Demyelinating polyneuropathy is a group of disorders that affect the nervous system and produce alterations in motor and sensory functions. Its main feature is the loss of myelin which occurs in nerve cells and is responsible for the problems presented by these patients.
Here we explain what they are and what are the characteristics of this type of disorder, how they are diagnosed, what are the main types that exist and the treatments currently available.
Demyelinating polyneuropathy: definition and characteristics
Demyelinating polyneuropathy is a group of neurological diseases, which can be inherited and acquired, characterized by causing damage to the myelin nerve fibers of the peripheral nervous system. Usually these types of disorders occur with decrease or loss of muscle strength and / or loss of sensation.
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, so it is essential that the activity of the nervous system is functioning properly.
Pathologies that occur with demyelination often affect basic functions and have a significant impact on the lives of patients. The alterations can range from muscle or sensory problems to cognitive and functional disorders that can permanently and completely incapacitate the person.
Demyelinating disorders that affect peripheral nerves are usually diagnosed based on observing symptoms and signs, after performing electromyographic tests (which assess the condition of muscles and nerves), genetic studies, and sometimes data. . Collections of nerve biopsies.
In order to correctly diagnose demyelinating polyneuropathy, this disease must be differentiated from other types of polyneuropathy and disorders that also affect the peripheral nervous system (Like mononeuropathy, radiculopathy, etc.) and the mechanism that caused the damage (demyelinating or axonal) as well as the cause of the disease must be established.
During data collection and diagnosis, other relevant aspects should be taken into account such as: the type of affectation (predominantly sensitive, motor, etc.), the types of affected fibers (thick or thin), the temporal profile (acute, subacute, or chronic), evolutionary profile (single-phase, progressive or recurrent), age of onset, presence or absence of toxins, family history and existence of other concomitant disorders.
There are multiple variants of demyelinating polyneuropathy and its most common classification is based on a criterion of origin; that is, if they are of the hereditary or acquired type. Let’s see what they are:
Hereditary demyelinating polyneuropathy they are associated with specific genetic defectsAlthough the mechanisms by which these mutations cause the pathological manifestations of demyelination are still unknown.
There are many inherited variants of this disorder. We will review three here: 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 over 90 variants of this inherited polyneuropathy and each type is caused by different genetic mutations. Charcot-Marie-Tooth disease affects all people, races and ethnicities alike, and nearly 2.8 million people worldwide have it.
In the most common types, symptoms usually start at age 20 and can include: deformity of the foot, inability to keep the foot horizontal, feet typically hitting the ground when walking, muscle loss between the legs , numbness in the feet and problems with balance. Similar symptoms can also appear on the arms and hands, and the disease rarely affects brain function.
1.2. Refsum disease
Refsum disease is an inherited sensorimotor neuropathy characterized by the build-up of phytanic acid. Its prevalence is 1 person per million, and it affects both men and women. The first symptoms usually appear around the age of 15, although they can also appear during childhood or adulthood (between 30 and 40).
Accumulation of phytic 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 recent studies have shown 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 accumulation of sulfates in the central nervous system and kidneys. There are three types: late childhood, youth, and adult. The prevalence of this disorder is estimated at approximately 1 in 625,000 people.
The late infantile form is the most common and usually begins at an age when children are learning to walk, with symptoms such as hypotonia, difficulty walking, optic atrophy, and motor regression preceding cognitive impairment. The peripheral nervous system of these patients is systematically damaged (considerably decreases the speed of nerve conduction).
Acquired demyelinating polyneuropathy they represent a heterogeneous group, with a multitude of types and variants. These diseases can have different causes: toxic (such as heavy metals), 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 polyneuropathy, and one of its most well-known variants is Guillain-Barré disease or syndrome.
Then we will see what are its main characteristics and clinical manifestations.
2.1. Chronic inflammatory demyelinating polyneuropathy (CIDP)
CIDP is, as we have said, one of the most common forms of acquired polyneuropathy. It starts insidiously and usually progresses for at least 2 months. Its course can be recurrent or chronically progressive, and is usually primarily motor, affecting the 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 loss of distal tenderness of the limbs which are progressive and symmetrical.
In addition, this disease usually present with a decrease or sometimes a complete loss of the tendon reflexes. Although there are variants with purely motor impairment, these are the least common (around 10% of cases). The cranial nerves are usually unaffected, and a common symptom is usually bilateral paresis of the facial nerve. Rarely, breathing capacity and urination are also affected.
2.2. Guillain Barre 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 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 appear at any age and in people of all ages. ethnicities and all 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.
The indicated treatment varies depending on the type of demyelinating polyneuropathy and its symptoms and clinical manifestations. In the case of CIDP, treatment usually includes corticosteroids such as prednisone, which can 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 taken from the patient’s body and white blood cells, red blood cells and platelets are processed, making them separating from those of the rest of the plasma. , to then reintroduce them into the blood; and intravenous immunoglobulin therapy, which is commonly used to treat diseases causing immune deficiency, as well as in immunomodulatory therapies.
On another side, physiotherapy can also be helpful in patients with demyelinating neuropathies, as it can improve muscle strength, function and mobility, as well as minimize the muscle, tendon and joint problems that these patients usually suffer from.
- Ardila, A. and Rosselli, M. (2007). Clinical neuropsychology. Editorial El Manual Modern.
- González-Quevedo, A. (1999). Chronic inflammatory demyelinating polyneuropathy: a contribution to the characterization of the disease. Rev Neurol, 28 (8), 772-778.