Motor neuropathy

Motor neuropathy or motor neuropathy, which is distinguished among neurological disorders, is defined as a disorder of reflex-motor functions, which are provided by various structures of the nervous system.

Pathologies of movement may involve damage to the subcortical motor nuclei involved in the conduction of nerve impulses, the cerebellum, the pyramidal system, the reticular formation of the brainstem, the peripheral nerves innervating the skeletal muscles, motor neurons and their processes (axons).

Epidemiology

According to clinical statistics, peripheral motor neuropathy in diabetes mellitus develops over time in six out of ten patients with this disease.

According to the Journal of Neurology, the human immunodeficiency virus causes neuropathic conditions in a third of patients. Multiple motor neuropathy is detected in three people per 100 thousand of the population and affects males almost three times more often.

The most common inherited disorder of the peripheral nerves, Charcot-Marie-Tooth disease, affects approximately one in 2.5 to 5 thousand people.

In North America, spinal muscular atrophy affects one in 6,000 to 8,000 babies each year. Some estimates suggest that one in 40 to 50 people is an asymptomatic carrier of the disease, meaning they have a defective gene that can be passed on to their children as an autosomal dominant trait.

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Causes motor neuropathy

In many cases, the causes of motor neuropathy are motor neuron diseases. These nerve cells are divided into upper (in the brain) and lower (spinal); the former transmit nerve impulses from the nuclei of the sensorimotor cortex of the brain to the spinal cord, and the latter relay them to the synapses of muscle fibers.

In case of degenerative changes of upper motor neurons, primary lateral sclerosis and hereditary spastic paraplegia are observed. In case of degenerative lesions of spinal motor neurons, focal spinal motor neuron syndrome or amyotrophic lateral sclerosis syndrome, multiple motor neuropathy and distal spinal amyotrophy develop. Etiologically homogeneous syndromes are also distinguished: Werdnig-Hoffman (begins in children up to six months), Dubowitz (begins at 6-12 months), Kugelberg-Welander (may appear between 2 and 17 years), Friedreich's ataxia (appears by the end of the first decade of life or later). In adults, the most common type of spinal amyotrophy is considered to be slowly progressive Kennedy's disease (also called spinobulbar muscular atrophy).

Motor neuropathy is associated with degeneration of the cerebellum, which controls muscle tone and coordination of movements. It manifests itself as a hereditary movement disorder or ataxia, as a symptom of multiple sclerosis, as a neurological consequence of acute cerebrovascular accident, for more details see – Ischemic neuropathy

Movement disorders may occur in oncological diseases, in particular, in the form of paraneoplastic neurological syndrome Eaton-Lambert. See - Causes of cerebellar ataxia.

Patients who have suffered traumatic brain injuries or poisoning with various toxic substances; those who have contracted infectious diseases, among the pathogens of which are polyomavirus, Varicella and Herpes zoster viruses, Human immunodeficiency virus (HIV), Cytomegalovirus, as well as the bacteria Borrelia burgdorferi, Mycoplasma hominis, Campylobacter jejuni, Treponema pallidum (causing neurosyphilis) often encounter impaired motor functions as a neurological complication.

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Risk factors

Among the risk factors for the development of motor neuropathy, experts name disorders of the immune system with the activation of autoimmune reactions, loss of myelin sheaths of nerve fibers and axons of motor neurons.

At risk are the elderly, alcohol addicts, children in families with hereditary neurological disorders, cancer patients with lymphomas and lung cancer, most patients after cancer treatment with ionizing radiation and cytostatics. Details in the article - Polyneuropathy after chemotherapy

The risk of neurological motor disorders in diabetics is extremely high. Motor neuropathy in diabetes mellitus is discussed in detail in the publication - Diabetic neuropathy

Other diseases with motor neurological complications include celiac disease, amyloidosis, megaloblastic anemia (vitamin B12 deficiency), and lupus (SLE).

The risk should be taken into account when using some medications that can cause sensory-motor dysfunction. For example, this is the drug Disulfiram (against alcoholism), Phenytoin (anticonvulsant), anticancer drugs (Cisplatin, Vincristine, etc.), the drug for hypertension Amiodarone, etc.

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Pathogenesis

In cases of hereditary spinal amyotrophy, the pathogenesis lies in the degeneration of spinal motor neurons and a portion of the brainstem, which occurs due to mutations in the SMN1 gene at locus 5ql3, encoding the SMN protein complex of motor neuron nuclei, the decrease in the levels of which leads to the death of these cells. Amyotrophy may develop due to defects in the motor nuclei of the cranial nerves and effector nerve endings (neuromuscular synapses). Muscle weakness - with a decrease in their tone, weakening of tendon reflexes and possible atrophy - may be a consequence of the limited release of the acetylcholine mediator from the axons of motor neurons into the synaptic cleft.

Pathophysiological mechanisms of immunologically conditioned neuropathies include aberrant cellular and humoral immune responses. Thus, the development of multifocal and axonal motor neuropathy is associated with the formation of IgM antibodies to the myelin sheaths of axons of motor neurons and peripheral nerves. Myelin contains gangliosides GM1, GD1a, GD1b - complex compounds of sphingolipids and oligosaccharides. It is assumed that antibodies are produced specifically for ganglioside GM1 and can interact with it, activating the immune system of complement and blocking ion channels. Since the level of GM1 in the sheaths of axons of motor neurons is higher than in the sheaths of sensory neurons, then, probably, the fibers of motor nerves are more susceptible to attack by autoantibodies.

Also read – Chronic inflammatory demyelinating neuropathy.

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Symptoms motor neuropathy

Different types of motor neuropathy exhibit certain similar manifestations characteristic of motor function disorders.

The localization and etiology of the disease determine the early symptoms. For example, the first signs of amyotrophic lateral sclerosis are manifested by progressive weakness and stiffness of the arms and legs, which leads to dysbasia - slow walking with impaired coordination of movements and balance (a person often stumbles on level ground).

In hereditary spinal muscular atrophy in adults, the symptoms of motor neuropathy include periodic twitching of superficial muscle fibers (fasciculations) against the background of their decreased tone and weakening of tendon reflexes. At a later stage - as the disease progresses - muscle weakness that limits movement begins to be felt not only in the arms and legs, but also in other muscle groups (including intercostal respiratory, pharyngeal, orofacial). Because of this, breathing problems occur, progressing to respiratory failure, and dysphagia (difficulty swallowing). Speech also slows down and becomes slurred. The list of typical symptoms of Kennedy disease - with genetically determined degeneration of motor neurons in the spinal cord and brainstem - includes weakness and atrophy of the muscles of the limbs, face, pharynx, larynx and oral cavity. Speech (dysarthria) and swallowing (dysphagia) disorders are noted.

Multiple or multifocal motor neuropathy is manifested by unilateral movement disorder of the limbs, without sensory symptoms. In eight cases out of ten, the disease begins at 40-50 years of age. The ulnar, median and radial nerves are most often affected, with weakness in the hands and wrists, making fine motor skills difficult. Lewis-Sumner syndrome is distinguished, which is essentially a multiple motor-sensory neuropathy of an acquired (inflammatory) nature with paresthesia of the upper limbs and decreased skin sensitivity of the back of the hands. More information in the article - Neuropathy of the upper limbs

Motor neuropathy of the lower extremities, as a widespread type of neurological disorder, is discussed in detail in the publication - Neuropathy of the Legs

Some immunologically conditioned neuropathies may have acute and chronic forms. Acute axonal motor neuropathy caused by dysfunction of neuronal processes is still diagnosed as a subtype or variant of Landry-Guillain-Barré polyneuropathy or Guillain-Barré syndrome (acute polyradiculoneuritis) – with symptoms in the form of progressive muscle weakness of the distal parts of the upper limbs, fasciculations, partial tendon areflexia, limited eye movement, flaccid tetraplegia (paralysis of all limbs) in the absence of a nerve impulse conduction block. Signs of demyelination and sensory impairments are absent in this pathology.

Chronic idiopathic axonal motor polyneuropathy is a common neurological disorder in older adults (over 65 years of age) that presents with symmetrical distal symptoms in the lower extremities in the form of ankle clonus, muscle weakness and stiffness when walking, painful cramps in the calf muscles (cramps) at rest, and cramps in the anterior tibialis muscles after walking.

Due to pathological processes leading to the disruption of individual sections of the myelin sheaths of the processes of motor neurons (as well as the roots and fibers of the spinal nerves innervating the muscles), motor axonal-demyelinating neuropathy may develop with symptoms such as: involuntary twitching of the muscles of the limbs, their paresthesia (tingling and numbness), impaired tactile and temperature sensitivity (especially of the hands and feet), paresis (partial paralysis), paraplegia (simultaneous paralysis of both arms or both legs), orthostatic dizziness, dysbasia and dysarthria. Vegetative signs may manifest themselves as increased sweating and acceleration/deceleration of the heart rate.

Forms

When efferent (motor) and afferent (sensory) neurons and nerve fibers lose the ability to transmit signals, which most often occurs in children and adolescents with hereditary neuropathies, peripheral motor-sensory neuropathy is diagnosed, which is divided into several types of genetically determined diseases.

Motor-sensory neuropathy type 1 – hypertrophic-demyelinating, which accounts for half of all inherited peripheral neuropathies in children – is associated with segmental demyelination caused by impaired synthesis of myelin proteins due to gene mutations on chromosomes 17p11.2, 1q21-q23 and 10q21.

This type of pathology, which is characterized by hypertrophy of the peripheral nerves, is a slowly progressive atrophy of the peroneal (fibular) muscles of the lower extremities - Charcot-Marie-Tooth disease type 1. It is characterized by atrophy of the leg muscles below the knee in the ankle area (with the formation of a pathologically high arch of the foot and a characteristic change in the shape of the toes); tremor often occurs with tension; anhidrosis (absence of sweat) and progressive hypesthesia are noted, and in some cases - loss of pain sensation (in the distal parts of the lower extremities); tendon reflexes of the Achilles ligament disappear; signs of mental and psychic disorders appear; rarely the disease is accompanied by nervous deafness. In the later stages, the muscles of the arms below the elbow also atrophy with deformation of the hands.

Hereditary motor-sensory neuropathy type 2 (Charcot-Marie-Tooth disease type 2) is an axonal amyotrophy, i.e. associated with dysfunction and degeneration of the processes of motor and sensory neurons without loss of the myelin sheath. It affects the same muscle group and manifests itself between the ages of 5 and 25. Mutations have been identified on chromosomes 1p35-p36, 3q13-q22 and 7p14.

Against the background of almost normal nerve impulse conduction velocity (compared to the first type of the disease), clinical manifestations of distal muscle weakness and atrophy are less pronounced; muscle atrophy below the knee is symmetrical in 75% of patients; typical first signs are weakness of the feet and ankles, decreased tendon reflexes with weakness of dorsiflexion of the foot at the ankle. Mild sensory symptoms are present; pain, sleep apnea, restless legs syndrome, and depression may be observed. Muscle atrophy of the arms is rare.

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Complications and consequences

Previously, neurologists believed that motor neuron disease does not affect the functioning of the brain, but research results have shown that this opinion is wrong. It turned out that the negative consequences and complications of amyotrophic lateral sclerosis and degenerative changes in the lower motor neurons in almost half of patients manifest themselves in some kind of CNS disorder, and in 15% of cases, frontotemporal dementia develops. Changes in personality and emotional state with attacks of uncontrollable crying or laughter may appear.

Impaired contractions of the main respiratory muscle (the diaphragm) cause breathing problems in amyotrophic lateral sclerosis; patients also experience increased anxiety and sleep disturbances.

Complications of the axonal-demyelinating form of neuropathy are manifested by impaired intestinal motility, urination and erectile dysfunction.

Damage to sensory nerves can lead to loss of pain sensitivity, and untreated injuries and wounds due to infectious inflammation can lead to gangrene and sepsis.

In Charcot-Marie-Tooth disease, the joints cannot respond normally to pressure, causing microcracks in bone structures, and the destruction of bone tissue leads to irreversible deformation of the limbs.

Spinal muscular atrophy is considered the second most significant cause of childhood mortality in the world. If the degree of pathology is insignificant, the patient survives - most often with the subsequent loss of the ability to move independently.

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Diagnostics motor neuropathy

In the early stages, neurological movement disorders are difficult to diagnose because their symptoms are similar to those of other conditions, such as multiple sclerosis, neuritis, or Parkinson's disease.

Diagnostics begins with examination and testing of tendon reflexes. Laboratory tests are required: biochemical and general blood tests, analysis of the level of creatinine phosphokinase in plasma, C-reactive protein, antibody levels (in particular, antibodies to ganglioside GM1), complement C3, etc. If necessary, a cerebrospinal fluid analysis is taken.

The main instrumental diagnostics used in neurology include: stimulation electromyography (EMG); electroneuromyography (ENMG); myelography; ultrasound and MRI scanning of the brain (to exclude stroke, cerebral neoplasia, circulatory problems or structural abnormalities); positron emission tomography (PET).

Some motor neuropathies are classified as variants of amyotrophic lateral sclerosis, but differential diagnosis is necessary. Among neuropathies of immune genesis with destruction of myelin sheaths, multifocal motor neuropathy and chronic immune demyelinating polyneuropathy should be differentiated.

Lower motor neuron loss involving sensory nerves must be distinguished from paraneoplastic encephalomyelitis and sensory ganglionic syndromes.

In addition, it is necessary to exclude myopathic syndromes and muscular dystrophies, for which a muscle study is carried out, as well as Morvan's disease (syringomyelia) - using MRI of the spine, visualizing the spinal cord.

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Treatment motor neuropathy

Neurologists admit that today only symptomatic treatment of motor neuropathy is possible, alleviating the condition of patients and somewhat slowing down the progression of pathological processes. And there are no drugs yet for the treatment of hereditary motor and sensory neuropathies.

One of the generally accepted methods is periodic plasmapheresis, which removes autoantibodies from the patients' blood.

In multiple motor neuropathy, human immunoglobulin (IVIg) is administered by infusion; glucocorticoids (Prednisolone or Methylprednisolone), which have an immunomodulatory effect, can be used systemically. Vitamins A, D, and group B are prescribed for all types of movement disorders.

Some other medications are also used. First of all, L-carnitine is prescribed for oral administration to normalize tissue metabolic processes and restore damaged cells: for adults in the form of capsules (0.25-0.5 g twice a day), for children in the form of syrup (the dose is determined by the doctor depending on age).

To increase the conductivity of nerve impulses, the CNS stimulating inhibitor of the cholinesterase enzyme Ipidacrine (other trade names: Neurodimin, Amipirin, Axamon) is used orally or parenterally: adults - 10-20 mg three times a day (or 1 ml intramuscularly); children from one year to 14 years old are allowed only oral use - a single dose is 10 mg (half a tablet) - up to three times during the day. The course of treatment lasts one to one and a half months; Ipidacrine can be re-prescribed two months after the end of the first course.

This drug is contraindicated in cases of heart rate disorders, inflammatory gastroenterological and pulmonary diseases, and pregnancy. And its most likely side effects include nausea, diarrhea, dizziness, salivation, and bronchial spasms.

Recently, foreign neurologists have been prescribing a new drug (approved by the FDA) Riluzole (Rilutek) to patients with amyotrophic lateral sclerosis. Its effectiveness and even the mechanism of action are still poorly understood, and the list of complications of its use includes a number of serious side effects.

Useful information from the material - Treatment of diabetic neuropathy and publications - Treatment of neuropathy of the upper extremities

Treatment of hereditary motor-sensory disorders requires the involvement of not only a neurologist but also a physiotherapist. Physiotherapy treatment can play an important role in slowing down and preventing the progression of the disease and managing symptoms, and the treatment plan should focus on strengthening the affected muscle group. This may include therapeutic massage, exercise therapy, ultrasound, electrical stimulation, water therapy, pelotherapy, etc.

Many patients require orthopedic assistance: orthopedic shoes or ankle and foot orthoses are needed to support the arch when walking; crutches, canes or walkers are often needed; some require a wheelchair.

In cases of severe limb deformities, surgical treatment is undertaken.

For those who prefer folk remedies, it is recommended to use bee venom – treatment with bee stings

However, it should be borne in mind that the effectiveness of honey bee venom (with its active substance melittin) has only been proven for peripheral neuropathies caused by chemotherapy.

But massage with essential oils of chamomile and lavender (a few drops per dessert spoon of the main oil) helps with paresthesia in movement disorders.

In the same way, herbal treatment helps with neuropathies induced by the use of anticancer drugs. The following medicinal plants are used:

• Common sage (Salvia officinalis), which contains apigenin, which has significant antioxidant activity and protects nerve cells of the peripheral nervous system;
• calamus (Acorus calamus), the extract of which relieves pain, calms and relieves cramps;
• Ginkgo biloba (Ginkgo biloba), which contains terpene trilactones, which have a positive effect on damaged neurons.

In case of progressive spinal amyotrophy, homeopathy can also be used, recommending such patients the following preparations: Argentum nitricum, Plumbum, Phosphorus, Kali phosphoricum, Cuprum, Arnica montana. But they are also unable to help with genetically “programmed” pathologies that cause motor function disorders.

Prevention

There is no way to prevent hereditary spinal muscular atrophy or immune-mediated demyelination of motor neurons and their axons.

The issue of their prevention is genetic counseling of families in which there are carriers of abnormal genes. For this, a blood test is carried out, and antenatal screening can be carried out, that is, an examination of a pregnant woman using chorionic villus sampling (CVS).

More information in the article – Genetic analysis during pregnancy

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Forecast

The prognosis for the development of the disease depends on the cause of motor neuropathy, the degree of damage to the structures that ensure the conduction of nerve signals and the reflex-motor functions of the central nervous system.

Very often these diseases progress rapidly, and the functional defect is so significant that patients become disabled.

Hereditary motor-sensory neuropathies do not reduce life expectancy, but associated pathologies cause various complications of the neurological disorder.

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