Tunnel syndromes

Compression-ischemic neuropathies include all cases of mononeuropathies united by a common pathogenetic factor - local compression of the nerve. It is most often possible in those places where the primary trunk passes inside natural morphological formations in the form of openings, canals or tunnels (bone, muscle, fibrous), as well as in situations where the nerve changes its course, making a sharp turn, bending over some ligament or dense fibrous edge of the muscle.

Vegetative disorders in compression-ischemic lesions of the extremities are associated with a damaging effect not only due to mechanical traumatization of the nerve by surrounding tissues. Disorders of nerve functions are also largely due to nerve ischemia and venous congestion, developing tissue edema. In this case, the ischemia factor can follow the primary compression of tissues surrounding the nerve, as occurs in carpal tunnel syndrome. Another sequence is also possible: ischemia acts as the initial link in the pathological process, then intracanal edema and secondary compression of the nerve develop. There is a third option, in which the nerve trunk and the accompanying arterial vessel are simultaneously compressed.

There are some types of tunnel compression-ischemic neuropathies for which autonomic disorders are most characteristic.

Neuropathies of the median nerve

Neuropathies of the median nerve are possible with damage at three levels: in the distal part of the forearm, in its proximal part and in the lower third of the shoulder. Compression-ischemic damage to the median nerve in the distal part of the forearm occurs in the carpal tunnel; in the proximal part of the forearm - its upper third (round pronator syndrome, Seyfarth syndrome) damage occurs when the nerve is pinched by two bundles of the round pronator, usually after significant muscle strain, for example, in pianists (pronation with simultaneous work of the finger flexors). Clinical manifestations of the round pronator syndrome consist of sensory and motor disorders.

Compression-ischemic neuropathy of the median nerve in the lower third of the shoulder occurs when the nerve is damaged in the canal formed by the medial intermuscular septum, the distal and anterior surface of the medial condyle and the so-called Straser ligament. Vegetative disorders in neuropathy of the median nerve are characterized by diversity and severity. The pain is acute, burning, sometimes occurs in attacks and is accompanied by pronounced vasomotor disorders in the form of cyanosis, swelling of the fingers and pronounced subjective sensations of numbness and paresthesia.

Neuropathies of the ulnar nerve

Neuropathies of the ulnar nerve occur due to compression in the distal part of the hand - ulnar tunnel syndrome of the wrist (Guyon's bed syndrome) and in the proximal part at the elbow level (cubital tunnel syndrome).

Radial Nerve Neuropathies

Radial nerve neuropathies most often develop as a result of nerve entrapment in the spiral canal at the level of the middle third of the shoulder.

The following compression-ischemic neuropathies are distinguished in the lower limbs: external cutaneous nerve of the thigh (meralgia paresthetica of Roth); common peroneal nerve (Guillain de Seza syndrome, Blondin-Walter syndrome); plantar nerves; interdigital nerves (Morton's metatarsalgia); distal part of the tibial nerve (tarsal canal syndrome, Richet canal syndrome).

Etiology and pathogenesis of tunnel syndromes. Tunnel neuropathies can be congenital, genetically determined. However, much more often the cause of nerve compression are acquired factors, acting long-term or short-term, general and local diseases, injuries and their consequences, occupational diseases. Endocrine changes are of significant importance in the etiology of compression neuropathies, as evidenced by their frequency in elderly women in the climacteric period, in pregnant women, in women with ovarian failure. Of decisive importance in this case is the weakening of the inhibitory effect of sex hormones on the secretion of the somatotropic hormone of the pituitary gland, which in these situations is secreted in excess, stimulating swelling and hyperplasia of the connective tissue, including inside the tunnel. Similar changes can result from the narrowing of the nerve receptacles observed in collagenoses due to the proliferation of connective tissue. This factor becomes especially important in old age, when muscle fibrosis naturally occurs.

Among the local causes influencing the formation of compression-ischemic neuropathies are the consequences of injuries to bones, muscles and tendons, overstrain of the muscular-ligamentous apparatus, iatrogenic effects due to improper application of a tourniquet, a blind plaster cast, due to rough manipulations during repositioning of bone fragments during osteosynthesis. A frequent cause may be repeated mechanical irritation of the nerve trunk in the area most fixed by surrounding tissues.

The pathogenesis of compression-ischemic neuropathies is quite complex. Compression of the nerve in the tunnels is caused by pathological changes in the ligaments, tendons and their sheaths surrounding the nerve, muscles, and bones that form the corresponding canal: an increase in the volume of perineural tissues (mechanical phenomenon), an increase in tissue intracanal pressure (physical phenomenon), disturbances in the blood supply to the nerve (ischemia and disturbance of venous outflow), hyperfixation of the nerve in a certain section of the tunnel with limitation of its mobility along its length (compression-traction mechanism).

In all cases of peripheral neuropathies, the severity of vegetative disorders in the extremities depends on the number of vegetative fibers in the peripheral nerve, the compression of which forms the corresponding neuropathic syndrome. The most vivid clinical picture is revealed in lesions of the median nerve in the arm and the peroneal nerve in the leg, which determines the richness of the vegetative accompaniment of the corresponding tunnel neuropathies.