Hereditary neuropathies

Hereditary neuropathies are congenital degenerative neurological disorders.

A distinction is made between sensorimotor and sensory hereditary neuropathies.

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Forms

Sensorimotor neuropathies

There are three types (I, II and III), which begin in childhood. Less common types begin at birth and lead to more severe disability.

Types I and II (peroneal amyotrophy, Charcot-Marie-Tooth disease, or CMT disease) are the most common, with an autosomal dominant type of inheritance. Weakness and atrophy are typical, mainly of the peroneal and distal leg muscles. The patient or his family history may also have other degenerative diseases (eg, Friedreich's ataxia). CMT type I disease debuts in childhood with weakness in the feet and slowly progressing distal amyotrophy (stork legs). Characteristic amyotrophy of the hands develops later. Vibration, temperature and pain sensitivity are impaired in a stocking-glove pattern.

Deep tendon reflexes are lost. Sometimes the only signs of the disease are foot deformities (high arches to a "hollow" foot) with hammertoes. The speed of nerve impulse conduction is slow, and distal latency is prolonged. Segmental demyelination and remyelination occur. Thickened peripheral nerves can be palpated. The disease progresses slowly and does not reduce life expectancy. Type II CMT progresses more slowly, weakness develops later. The speed of excitation conduction is relatively normal, but the amplitude of sensory nerve action potentials is reduced, polyphasic muscle action potentials are determined. Biopsy shows Wallerian degeneration of axons.

Type III (hypertrophic neuropathy, Dejerine-Sottas disease) is a rare autosomal recessive disorder that begins in childhood with progressive weakness, sensory loss, and absence of deep tendon reflexes. It initially resembles CMT, but muscle weakness progresses more rapidly. Demyelination-remyelination leads to thickening of the peripheral nerves, which is visible in biopsy material.

Hereditary motor neuropathy with liability to pressure palsies is an inherited disorder in which nerves become increasingly sensitive to pressure and stretch.

In hereditary motor neuropathy with a tendency to pressure palsies, nerves lose their myelin sheath and the ability to conduct impulses normally. The incidence is 2-5 cases per 100,000 inhabitants.

The cause is the loss of one copy of the peripheral myelin protein 22 (PMP22) gene, located on the short arm of chromosome 17. Two copies of the gene are needed for normal functioning. At the same time, duplication (the appearance of an additional copy of the gene) is manifested by the development of CMT type I disease.

Pressure paralysis can be mild or severe and can last from minutes to months. Numbness and weakness are felt in the affected areas.

The disorder should be suspected in the presence of recurrent demyelinating polyneuropathy, compressive mononeuropathy, multiple neuropathies of unknown origin, or a family history of carpal tunnel syndrome. EMG, nerve biopsy, and genetic testing are helpful in diagnosis, but biopsy is rarely required. Treatment is symptomatic, with avoidance of any activity that may cause complaints. Wrist splinting may relieve pressure, prevent recurrent injury, and allow myelin to regenerate over time. Surgery is rarely indicated.

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Sensory neuropathies

In rare hereditary sensory neuropathies, the loss of pain and temperature sensation in the distal areas is more pronounced than the loss of vibration and localization sensation. The main complication is mutilation of the foot due to the lack of sensation, which is fraught with the risk of infection and osteomyelitis.

Diagnostics hereditary neuropathies

The diagnosis is aided by the characteristic distribution of muscle weakness, foot deformities, family history, and electrophysiological studies. There is a method of genetic analysis.

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Treatment hereditary neuropathies

There is no specific treatment. Bracing can help correct the weakness of the foot, and orthopedic surgery can stabilize the foot. Consultations with a medical psychologist are useful in preparing young patients for the progression of the disease.