Definition

Brachial plexopathy is the pathologic dysfunction of the brachial plexus, a complex peripheral nerve structure in the proximal upper extremity. The brachial plexus starts just outside the spinal cord in the lower neck and extends to the axilla. The total average brachial plexus length is approximately 6 inches [1]. The plexus is divided into five sections: roots, trunks, divisions, cords, and branches or terminal nerves. The spinal nerves C5 through T1 classically supply anterior primary rami of the nerve roots, which then form the plexus. Variations in nerve root supply that involve other nerve roots are said to be expanded. When the C4 nerve root also supplies the brachial plexus and T1 contribution is minimal, the plexus is called prefixed. When the T2 nerve root supplies the brachial plexus and C5 contribution is minimal, the plexus is said to be postfixed [2]. The nerve roots combine to form the trunks behind the clavicle. There are three trunks, the upper, middle, and lower. The upper is formed from the C5 and C6 nerve roots, the middle is a continuation of C7, and the lower is formed from C8 and T1. The trunks then divide behind the clavicle into anterior and posterior divisions. Just inferior to the clavicle, the divisions coalesce into cords. The cords travel along the axillary artery, just inferior to the clavicle, and are named for their spatial relationship to the artery. The posterior cord is formed from the union of the three posterior divisions. The lateral cord is formed by the union of the anterior divisions of the upper and middle trunks. The medial cord is the continuation of the anterior division of the lower trunk. Nerve branches are the most distal elements of the brachial plexus and are the major nerves of the upper extremity. These branches begin in the distal axilla and other than the median nerve, which is formed by contributions from the medial and lateral cords, are continuations of the cords. There are also numerous peripheral nerves that arise directly from the roots, trunks, and cords (Fig. 143.1).

Brachial plexopathy can be due to wide-ranging causes, including idiopathic, iatrogenic, autoimmune, traumatic, neoplastic, and hereditary. It can occur in any age group; but other than when it is secondary to obstetric trauma, it usually occurs from the ages of 30 to 70 years. Men are affected two to three times as often as are women, and the reason is likely due to their more frequent participation in vigorous athletic activities that can lead to trauma. About half of the cases have no identified precipitating event; in others, brachial plexopathy follows an antecedent infection, trauma, surgery, or immunization.

Symptoms

Brachial plexopathy can result in symptoms of pain, weakness, and numbness, both at the level of the brachial plexus and distally in the supplied upper extremity. The area of pain and other symptoms correlates with the portion of the brachial plexus involved and the specific nerve elements from that area. Depending on the cause of the plexopathy, symptom onset can range from sudden to insidious. Because of the complex muscle suspension of the shoulder joint, chronic brachial plexopathy may result in glenohumeral subluxation and instability due to stretching of the shoulder capsule. Brachial plexopathy usually does not cause prominent neck pain. Some brachial plexopathies may occur bilaterally and therefore cause symptoms in both upper extremities.

Physical Examination

The physical examination of the brachial plexus for brachial plexopathy must be thorough because of the complexity of its structure and function. The shoulder girdle and entire extremity need to be exposed during examination to allow close inspection of muscle bulk and fasciculations. Assessment of atrophy of muscles is often assisted by side-to-side comparisons. Muscle strength examination needs to be thorough and to include proximal muscles not commonly tested, such as infraspinatus, supraspinatus, rhomboids, and serratus anterior. Sensory testing also must be thorough, with both dermatomal and peripheral nerve sensory distributions examined. A musculoskeletal examination of the shoulder joint is helpful; joint disease can be both a possible primary cause of pain and a secondary effect of plexopathy. Shoulder range of motion and signs of tendinosis as well as reflexes and any muscle atrophy need to be assessed. The lack of pain exacerbation with neck movement and multiroot distribution of sensory or motor deficits can help distinguish brachial plexopathy from cervical radiculopathy, which more commonly affects a single root [3]. It is often not possible to determine the exact location of a brachial plexus lesion from physical examination, but the examination is usually helpful in focusing electrodiagnostic and radiologic testing.

Functional Limitations

Depending on whether the brachial plexopathy involves the upper plexus, lower plexus, or entire plexus, the proximal shoulder muscles, the distal muscles involved in fine finger movements, or the entire extremity can be weak or numb. Activities of daily living, such as dressing, feeding, and grooming, can be significantly affected. These impairments can result in disabilities in many activities, including computer use, writing, and driving. Brachial plexopathy secondary to birth trauma may subsequently cause difficulty for children and teens with sports and other recreational activity.

Diagnostic Studies

Electromyography (EMG) can be helpful in localizing the pathologic area in brachial plexopathy as well as in determining the severity of axonal injury and the potential for recovery. However, many brachial plexopathies cannot be definitely localized by EMG because of subtle findings encountered with incomplete nerve injury and the complexity of plexus-related innervation. The nerve conduction and needle EMG assessment is best directed by both symptoms and physical examination findings. Both nerve conduction studies and needle EMG are required for complete assessment. Sensory nerve conduction studies can help in localization by the pattern of abnormalities seen and in judging injury severity based on reductions of amplitudes or absence of potentials. The nerve conduction study may not detect abnormality if the lesion is mild in severity or too recent to allow axonal degeneration.

The following five basic sensory nerve conduction studies are suggested as a screen for brachial plexus evaluation: lateral antebrachial cutaneous, median recording from the thumb, median recording from the index finger, superficial radial, and ulnar recording from the little finger [2]. The presence of fibrillation potentials in EMG is particularly sensitive for motor axon loss and helps localize the site of lesions. The choice of muscles sampled on EMG is usually focused on the area of interest, but other areas are also included for the exclusion of wider disease. It is important to include paraspinal muscles of the relevant areas to investigate the possibility of radiculopathy (paraspinals are supplied by the posterior primary rami of the nerve roots, which do not supply the brachial plexus). EMG evaluation of the brachial plexus is complex and best performed by experienced electromyographers.

Radiologic studies of the plexus are helpful to evaluate the severity of trauma, presence of mass lesions, and inflammation of the brachial plexus nerve elements [4