Description

• Dysfunction of any region of the brachial plexus due to injury, lesion, or idiopathic etiologies
• The brachial plexus is a complex network of peripheral nerves arising from the lower neck that provide the sensory and motor innervation to the upper extremity.
• A brachial plexopathy should be considered in the differential diagnosis of any patient presenting with shoulder or upper extremity pain, weakness, or paresthesia.
• Brachial plexopathies are easy to confuse with cervical radiculopathies. Radiculopathies are usually sensorimotor dominate, and plexopathies are motor dominate and may have a decline in pain symptoms as motor weakness evolves.
• Clinical anatomy
  • The complex nerve network travels from the neck to the axilla before sending its terminal branches down the arm. In its course, it transverses through the anterior and middle scalene muscles, encircles the subclavian artery, and sends off several peripheral branches and nerves.
  • The brachial plexus arises from the ventral rami of spinal nerve roots C5–T1. The ventral rami travel distal and branch together to form the three main trunks (upper, middle, and lower). Fibers of the trunks then divide and reunite as they progress through the shoulder to form the cords (medial, lateral, and posterior). The cords then branch out to form the major nerves that supply motor and sensation to the upper extremity. The posterior cord forms the axillary and radial nerves. The lateral cord branches to form the musculocutaneous nerve and joins a branch of the medial cord to form the median nerve. The ulnar nerve arises from terminal end of the medial cord.
  • Some peripheral nerves of the brachial plexus arise directly from the ventral rami (long thoracic and dorsal scapular nerves) and some from the roots and cord levels (suprascapular, medial, and lateral pectorals; axillary, thoracodorsal, and lower subscapular).

Epidemiology

Incidence

• The most common etiology is traumatic.
• It is the most common peripheral nerve injury seen in athletes. It occurs at a rate as high as 49–61% of collegiate football players.
• Traumatic brachial plexopathy is more likely to occur in young athletes and males.
• Idiopathic brachial plexopathy (IBP), also known as Parsonage-Turner syndrome (PTS), brachial neuritis, or neuralgic amyotrophy, is rarer. It occurs with an overall incidence of 1.64 cases per 100,000. It occurs at all ages but is more common between the 3rd and 7th decades (1).

Etiology and Pathophysiology

• The pathologic basis can vary with the different etiologies: compression, transection, inflammatory, or idiopathic. However, the underlying mechanism can be traced to a dysfunction in nerve conduction: conduction block, failure, or slowing.
• Nerve compression or stretch may occur during contact sports; focal forces to the shoulder region result in brief compression of the ipsilateral plexus. Stretch of the shoulder and neck result in traction of the ipsilateral plexus or compression of the contralateral plexus. Nerve conduction returns to normal in matter of minutes or hours. An athlete may describe “shaking the arm out,” and this often referred to as a burner or a stinger (2).
• High-force trauma can cause a direct disruption of the nerve through transection from stretch or penetrating injury or it can injure the brachial plexus secondarily through disruption of blood supply or swelling around the brachial plexus (3).
• Idiopathic or PTS, the pathology may be autoimmune or inflammatory mediated. Up to 25% of nontraumatic brachial plexopathies have been linked to preceding infections, and up to 15% have been reported to occur following vaccinations. The majority of nontraumatic cases have no associated etiologies.
• Cancer-related brachial plexopathies; metastatic brachial plexopathies can result from compression by a lesion or invasion of cancer into the plexus or surrounding connective tissue. Radiation treatment for cancer can result in brachial plexus injury.