In this case, the entire arm is paralyzed and hangs uselessly at the side; the sensory loss is complete below a line extending from the shoulder diagonally downward and medially to the middle third of the upper arm. Biceps, triceps, radial, and finger reflexes are abolished. The usual cause is vehicular trauma, especially motorcycle injury.
This is a result of injury to the distal fifth and sixth cervical roots, the most common causes of which are forceful separation of the head and shoulder during difficult delivery, pressure on the supraclavicular region during anesthesia, immune reactions to injections of foreign serum or vaccines, and idiopathic brachial plexitis (see later). The muscles affected are the biceps, deltoid, supinator longus, supraspinatus and infraspinatus, and, if the lesion is very proximal, the rhomboids. The arm hangs at the side, internally rotated and extended at the elbow. Movements of the hand and forearm are unaffected. The prognosis for spontaneous recovery is generally good, although this may be incomplete. Injuries of the upper brachial plexus and spinal roots incurred at birth (termed in older literature as Erb-Duchenne palsy) usually persist throughout life.
This is commonly the result of traction on the abducted arm in a fall or during an operation on the axilla, infiltration or compression by tumors extending from the apex of the lung (superior sulcus or Pancoast syndrome), or compression by cervical ribs or bands. Injury may occur during birth, particularly with breech deliveries (termed Dejerine-Klumpke paralysis). There is weakness and wasting of the small muscles of the hand and a characteristic clawhand deformity. Sensory loss is limited to the ulnar border of the hand and the inner forearm; if the first thoracic motor root is involved, there may be an associated paralysis of the cervical sympathetic nerves with a Horner syndrome. Invasion of the lower plexus by tumors is usually painful; postradiation lesions are more likely to cause paresthesias without pain (Lederman and Wilbourn, 1984).
Infraclavicular Lesions Involving Cords of the Brachial Plexus (See Fig. 43-5)
A lesion of the lateral cord causes weakness of the muscles supplied by the musculocutaneous nerve and the lateral root of the median nerve; it manifests mainly as a weakness of flexion and pronation of the forearm. The intrinsic muscles of the hand innervated by the medial root of the median nerve are spared. A lesion of the medial cord of the plexus causes weakness of muscles supplied by the medial root of the median nerve and the ulnar nerve. The effect is that of a combined median and ulnar nerve palsy. A lesion of the posterior cord results in weakness of the deltoid muscle, extensors of the elbow, wrist, and fingers, and sensory loss on the outer surface of the upper arm.
One group of infraclavicular injuries, often iatrogenic, results from damage to the subclavian or axillary vessels and the formation of pseudoaneurysms or hematomas. Small puncture wounds—as might occur with catheterization of the subclavian vein, anesthetic block of the brachial plexus, or transaxillary arteriography—are likely to produce this type of injury. As mentioned earlier, thrombosis of the vessels of the neurovascular subclavian bundle are a rare cause. Other frequent causes of injury to the cords are dislocation of the head of the humerus, direct axillary trauma (stab wounds), and supraclavicular compression during awkward positioning of the arm in an operation. Any cords of the plexus may be injured or they may be affected in various combinations.
This subject is discussed extensively in Chap. 10.
Brachial Neuritis, Brachial Plexitis (Neuralgic Amyotrophy, Parsonage-Turner Syndrome)