Motor neuron diseases

Motoneuron diseases are characterized by steadily progressing degeneration of cortico-spinal tracts, anterior horn neurons, bulbar motor nuclei or a combination of these lesions. Among the symptoms: muscle weakness and atrophy, fasciculation, emotional lability and weakness of the respiratory muscles. Diagnosis includes examination of the rate of excitation, EMG and exclusion of other disorders in neuroimaging and in laboratory tests. Treatment of motor neuron disease is symptomatic.

Causes of the motor neuron diseases

There are several forms of motor neuron disease, and their etiology is often unknown. The nomenclature and symptoms depend on the localization of the primary lesion. Among myopathies, simulating the clinical picture of motor neuron disease, muscular membrane damage, contractile apparatus and organelles of myocytes.

[1]

Symptoms of the motor neuron diseases

It is accepted to distinguish between the lesion of the upper (central) and lower (peripheral) motoneuron; sometimes (for example, with amyotrophic lateral sclerosis) both neurons are affected.

When the upper motoneuron is affected (for example, primary lateral sclerosis), neurons suffer from the motor cortex to the brainstem (corticobulbar tracts) or the spinal cord (corticospinal tracts). Among the symptoms of stiffness, difficult and awkward movements, first the muscles of the mouth, throat, sweat and limbs.

With lesions of the lower motoneuron, the neurons of the anterior horn of the spinal cord or their efferent axons, which go to the skeletal muscles, suffer. In bulbar paralysis, only the bulbar nuclei of the cranial motor nerves are affected in the brainstem. Common complaints are weakness of facial muscles, dysphagia and dysarthria. When the neurons of the anterior horns are affected, as in the case of spinal amyotrophy, complaints of weakness and atrophy, fasciculations (visible small muscle twitches), and krampi in hands, feet, or tongue are common. To diseases of the lower motoneuron also include poliomyelitis and enterovirus infection, when the neurons of the anterior horns are affected, and post-poliomyelitis syndrome.

Physical examination helps differentiate the lesions of the upper and lower motoneuron, as well as weakness in the lesions of the lower motoneuron from weakness in myopathies.

Forms

Amyotrophic lateral sclerosis (ALS)

ALS (Lou Gehrig's disease, Charcot's syndrome) is the most common form of motor neuron failure. The disease begins with asymmetric cramps, weakness and amyotrophy of the brushes (more often) or stop. Then there are fasciculations, spasticity, increased deep tendon reflexes, extensor plantar reflexes, stiffness of movements, weight loss, fatigue and difficulty in controlling the expression of the face and movements of the tongue. Other symptoms include dysphonia, dysphagia, dysarthria and choking with liquid food. Then there appear inappropriate, involuntary and uncontrolled (pseudobulbar syndrome) fits of laughter or crying. Sensitivity, consciousness, cognitive sphere, arbitrary eye movements, sexual function, and also the function of sphincters are usually not violated. Death occurs due to paralysis of the respiratory muscles, half of the patients die in the first 3 years from the debut of the disease, 20% live 5 years, and 10% - 10 years. Survival for 30 years is a rarity.

[2], [3], [4],

Progressive Bulbar Palsy

Violations of the function of the muscles innervated by the cranial nerves and corticobulbar pathways cause progressive difficulties in chewing, swallowing, talking, there is a nasal voice, a decrease in the emetic reflex, fasciculation and weakness of the facial muscles, and also the tongue. When the cortico-bulbar path is affected, pseudobulbar paralysis develops with emotional lability. With dysphagia, the prognosis is poor, respiratory complications resulting from aspiration lead to death in 1-3 years.

Progressive muscular atrophy

In many cases, especially if the disease debuts in childhood, it is inherited by an autosomal recessive type. In other cases, it appears sporadically. In general, the disease can develop at any age. It is possible to defeat only the neurons of the anterior horns or it is more pronounced than the concomitant defeat of the cortico-spinal pathways. The disease progresses more slowly than other motoneuron lesions. The earliest manifestation can be fasciculations. Muscle weight loss and weakness begin with brushes, then spread to the arms, shoulders and legs. Survival is usually more than 25 years.

Primary lateral sclerosis and progressive pseudobulbar paralysis

With progressive pseudobulbar paralysis, the tension and weakness in the distal sections gradually increase, affecting the limb, as well as the muscles innervated by caudal cranial nerves. Much later, fasciculations and muscle atrophy may appear. After a few years, these violations lead to complete disability.

Diagnostics of the motor neuron diseases

The disease should be suspected with progressive generalized motor weakness, not accompanied by significant impairment of sensitivity. Among other neurological diseases leading to isolated muscle weakness, neuromuscular transmission disorders and various myopathies. Acquired causes of only motor weakness: noninflammatory myopathies, polymyositis, dermatomyositis, thyroid and adrenal disorders, electrolyte disorders (hypokalemia, hypercalcemia, hypophosphatemia) and various infections (eg syphilis, Lyme disease, hepatitis C).

In the defeat of cranial nerves, the secondary cause is less likely. Symptoms of lower and upper motoneuron failure, as well as weakness of facial muscles, support amyotrophic lateral sclerosis.

Electrodiagnostics studies are performed to exclude neuromuscular transmission disorders and demyelination of nerves. When MN is affected, the rate of excitation is usually not up to the late stage of the disease. The most informative needle EMG, showing fibrillation, positive waves, fasciculations, and sometimes giant potentials of action of motor units, even in outwardly unaffected limbs.

An MRI is required. In the absence of clinical and EMG data, indicating the defeat of cranial nerves, MRT of the cervical department is prescribed.

To detect potentially curable diseases, a general blood test is performed, the level of electrolytes, creatine phosphokinase, thyroid hormones, protein in serum and urine, electrophoresis with immunofixation for monoclonal antibodies, detect antibodies to myelin-associated glycoprotein (MAG), and if there is a suspicion of intoxication with heavy metals, then examine their content in daily urine. A lumbar puncture should be performed: a high content of leukocytes or protein suggests a different diagnosis.

At the slightest suspicion, a VDRL reaction to syphilis is carried out, ESR, rheumatoid factor, antibodies to Borrelia, HIV, hepatitis C virus, antinuclear antibodies (ANA), antibodies to neuronal antigens appearing within the paraneoplastic syndrome (anti Hu). Genetic testing (for example, superoxide dismutase gene mutation) and enzyme determination (eg, hexosaminidase A) is only indicated if the patient is interested in genetic counseling, and the results of these studies can not affect treatment in any way.

[5], [6], [7], [8], [9]

Treatment of the motor neuron diseases

There is no specific treatment for motor neuron disease. Antiglutamate preparation riluzole 50 mg orally 2 times / day prolongs life with bulbar form of amyotrophic lateral sclerosis. Confronting progressive neurological dysfunction follows the forces of specialists of various profiles. Physiotherapy helps maintain muscle function. It is important to recommend orthopedic fixation bandages and walking aids. A speech therapist can pick up adequate communication devices. With pharyngeal weakness, eating is a real threat and percutaneous endoscopic gastrostomy may be required.

With the development of respiratory weakness, the pulmonologist will recommend non-invasive respiratory support (eg, a two-level positive pressure), tracheostomy or complete ventilation.

Baclofen reduces spasticity, quinine or pheniton can weaken the crump. Anticholinergic drugs (eg, glycopyrrolate, amtriptyline, benzthropine, trihexyphenidyl, hyoscine applications, atropine) reduce salivation. Amitriptyline and fluvoxamine are used for pseudobulbar lesions. In the late stages of these diseases, pain may require the appointment of opioids and benzodiazepines. Surgical intervention to improve swallowing with progressive tabloid paralysis is ineffective.

To determine the level of permissible intervention, the attending physician already in the early stages of the disease of motor neuron disease should frankly talk with the patient, his family members and caregivers. Subsequently, these decisions should be periodically reviewed and confirmed.