Demyelinating Diseases: A useful guide to diseases involving myelin
What are the types of demyelinating diseases that affect the central nervous system? In this article, we answer all your questions: functions of myelin, causes of demyelination, general symptoms of demyelination, demyelination, and the brain, demyelinating diseases (multiple sclerosis, optic neuromyelitis, acute disseminated encephalitis) and treatments for demyelinating diseases.
What is a demyelinating disease?-Concepts and definition
A demyelinating disease is any condition that causes damage to the protective lining (myelin sheath) that envelops the nerve fibers of our brain, spinal cord, or optic nerves.
When the myelin sheath is damaged or deteriorated, nerve impulses decrease or even stop, causing neurological problems, deficits in sensory-motor and cognitive processes.
Myelin is a layer of fat located in the nerve cells in the axons, between each myelin segment there are interrupting nodes known as Ranvier’s nodes (Kandel, Jessell and Schwartz, 2003).
It is at these nodes that the transmission of electrical messages takes place, and this process is known as salting conduction (Purves et al., 2008).
The molecular composition of myelin is 80% lipid or fat and 20% protein. In addition, physiologically, myelin is several laminated segments of different lengths ranging from 1mm to 1.2 um (Carlson, 2006).
How is myelin produced in our body? Myelin is produced in the central nervous system by oligodendrocytes, a type of glial cell. This cell deposits different layers of myelin in some axons of the nervous system. When myelin production is in the peripheral nervous system, the cell that generates myelin is known as Schwan’s cell (Purves et al., 2008).
Thus, demyelination can be defined as the rupture process of myelin caused by various causes (infectious, genetic causes, etc.), which prevents the myelin from performing its functions properly.
Shi et al. define demyelination as the loss of myelin sheeting, which produces white substance involvement causing deficits in both sensory-motor and cognitive processes.
Demyelination is one of the most studied neurodegenerative processes due to its great linkage in pathologies such as multiple sclerosis.
Demyelinating Disease-Functions of myelin
Myelin has great importance in the nervous system, its main functions are:
- Myelin prevents transmission of adjacent neurons (Carlson, 2006)
- Myelin increases the transmission rate of electrical signals from neurons (Purves et al., 2008)
- Myelin covers a part of the axon which produces electrical isolation (Akkermann, Jadasz, Azin and Küro, 2016)
- Myelin provides metabolic and supplements such as lactose and promotes the growth of dendritic spines.
Demyelinating Diseases- Causes of demyelination
There are several factors that cause demyelination and these factors are divided into three main groups:
According to the animal models, which state that myelin is swollen and this c the uses destruction of it (Kandel et al., 2004). However, in humans, the inflammation of myelin sheaths is caused by activation of the immune response (Domínguez and Guzmán de Villoria, 2010).
At a genetic level, in demyelinating processes, it has been shown that mutations in certain dominant autosomal genes, and in recessive autosomal X-linked genes, produce demyelinating diseases. However, the incidence of these mutations is 0.0004 (Lara-Aguilar et al., 2012).
Demilinization can be caused by metabolic problems, since, the deterioration in the mitochondria of the cell produces more atrocities and worsen production of oligodendrocytes.
Demyelinating Diseases- Symptoms of demyelination
Demyelination presents different general symptoms, which are grouped into three large groups:
1. Symptoms related to motor impairment
As for motor alterations and demyelination, symptoms are observed that hinder gait, reduction in the length of the walk, loss of muscle tone and elasticity (Shahraki et al., 2017). In addition, demyelinating processes can produce motor incoordination (Kandel et al., 2004) that can affect cerebellar structures (Shahraky et al., 2017).
Nevertheless, it has been proven that stimulation through music is positive in this type of patients (Sharaky et al., 2017). Therefore, despite the motor alterations that these pathologies produce, there may be a slight hope of rehabilitating and compensating a certain degree of motor function, although it is difficult to achieve all motor function.
2. Symptoms related to perceptual disturbances
Demyelinating diseases can present perceptual alterations (Kandel et al. 2004). Although, in pathologies such as multiple sclerosis, it is not frequent to present perceptive symptoms such as spatial and visual agnosia (Moreno et al., 2013).
3. Symptoms related to cognitive impairment
Cognitive alterations in demyelinating diseases are varied and very limiting, as in the case of multiple sclerosis, since between 40% and 65% of people suffering from the benign version of this demilienizing disease have cognitive rigidity. In addition, 38% of benign multiple sclerosis patients suffer from bradypsychia or slowing down of processing speed, which reduces their freedom in the activities of daily life (Ton, Vasconcelos, and Alvarenga, 2017).
Other cognitive deficits linked to demilitarizing diseases are aphasia, apraxia, and alterations of consciousness, as well as other pathologies, attention deficit, abstract reasoning, verbal fluency and visuospatial alterations (Ton and cols., 2017), the latter being the last processes that compose the superior psychological process called executive functions. In Gil et al. (2013) claim deficits in memory.
Demyelinating disease- Demyelination and brain
Demyelinating processes cause cognitive, perceptual and motor alterations, however, at the neurological level the destruction of myelin affects the processing of the neurological message, leading to a reduction of cortical volume, deterioration in cerebral areas (internal capsid, brain stem, and spinal cord) (Ton and cols., 2017). Also, white matter (Gil et al., 2013) is affected, similar to the brain of the elderly person.
Although it is true that deterioration in the white matter and neurological substance does occur, the brain tries to compensate or restore neurological deterioration (Ton and cols., 2017).
Thus, we can affirm that myelin is a component of neurological wiring, which favors the transmission of the neural message. And when it is affected by demyelination processes, there is a slowdown in processing speed, which ultimately affects several cognitive domains (memory, attention, language, apraxia, executive functions among others) and different brain areas, both subcortical and cortical structures, which are mentioned above.
Therefore, the deterioration of brain structures, according to the author’s opinion, can be defined as deterioration, which is largely variable and progressive, as well as not very focused, in contrast to traumatic brain injury.
There are numerous syndromes derived from different demyelinating diseases.
1- Multiple sclerosis
Multiple sclerosis is a neurodegenerative and chronic disease that affects the central nervous system. It has an inflammatory and demyelinating origin, whose clinical course is heterogeneous, and in most patients gradual and progressive (Ton and cols., 2017). This disease causes axonal degeneration and is considered part of autoimmune diseases (Gil et al., 2013).
Furthermore, we can affirm that multiple sclerosis presents genetic vulnerability factors, that is, the presence of the HLA-RR2 and HLA-DQ genes facilitate the appearance of the disease (Hervas-Garcia, Diaz-Otero, and Amosa-Delgado, 2017).
2- Optical neuromyelitis
Optical neuromyelitis is considered a demyelinating disease, characterized by the presence of aquaporin-4 antibody (Hervas-Garcia et al., 2017). In addition, it is a pathology that is defined as an autoimmune disease with great functional impairment, which can cause cortical blindness and is more limiting than multiple sclerosis (Domínguez and Guzmán de Villoria, 2010).
However, the etiology of this pathology is diverse, therefore, it is not possible to clarify a clear cause of why the demyelinating is happening.
3- Acute disseminated encephalitis
Acute disseminated encephalitis is a disease of variable etiology that can cause seizures and disturbances of consciousness (García-Mocón, 2010). The demyelinating causes of this pathology can be caused, classically, by viruses or vaccines, having a higher prevalence in children, but being rare (Domínguez and Guzmán de Villoria, 2010).
The most interesting thing about disseminated acute encephalitis is that one of the viruses causing its symptoms is the chickenpox virus. (García-Mocón, 2010).
Treatment for demyelinating diseases
There is currently no cure for demyelinating diseases and their progression. The symptoms of these diseases are different for each individual. It is important to detect and approach treatment of the disease at early stages.
Treatment for demyelinating diseases focuses on the following points:
- Minimize the effects of attacks
- Changing the course of the disease
- Managing symptoms
The professional diagnosing the disease may recommend various medications depending on the particular disorder and symptoms of the patient. Strategies for treating symptoms include physical therapy, cognitive stimulation, muscle relaxants and medications to reduce pain and combat fatigue, etc.
If you have any questions, you can leave it below. We will be happy to help you in any way we can.
This article is originally in Spanish by Alba Yela, translated by Alejandra Salazar.
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Alejandra is a clinical and health psychologist. She is a child specialist with a diploma in evaluation and intervention in autism. She has worked in different schools with young children and private practice for over 6 years. She is interested in early childhood intervention, emotional intelligence, and attachment styles. As a brain and human behavior enthusiast, she is more than happy to answer your questions and share her experience.