This is usually a complication of irradiation of the axilla for carcinoma of the breast. Stoll and Andrews studied a group of 117 such patients who were treated with high-voltage, small-field therapy and had received either 6,300 or 5,775 cGy in divided doses. Of those receiving the larger dose, 73 percent developed weakness and sensory loss in the hand and fingers between 4 and 30 months after treatment, most of them after 12 months. In 1 autopsied case, the brachial plexus was ensheathed in dense fibrous tissue; distal to this zone, both myelin and axons had disappeared (wallerian degeneration), presumably as a result of entrapment of nerves in fibrous tissue; possibly a vascular factor was also operative.
Kori and coworkers, who analyzed the brachial plexus lesions in 100 patients with cancer, also found that doses exceeding 6,000 cGy were associated with radiation damage. Usually the upper plexus was involved and was sometimes associated with a painless lymphedema. Myokymic discharges and fasciculations are particularly suggestive of radiation damage. In patients who received lower doses, the development of brachial plexopathy usually indicated tumor infiltration; these lesions affected the lower plexus more than the upper; they were often painful and accompanied by Horner syndrome (see Lederman and Wilbourn, 1984). Rarely, radiation may give rise many years later to a malignant tumor of nerve or the surrounding connective tissue, a sarcoma in 2 cases familiar to us.
Herpes Zoster Plexitis, Neuritis, and Ganglionitis (See Chap. 32)
This organism is perhaps the best defined infectious cause of the above listed syndromes, but its identification is usually obvious on the basis of the skin eruption of shingles. Cases are known in which radicular pain precedes the eruption by many days or in which shingles do not appear, thereby simulating a herniated disc (zoster sine herpete). These conditions are discussed with the other viral infections of the nervous system in Chap. 32.
This nerve is derived from the fifth, sixth, and seventh cervical nerves and supplies the serratus anterior muscle, which fixates the lateral scapula to the chest wall. Paralysis of this muscle results in an inability to raise the arm over the head and winging of the medial border of the scapula when the outstretched arm is pushed forward against resistance. The nerve is injured most commonly by carrying heavy weights on the shoulder or by strapping the shoulder to the operating table. As stated earlier, the neuropathy may be the only affected nerve in a brachial plexus neuropathy of either the inherited or idiopathic variety (Phillips).
This nerve is derived from the fifth (mainly) and sixth cervical nerves and supplies the supraspinatus and infraspinatus muscles. Lesions may be recognized by the presence of atrophy of these muscles and weakness of the first 15 degrees of abduction (supraspinatus) and of external rotation of the arm at the shoulder joint (infraspinatus). The latter muscle is tested by having the patient flex the forearm and then, pinning the elbow to the side, asking him to swing the forearm backward against resistance. This nerve is often involved as a result of a herniated C5-C6 disc (see Chap. 10), or as part of a brachial plexus neuropathy of either the sporadic or inherited type. It may be affected during infectious illnesses and may be injured in gymnasts, or as a result of local pressure from carrying heavy objects on the shoulder (“meatpacker’s neuropathy”). An entrapment syndrome has also been reported; it is characterized by pain and weakness on external rotation of the shoulder joint with atrophy of the infraspinatus muscle (Table 43-8). Decompression of the nerve where it enters the spinoglenoid notch relieves the condition.