Demyelinating polyneuropathies: what are they, types, symptoms and treatment?

This type of disease affects the myelin that covers the fibers of the peripheral nervous system.

Demyelinating polyneuropathies are a group of disorders that affect the nervous system and produce alterations in motor functions. and produce alterations in motor and sensory functions. Their main characteristic is the loss of myelin that occurs in the nerve cells and is responsible for the problems that these patients present.

Below, we explain what they consist of and what are the characteristics of this type of disorders, how they are diagnosed, what are the main types that exist and the current treatment available.

Demyelinating polyneuropathy: definition and characteristics.

Demyelinating polyneuropathies are a group of neurological diseases, which can be hereditary and acquired, characterized by damage to the myelin of the nerve fibers of the peripheral nervous system.. Generally, this type of disorder is associated with decreased or loss of muscle strength and/or sensory loss.

Demyelination is a process involving loss of or damage to the myelin sheath covering the axons of nerve cells. The main function of myelin is to increase the speed of transmission of nerve impulses, so it is essential for the proper functioning of the nervous system activity.

Pathologies that involve demyelination usually affect basic functions and have a significant impact on patients' lives. The alterations can range from muscular or sensory problems to cognitive and functional impairment that can permanently and absolutely disable the person.

Diagnosis

Demyelinating disorders affecting the peripheral nerves are usually diagnosed based on the observation of symptoms and signs, following electromyographic tests (which evaluate the state of the muscles and nerves), genetic studies and sometimes data collected from nerve biopsy.

In order to correctly diagnose a demyelinating polyneuropathy, demyelinating polyneuropathy must be differentiated from other types of polyneuropathies and disorders that also affect the peripheral nervous system (such as mononeuropathies). (such as mononeuropathies, radiculopathies, etc.), and the mechanism that has caused the damage (demyelinating or axonal) must be established, as well as the cause of the disease.

During data collection and diagnosis, other relevant aspects should be considered, such as: the modality of involvement (predominantly sensitive, motor, etc.), the types of fibers affected (coarse or fine), the temporal profile (acute, subacute or chronic), the evolutionary profile (monophasic, progressive or relapsing), the age of onset, presence or absence of toxic substances, family history and the existence of other concurrent disorders.

Types

There are multiple variants of demyelinating polyneuropathies and their most common classification is based on a criterion of origin; that is, whether they are hereditary or acquired. Let us see what they are:

1. Hereditary

Hereditary demyelinating polyneuropathies are associated with specific genetic defects. are associated with specific genetic defectsThe mechanisms by which these mutations cause the pathological manifestations of demyelination are still unknown.

There are many hereditary variants of this disorder. Here we will review three of them: Charcot-Marie-Tooth disease, Refsum disease and metachromatic leukodystrophy. Let us look at their main characteristics and clinical manifestations.

1.1. Charcot-Marie-Tooth disease

There are more than 90 variants of this hereditary polyneuropathy and each type is caused by different genetic mutations. Charcot-Marie-Tooth disease affects all individuals, races and ethnic groups equally, and is suffered by about 2.8 million people worldwide.

In the most common types, symptoms usually begin in the early 20s and may include: foot deformity, inability to hold the foot horizontally, feet often strike the ground when walking, muscle loss between the legs, numbness of the feet, and balance problems. Similar symptoms may also appear in the arms and hands, and the disease rarely affects function. the disease rarely affects brain function..

1.2. Refsum disease

Refsum disease is an inherited sensory-motor neuropathy characterized by the accumulation of phytanic acid. It is prevalent in 1 person per million and affects males and females equally. Initial symptoms usually originate around 15 years of age, although they can also appear during childhood or in adulthood (between 30 and 40 years of age).

The accumulation of phytanic acid causes patients to have lesions in the retina, brain and peripheral nervous system. In most cases, the cause of this disorder is a mutation in the PHYN gene, although recent studies have found that another possible mutation, in the PEX7 gene, could also be a causative factor.

1.3. Metachromatic leukodystrophy

Metachromatic leukodystrophy is a neurodegenerative disease characterized by the accumulation of sulfatides in the accumulation of sulfatides in the central nervous system and kidneys.. There are three types: late infantile, juvenile and adult. The prevalence of this disorder is estimated to be about 1 case in 625,000 people.

The late infantile form is the most common and usually begins at ages when children are learning to walk, with symptoms such as hypotonia, gait difficulties, optic atrophy and motor regression preceding cognitive impairment. The peripheral nervous system of these patients is systematically damaged (drastically decreases the speed of nerve conduction).

2. Acquired

Acquired demyelinating polyneuropathies of acquired type represent a heterogeneous group, with a multitude of types and variants.. These diseases can have different causes: toxic (such as heavy metals), deficiencies (of vitamin B12, for example), metabolic, inflammatory or infectious, immune, among others.

Chronic inflammatory demyelinating polyneuropathy (CIDP) is one of the most common forms of this type of polyneuropathy, and one of its best known variants is Guillain-Barré disease or syndrome.

The main characteristics and clinical manifestations are described below.

2.1. Chronic inflammatory demyelinating polyneuropathy (CIDP)

CIDP is, as mentioned, one of the most common forms of acquired polyneuropathies. It has an insidious onset and usually progresses for at least 2 months.. Its course can be recurrent or chronically progressive, and it is usually motor predominant, affecting proximal and distal muscle groups.

This disease has an incidence of 0.56 cases per 100,000 people. The average age of onset of the disorder is around 47 years, although it affects all age groups. The clinical manifestations of this polyneuropathy include proximal muscle weakness and distal sensory loss in the extremities that are progressive and symmetrical.

In addition, this disease is often accompanied by a decrease or, sometimes, total loss of osteotendinous reflexes.. Although there are variants with purely motor involvement, these are the least frequent (around 10% of cases). Cranial nerves are not usually affected and a common symptom is bilateral facial nerve paresis. Rarely, respiratory capacity and urination are also affected.

2.2. Guillain-Barré syndrome

Guillain-Barré syndrome, also known as acute idiopathic polyneuropathy, is a disorder that causes inflammation of the peripheral nerves. It is characterized by an sudden onset of muscle weakness and often paralysis of the legs, arms, respiratory muscles and face.. This weakness is often accompanied by abnormal sensations and loss of the patellar reflex.

The disease can manifest itself at any age and in people of all ethnicities and locations. Although the causes of this disease are unknown, in half of the cases it occurs after a viral or bacterial infection. Current research suggests that there may be an autoimmune mechanism responsible for the demyelination process that characterizes this disorder.

Treatment

The treatment indicated varies according to the type of demyelinating polyneuropathy varies according to the type of demyelinating polyneuropathy and its symptoms and clinical manifestations.. In the case of CIDP, treatment usually includes corticosteroids such as prednisone, which may be prescribed alone or in combination with immunosuppressive drugs.

There are also other effective therapeutic methods, such as plasmapheresis or plasma exchange, a method by which Blood is removed from the patient's body and the white blood cells, red blood cells and platelets are processed, separated from the rest of the plasma, and then reintroduced into the blood; and intravenous immunoglobulin therapy, which is often used to treat diseases that cause immunodeficiency, and also in immunomodulatory therapies.

On the other hand, physiotherapy can also be useful in patients suffering from neuropathies. in patients suffering from demyelinating neuropathies, as it can improve muscle strength, function and mobility, as well as minimize the muscle, tendon and joint problems that such patients often suffer from.

Bibliographic references:

• Ardila, A., & Rosselli, M. (2007). Clinical Neuropsychology. Editorial El Manual Moderno.
• González-Quevedo, A. (1999). Chronic inflammatory demyelinating demyelinating polyneuropathy: a contribution to disease characterization. Rev Neurol, 28(8), 772 - 778.