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Peripheral neuropathies are classified on the basis of the structure that is primarily affected. The predominant pathologic feature may be axonal degeneration (axonal or neuronal neuropathies) or paranodal or segmental demyelination. The distinction may be possible on the basis of neurophysiologic findings.
Peripheral neuropathies may also occur as a result of disorders affecting the connective tissues of the nerves or the blood vessels supplying the nerves.
Nerves may be injured or compressed by neighboring anatomic structures at any point along their course. Common mononeuropathies of this sort are considered below. They lead to a sensory, motor, or mixed deficit that is restricted to the territory of the affected nerve. A similar clinical disturbance is produced by peripheral nerve tumors, but these are rare except in patients with Recklinghausen's disease. Multiple mononeuropathies suggest a patchy multifocal disease process such as vasculopathy (eg, diabetes, arteritis), an infiltrative process (eg, leprosy, sarcoidosis), radiation damage, or an immunologic disorder (eg, brachial plexopathy). Diffuse polyneuropathies lead to a symmetric sensory, motor, or mixed deficit, often most marked distally. They include the hereditary, metabolic, and toxic disorders; idiopathic inflammatory polyneuropathy (Guillain-Barre Guillain-Barré syndrome); and the peripheral neuropathies.
Polyneuropathies and Mononeuritis Multiplex
The cause of polyneuropathy or mononeuritis multiplex is suggested by the history, mode of onset, and predominant clinical manifestations. Laboratory workup includes a complete blood count and sedimentation rate, serum protein electrophoresis, determination of plasma urea and electrolytes, liver and thyroid function tests.
Treatment is of the underlying cause, when feasible, and is discussed below under the individual disorders. Physical therapy helps prevent contractures, and splints can maintain a weak extremity in a position of useful function. Anesthetic extremities must be protected from injury.
Neuropathic pain is sometimes troublesome and may respond to simple analgesics such as aspirin. Narcotics or narcotic substitutes may be necessary for severe hyperpathia or pain induced by minimal stimuli, but their use should be avoided as far as possible. The use of phenytoin, carbamazepine, or tricyclic antidepressants.
Symptoms of autonomic dysfunction are occasionally troublesome. Postural hypotension is often helped by wearing waist-high elastic stockings and sleeping in a semierect position at night. Fludrocortisone reduces postural hypotension, but doses as Indomethacin (25 or 50 mg three times daily).
Inherited Neuropathies
Charcot-Marie-Tooth Disease: Several distinct varieties of Charcot-Marie-Tooth disease can be recognized.
Dejerine-Sottas Disease (HMSN Type III): Most cases are sporadic or autosomal recessive. The recessive form has its onset in infancy or childhood and leads to a progressive motor and sensory polyneuropathy with weakness, ataxia, sensory loss, and depressed or absent tendon reflexes.
Friedreich's Ataxia: Patients generally present in childhood or early adult life with this autosomal recessive disorder, which has been related to a genetic defect on the long arm of chromosome 9.
Refsum's Disease (HMSN Type IV): This autosomal recessive disorder is due to a disturbance in phytanic acid metabolism. Clinically, pigmentary retinal degeneration.
Porphyria: Peripheral nerve involvement may occur during acute attacks in both variegate porphyria and acute intermittent porphyria. Motor symptoms usually occur first, and weakness is often most marked proximally and in the upper limbs.
Neuropathies Associated With Systemic & Metabolic Disorders
A. Diabetes Mellitus: In this disorder, involvement of the peripheral nervous system may lead to symmetric sensory or mixed polyneuropathy, asymmetric motor neuropathy.
Sensory polyneuropathy, the most common manifestation, may lead to no more than depressed tendon reflexes and impaired appreciation of vibration in the legs. When symptomatic, there may be pain, paresthesias, or numbness in the legs, but in severe cases distal sensory loss occurs in all limbs. Diabetic amyotrophy is characterized by asymmetric weakness and wasting involving predominantly the proximal muscles of the legs, accompanied by local pain. Thoracoabdominal radiculopathy leads to pain.
Chronic Inflammatory Polyneuropathy
Chronic inflammatory demyelinating polyneuropathy, an acquired immunologically mediated disorder, is clinically similar to Guillain-Barre Guillain-Barré syndrome except that it has a relapsing or steadily progressive course over months or years. In the relapsing form, partial recovery may occur.
2. Mononeuropathies
An individual nerve may be injured along its course or may be compressed, angulated, or stretched by neighboring anatomic structures, especially at a point where it passes through a narrow space (entrapment neuropathy). The relative contributions of mechanical factors and ischemia to the local damage are not clear. With involvement of a sensory or mixed nerve, pain is commonly felt distal to the lesion. Symptoms never develop with some entrapment neuropathies, resolve rapidly and spontaneously in others, and become progressively more disabling and distressing.
In chronic compressive or entrapment neuropathies, avoidance of aggravating factors and correction of any underlying systemic conditions are important. Local infiltration of the region about the nerve with corticosteroids may be of value; in addition, surgical decompression may help if there is a progressively increasing neurologic deficit.
Ulnar Nerve Lesions
Ulnar nerve lesions are likely to occur in the elbow region as the nerve runs behind the medial epicondyle and descends into the cubital tunnel. In the condylar groove, the ulnar nerve is exposed to pressure or trauma. Moreover, any increase in the carrying angle of the elbow, whether congenital, degenerative, or traumatic, may cause excessive stretching of the nerve when the elbow is flexed. Ulnar nerve lesions may also result from thickening or distortion of the anatomic structures forming the cubital tunnel, and the resulting symptoms may also be aggravated by flexion of the elbow.
If conservative measures are unsuccessful in relieving symptoms and preventing further progression, surgical treatment may be necessary. This consists of nerve transposition if the lesion is in the condylar groove, or a release procedure if it is in the cubital tunnel..
Femoral Neuropathy
The clinical features of femoral nerve palsy consist of weakness and wasting of the quadriceps muscle, with sensory impairment over the anteromedian aspect of the thigh and sometimes also of the leg to the medial malleolus, and a depressed or absent knee jerk. Isolated femoral neuropathy may occur in diabetics.
Meralgia Paresthetica
The lateral femoral cutaneous nerve, a sensory nerve arising from the L2 and L3 roots, may be compressed or stretched in obese or diabetic patients and during pregnancy.
Sciatic & Common Peroneal Nerve Palsies
Misplaced deep intramuscular injections are probably still the most common cause of sciatic nerve palsy. Trauma to the buttock, hip, or thigh may also be responsible. The resulting clinical deficit depends on whether the whole nerve has been affected.
Tarsal Tunnel Syndrome
The tibial nerve, the other branch of the sciatic, supplies several muscles in the lower extremity, gives origin to the sural nerve, and then continues as the posterior tibial nerve to supply the plantar flexors of the foot and toes.
Facial Neuropathy
An isolated facial palsy may occur in patients with HIV seropositivity, sarcoidosis, or Lyme disease, but most often it is idiopathic (Bell's palsy).
3. Bell's Palsy
Bell's palsy is an idiopathic facial paresis of lower motor neuron type that has been attributed to an inflammatory reaction involving the facial nerve near the stylomastoid foramen.