Pain. Pain descriptions are never pathognomonic of specific disorders. Tingling or radiating pain suggests a peripheral nerve, plexus, or root disorder, whereas dull, aching, nonradiating pain is typical of MSK disorders. Exceptions to this rule occur frequently. Acute onset of excruciating pain in the shoulder or arm is common with idiopathic brachial plexopathy. Pain radiating from the neck to the arm or hand suggests radiculopathy. The pain location may suggest the root involved—for example, lateral arm (C5), lateral forearm or thumb (C6), middle finger (C7), or medial hand and forearm (C8). Pain localized to the shoulder may result from MSK disorders, such as bicipital tendinitis, rotator cuff injury, and adhesive capsulitis, or from PNS disorders, such as C5 radiculopathy, brachial plexopathy, or entrapment of the suprascapular or dorsal scapular nerves (DSNs). Pain radiating distant from the site of pathology may belie the location—for example, carpal tunnel syndrome (CTS) occasionally manifests as forearm or shoulder pain. Forearm pain may occur with C6 radiculopathy, plexopathy, or nerve entrapment in the forearm. Pain involving specific digits may help localization. Pain involving the thumb, index finger, or middle finger suggests a median mononeuropathy, a C6 or C7 radiculopathy, or middle brachial plexus disorder. Pain involving the ring and little fingers suggests an ulnar mononeuropathy, a lower plexus disorder, or C8-T1 radiculopathy. Digital pain may also result from local MSK disorders—for example, arthritis. Bizarre descriptions of pain are typical of psychological or functional disorders.

Paresthesias and sensory loss. Paresthesias are spontaneous sensations originating from nerve fibers, which patients describe as “tingling” or “pins and needles.” Sensory loss indicates absence of normal sensation, which patients may describe as “numbness” or “like Novocain.” Paresthesias and sensory loss may occur together or independently, and either suggests that PNS disease is more likely than an MSK disorder. The distribution of paresthesias or sensory loss helps localize a nerve disorder. However, patients may report a distribution of sensory symptoms that varies from the precise anatomic distribution of an affected nerve or nerve root. Patients with CTS may complain of sensory symptoms in any of the first three hand digits and often report the entire hand is numb. Thus, failure of sensory symptoms to localize precisely to a specific nerve or nerve-root distribution should not exclude these disorders. The differential diagnosis of paresthesias and sensory loss should include CNS disease, especially when pain is absent. Intermittent paresthesias also occur in normal individuals, usually related to a specific activity or limb position resulting in nerve compression, stretch, or irritation. Thus, paresthesias in isolation do not always indicate a pathologic state

Motor vehicle accident (MVA). The severe trauma of a MVA may cause multiple neurologic complications including vertebral fracture with direct spinal cord injury, nerve-root avulsion, radiculopathy, brachial plexus injury, peripheral nerve injury, or late development of syringomyelia. Arm traction or stretching the arm and neck in opposite directions may cause cervical root avulsions or a stretch injury to the brachial plexus. An MVA may cause more than one PNS disorder—for example, cervical nerve-root avulsions and concomitant peripheral nerve injury. After an MVA, attention to multiple life-threatening injuries, or casting for multiple limb fractures, may preclude detection of PNS disorders until late in the course of recovery.

Fractures and dislocations may cause specific nerve injuries. Shoulder dislocation or fracture of the humerus may injure the axillary nerve. Fracture of the clavicle may injure components of the brachial plexus. Fracture of the humerus predisposes to radial nerve injury in the spiral groove, whereas fracture or dislocation of the radius may injure the posterior interosseous nerve (PIN) branch of the radial nerve. Fracture of the elbow predisposes to ulnar mononeuropathy, which may not manifest until years after the trauma, hence the name “tardy ulnar palsy.” A wrist fracture may cause either median or ulnar mononeuropathy.

Laceration. When UE pain or sensorimotor symptoms begin after a skin laceration or puncture wound, direct injury to a nerve needs to be considered. Exploration is needed to determine if the nerve requires repair.

Endocrine disorders. Patients with diabetic polyneuropathy are more vulnerable to development of mononeuropathies at physiologic compression sites. Patients with hypothyroidism are prone to developing CTS.

Rheumatologic disorders. Several rheumatologic disorders predispose to UE nerve or nerve-root injury. Rheumatoid arthritis causes joint and degenerative bone disease that may lead to cervical radiculopathy, CTS, and PIN injury. Systemic vasculitis may involve individual peripheral nerves in either the upper or lower extremities. Abrupt onset of a mononeuropathy is occasionally the presenting manifestation of systemic vasculitis. Primary and hereditary amyloidosis are associated with CTS.

Renal failure and dialysis. Patients receiving chronic hemodialysis are particularly likely to develop CTS, owing to the deposition of amyloid material (ß-2 microglobulin) within the carpal tunnel. Placement of arteriovenous fistulas for hemodialysis may cause median or ulnar neuropathies and, less often, a severe distal ischemic injury to all UE nerves, called ischemic monomelic neuropathy. Diabetic patients seem particularly prone to this severe nerve injury.

Malignancy. A patient with a history of cancer—particularly of the breast or lung—who develops UE sensorimotor complaints needs to be evaluated for metastases to the brachial plexus. Patients with radiation therapy to the brachial plexus region can develop radiation-induced brachial plexopathy, which may begin many years after radiation therapy.