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

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

Next, 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.

• Related article: "Myelin: definition, functions and characteristics"

Demyelinating polyneuropathy: definition and characteristics

Demyelinating polyneuropathies are a group of neurological diseases, which can be hereditary and acquired, characterized by causing damage to the myelin of the nerve fibers of the Peripheral Nervous System. Generally, this type of disorder occurs with decreased or loss of muscle strength and/or sensory loss.

Demyelination is a process that involves loss or damage to the myelin sheath that covers the axons of nerve cells. The main function of myelin is to increase the speed of transmission of nerve impulses, which is why it is essential for the activity of the nervous system to function correctly.

Pathologies that occur with demyelination usually affect basic functions and have a significant impact on the lives of patients. The alterations can range from muscular or sensory problems, to cognitive and functional deterioration that can permanently and completely disable the person.

Diagnosis

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

In order to correctly diagnose a demyelinating polyneuropathy, this disease must be differentiated from other types of polyneuropathies and disorders that also affect the peripheral nervous system (such as mononeuropathies, radiculopathies, etc.), and the mechanism that 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 type of involvement (predominantly sensory, motor, etc.), the types of fibers affected (thick or fine), the temporal profile (acute, subacute or chronic), the evolutionary profile (monophasic, progressive, or relapsing), age of onset, presence or absence of toxins, family history, and existence of other disorders concurrent.

Guys

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

1. hereditary

Hereditary demyelinating polyneuropathies are associated with specific genetic defects, despite the fact that the mechanisms through 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's see what are its 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 people, races and ethnic groups equally, and around 2.8 million people suffer from it worldwide.

In the most common types, symptoms usually begin by age 20 and can include: foot deformity, inability to keep foot horizontally, feet often hit the ground when walking, muscle loss between the legs, numbness in the feet, and problems with balance. Similar symptoms may also appear in the arms and hands, and the disease rarely affects brain function.

1.2. Refsum's disease

Refsum's disease It is a hereditary sensory-motor neuropathy characterized by the accumulation of phytanic acid.. Its prevalence is 1 person per million, and it affects men and women equally. The initial symptoms usually originate around 15 years of age, although they can also appear during childhood or in adulthood (between 30 and 40 years).

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

1.3. metachromatic leukodystrophy

Metachromatic leukodystrophy is a neurodegenerative disease characterized by 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 at around 1 case in 625,000 people.

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

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2. acquired

Demyelinating polyneuropathies of the acquired type represent a heterogeneous group, with a multitude of types and variants. These diseases can have different causes: toxic (such as heavy metals), due to deficiencies (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 polyneuropathies, and one of its best-known variants is the disease or syndrome of Guillain barre.

Next, we will see what its main characteristics and clinical manifestations are.

2.1. Chronic Inflammatory Demyelinating Polyneuropathy (CIDP)

CIDP is, as we said, one of the most common forms of acquired polyneuropathies. It begins insidiously and usually progresses over at least 2 months.. Its course can be recurrent or chronically progressive, and is generally predominantly motor, affecting proximal and distal muscle groups.

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

Furthermore, this disease It usually presents with a decrease or, sometimes, the total loss of deep tendon reflexes. Although there are variants with purely motor involvement, they are the least frequent (around 10% of cases). The cranial nerves are usually not affected and a common symptom is usually bilateral facial nerve paresis. Infrequently, 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 a sudden onset of muscle weakness and often paralysis in the legs, arms, respiratory muscles, and face. This weakness is frequently accompanied by abnormal sensations and loss of the knee jerk.

The disease can manifest at any age and in people of all ethnicities and places. 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 indicated treatment varies depending on the type of demyelinating polyneuropathy and its symptoms and clinical manifestations. For 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 extracted from the patient's body and the white blood cells, red blood cells and platelets are processed, separating them from the rest of the plasma, and then reintroducing them into the blood; and intravenous immunoglobulin therapy, which is often used to treat diseases that cause immunodeficiency, and also in immunomodulatory therapies.

Besides, physical therapy may also be helpful in patients suffering from demyelinating neuropathies, as it can improve strength, function and mobility muscle, as well as minimizing the problems in muscles, tendons and joints that usually suffer from this type of patients.

Bibliographic references:

• Ardila, A., & Rosselli, M. (2007). clinical neuropsychology. Editorial The Modern Manual.
• González-Quevedo, A. (1999). Chronic inflammatory demyelinating polyneuropathy: a contribution to the characterization of the disease. Rev Neurol, 28(8), 772-778.