The radial nerve is formed by axons from C5 to T1 roots and is branched off the lateral cord of the brachial plexus. Axons pass through several structures including the spiral groove of humerus, fibrous arch attachment of triceps to humerus, lateral intermuscular septum below deltoid insertion, and arcade of Frohse. Above the elbow, it branches off to innervate triceps, anconeus, brachioradialis, extensor carpi radialis longus/brevis, and posterior cutaneous nerves of the arm and forearm. At or below the elbow, branches are divided so that they come off either before or after the arcade of Frohse. Branches that come off the radial nerve before the arcade of Frohse include the superficial radial nerve, which supplies sensory innervation to dorsolateral hand and the first 31/2 digits, and the posterior interosseus nerve, which innervates the extensor carpi radialis brevis and supinator. Branches below the arcade of Frohse are the terminal motor branch of the posterior interosseus nerves, which innervate finger/thumb extensor, extensor carpi ulnaris, abductor pollicis longus, and articular branches to the wrist joint. Radial nerve injury is the least affected nerve among the three major nerves (median, ulnar, and radial) in the upper extremities. Radial nerve compression or injury may occur at any point along the anatomic course, ranging from proximally, involving brachial plexus, to distally, involving the radial aspect of the wrist, and may have varied causes (Table 110). The most frequent site of compression is in the proximal forearm in the area of the supinator muscle and involves the posterior interosseous branch.
Rupture, synovial effusion, compression, trauma, surgery, injection, and nerve tumor
a Pressure on medial arm compressing against humerus; often seen in sleep paralysis (Saturday night palsy), during anesthesia, and with tourniquet.
b Holstein-Lewis fracture, mid-third humerus fracture.
c Related to repetitive pronation-supination movement. Sometimes mistakenly referred to as “resistant tennis elbow.” Maximum tenderness located 4 to 5 cm distal to lateral epicondyle.
Plain x-ray can be obtained to rule out fracture, dislocation, bone tumor, and arthrosis. Magnetic resonance imaging (MRI) can be used to look for soft tissue lipoma, ganglioma, aneurysm, and synovitis. Electromyography (EMG) can also be really useful in determining the location, the timing (acute, subacute, or chronic), and the severity (demyelination or axon lost) of the nerve injury. However, EMG can be normal in the acute setting before Wallerian degeneration occurs, which usually takes about 3 to 7 days. High-resolution ultrasound evaluation of focal neuropathies may also be used in delineating nerve entrapment.
A period of immobilization and anti-inflammatory medication may diminish swelling and improve symptoms. In addition, functional splints help prevent contracture and improve function as signs of nerve healing follow. Surgical approach, especially for radial tunnel syndrome, is highly controversial. However, surgical approach would be warranted if the nerve injury is caused by structure compression (i.e., bone tumor, lipoma).
Radiation injury to the nervous system occurs either as a result of treatment of CNS tumors, when nervous tissue falls into the field of treatment of another organ system or exposure to radiation accidentally, or in warfare. Radiation can damage the cerebral cortex, spinal cord, peripheral nerves, and cerebrovascular system and induce new tumors.
Radiation plexopathy of the brachial or lumbosacral plexi must be distinguished from recurrent tumor in neighboring structures such as breast or lung. Radiation plexopathy tends to produce less pain but more weakness than tumor invasion. Paresthesias and edema are common. EMG may show myokymic discharges. Contrast-enhanced CT, MRI, and PET often help in differentiating radiation plexopathy from other compressive lesions.
Extracranial carotid disease, with transient ischemic attacks or strokes, may develop 6 months to 50 years (median, 10 to 20 years) after radiation therapy for head and neck cancers. Vascular studies show disease limited to the field of radiation, including such unusual sites as proximal common carotid artery and internal carotid artery distal to the common carotid bifurcation. Occlusive disease of the intracranial arteries may follow irradiation of optic gliomas, pituitary, or suprasellar tumors (2 to 20 years later; median, 5 years). The most frequent finding on arteriography is narrowing or occlusion of the supraclinoid internal carotid artery and proximal middle cerebral artery. Vasculopathy following radiation therapy in early childhood (usually for suprasellar tumors) frequently shows a “moyamoya” pattern. Radiation-induced stenosis is better treated with stenting than open surgery.
In order of decreasing frequency, meningiomas, gliomas, and sarcomas may occur after radiation therapy. Meningiomas have a latency of 15 to 50 years (mean, 36 years) after irradiation, and gliomas may develop approximately 10 years after irradiation.
Radiculopathy is the result of any process that causes damage to or irritation of the nerve root. The spinal roots may be injured by compression (disk disease, spondylosis, hypertrophied ligaments, epidural abscess), trauma, or nondegenerative causes such as diabetes, vasculitis, tumor, infection (i.e., herpes zoster and Lyme disease), and demyelination. Cervical and lumbosacral regions are the two most commonly involved areas.
Radiculopathy presents as radicular pain. Radicular pain is characteristically lancinating, electrical, burning, abrupt, referred to a particular dermatome, and aggravated by maneuvers that stretch the dorsal nerve root, such as coughing or sneezing, or the Valsalva maneuver. There may be sensory changes and weakness in the affected dermatome and myotome, respectively. Exam findings comprise hypesthesia or anesthesia confined to the involved dermatome; due to overlap of cutaneous innervation, there may be little or no sensory loss on exam. Weakness may occur in the appropriate myotomal distribution. Fasciculations may be present. Hyporeflexia or areflexia are restricted to the muscles supplied by the involved root (Table 111). Straight leg raising sign and Spurling sign (limb pain or paresthesia following extension and rotation of the neck to the side of the pain) may be present in cases of lumbar and cervical radiculopathy, respectively. Crossed straight leg raising usually indicates a larger lesion. Improvement of the radicular symptoms with shoulder abduction may also be present in cervical radiculopathy (shoulder abduction relief test). Central lumbar lesions may result in cauda equina syndrome or conus lesion (Table 112).