within the immune system. Multiple sclerosis progresses in flares, between which the disease can temporarily stabilize.
Another demyelinating disease is leukoencephalitis. Leukoencephalitis is a form of encephalitis that affects the white matter of the brain and gradually reduces it. Besides polioencephalitis (inflammation of the gray matter), leukoencephalitis is a variant of panencephalitis.
Another disease that leads to demyelination is neuromyelitis optica (NMO) or Devic's syndrome. Demyelination in NMO occurs in the form of a focal point. Recurring inflammation of the optic nerve and prolonged inflammation of the spinal cord (myelitis) are the most critical risk factors for NMO. Visual disturbances, weakness, paralysis and disorders of the bladder function can appear as signs of NMO, along with other symptoms. Permanent damage caused by NMO is possible, although the treatment often achieves good results and can prevent long-term impairment.
While inflammation causes demyelination in multiple sclerosis and leukoencephalitis, a metabolic disorder is responsible for the breakdown of myelin in leukodystrophy. Various underlying metabolic diseases can be considered as triggers, which in turn usually have genetic causes. Leukodystrophy also leads to rather diffuse symptoms.
A demyelinating disease that can be noticed in newborns and young children is Alexander disease. The brains of the affected children show an insufficient mass of myelin membranes early on. As a result, in addition to the usual motor symptoms, there are also noticeable developmental delays in comparison with children of the same age.
But Alexander's disease can also manifest itself for the first time in adulthood. The disease is progressive and incurable at any age. The cause of Alexander disease is a very rare genetic abnormality.