Symptoms of affection of the peripheral nervous system

The peripheral nervous system is a topographically conditionally allocated extra-cerebral part of the nervous system, which includes the posterior and anterior roots of spinal nerves, spinal nodules, cranial and spinal nerves, nerve plexuses and nerves. The function of the peripheral nervous system consists in conducting nerve impulses from all extero-, proprio- and interoreceptors into the segmental apparatus of the spinal cord and brain and from the central nervous system of regulatory nerve impulses to organs and tissues. Some structures of the peripheral nervous system contain only efferent fibers, others - afferent. However, most peripheral nerves are mixed and contain motor, sensitive and vegetative fibers.

Symptomocomplex lesions of the peripheral nervous system are composed of a number of specific features. Turning off motor fibers (axons) leads to peripheral paralysis of the innervated muscles. When these fibers become irritated, convulsive contractions of these muscles arise (clonic, tonic convulsions, myocciia), the mechanical excitability of the muscles increases (which is determined when the hammer strikes the muscles).

To establish a topical diagnosis, it is necessary to remember the muscles innervated by a certain nerve and the levels of movement of the motor branches of the nerves. At the same time, many muscles are innervated by two nerves, so even with a complete break in the large nerve trunk, the motor function of individual muscles may suffer only partially. In addition, between the nerves there is a rich network of anastomoses and their individual structure in various departments of the peripheral nervous system is extremely variable - the main and loose types according to VN Shevkunenko (1936). When assessing motor disorders, it is also necessary to bear in mind the presence of compensatory mechanisms that compensate and mask the true loss of function. However, these compensatory movements are never fully satisfied in the physiological volume. As a rule, compensation is more achievable in the upper limbs.

Sometimes the source of an incorrect estimate of the volume of active movement may be false movements. After contraction of the muscle-antagonists and their subsequent relaxation, the limb usually returns passively to its original position. This simulates the contraction of the paralyzed muscle. The power of reducing paragonal muscle antagonists can be significant, which is the basis of muscle contractures. The latter are of a different origin. For example, when the nerve trunks are compressed by scars or bone fragments, intense pain is observed, the limb takes a "protective" position, in which the intensity of pain decreases. Prolonged fixation of the limb in this position can lead to the development of antalgic contracture. Contracture can also occur with prolonged immobilization of the limb (with trauma to bones, muscles, tendons), as well as reflexively - with mechanical stimulation of the nerve (with a vast cicatricial inflammatory process). It is a reflex neurogenic contracture (physiopathic contracture). Sometimes there are also psychogenic contractures. It should also be borne in mind the existence of primary-muscle contractures in myopathies, with chronic myositis and polyneuromyositis (by the mechanism of auto-allergic immunological defeat).

Contractures and stiffness of the joints are a big hindrance in the study of motor disorders of the limb, which depend on the defeat of the peripheral nerves. In the case of paralysis due to loss of motor nerve fibers, the muscles become hypotonic, and soon their atrophy (after 2 to 3 weeks from the onset of paralysis) is attached. Decrease or fall deep and superficial reflexes, carried out by the affected nerve.

A valuable sign of nerve damage is a sensitivity disorder in certain areas. Usually, this zone is smaller than the anatomical area of branching of the skin nerves. This is due to the fact that individual areas of the skin receive additional innervation from neighboring nerves ("overlap zones"). Therefore, three zones of sensitivity disturbance are identified. The central, autonomous, zone corresponds to the region of innervation of the nerve under investigation. With complete disturbance of the nerve conduction in this zone, loss of all types of sensitivity is noted. The mixed zone is supplied with both affected and partly neighboring nerves. In this zone, sensitivity is usually only reduced or perverted. The pain sensitivity is best preserved, the tactile and complex types of sensitivity (localization of stimuli, etc.) suffer less, the ability of rough temperature discrimination is violated. An additional zone is predominantly supplied with the neighboring nerve and, least of all, with the affected nerve. Sensitive disorders in this zone are usually not detected.

The limits of sensitivity disorders vary widely and depend on the variations of the "overlapping" of neighboring nerves.

When irritating sensitive fibers, pain and paresthesia occur. Often, with partial damage to sensitive nerves, perception has an inadequate intensity and is accompanied by an extremely unpleasant sensation (hyperpathy). Characteristic for hyperpathy is an increase in the threshold of excitability: a thin differentiation of weak stimuli falls out, there is no feeling of warm or cool, light tactile stimuli are not perceived, there is a long latent period of perception of stimuli. Painful sensations acquire an explosive, harsh character with an intense sense of unpleasantness and a tendency to irradiation. There is an aftereffect: pain continues for a long time after the cessation of irritation.

The phenomenon of nerve irritation can include a painful phenomenon such as causalgia (Pirogov-Mitchell syndrome) - a burning intense pain against a background of hyperpathy and vasomotor-trophic disorders (hyperemia, marbling of the skin, widening of the capillary network of vessels, swelling, hyperhidrosis, etc.). With causalgic syndrome, pain can be combined with anesthesia. This indicates a complete break of the nerve and the irritation of its central segment with a scar, hematoma, inflammatory infiltration, or the development of a neuroma - phantom pains appear. Diagnostic value has in this case a symptom of effleurage (of the type of the phenomenon of Tinel with effleurage along the median nerve).

When lesions of nerve trunks, vegetative-trophic and vasomotor disorders appear in the form of changes in skin color (pallor, cyanosis, hyperemia, marbling), pastness, decrease or increase in skin temperature (this is confirmed by the thermal imaging method), sweating, etc.

[1], [2], [3], [4], [5], [6], [7]