Brachial Plexopathy

01Anatomy and electrodiagnostic evaluation

• The plexus is formed by ventral rami of the lower cervical and upper thoracic roots. Fibers from these roots intermingle before contributing to the peripheral nerves of the upper extremity.
• NCS and needle EMG help localize a suspected lesion and assess severity. The evaluation is demanding, often requiring extensive bilateral studies with particular attention to sensory conduction and needle EMG.
• Precise localization helps distinguish plexopathy from clinically similar root disease and may suggest an etiology because some disorders favor particular plexus segments. Severity assessment is especially relevant in trauma when considering surgery. Much of the plexus lies beneath or inferior to the clavicle, limiting ultrasound access, though ultrasound can help with selected disorders.

02Panplexus lesion

• A complete plexopathy causes weakness and sensory loss throughout the arm, with reduced or absent reflexes. If the roots remain intact, the serratus anterior and rhomboids are usually the only muscles spared because their nerves arise directly from the roots, proximal to the plexus.
• Clinical and needle EMG assessment of these muscles helps distinguish a severe plexus lesion from a root lesion.

03Trunk localization

• Upper trunk (C5–C6): weakness is greatest in the deltoid, biceps, brachioradialis, supraspinatus and infraspinatus; pronator teres and triceps may be partly affected. Sensory loss can involve the lateral arm, forearm and hand and the thumb. Biceps and brachioradialis reflexes are reduced or absent, with the triceps reflex spared.
• Middle trunk (C7) lesions are rare and can mimic C7 radiculopathy. Weakness mainly affects triceps, flexor carpi radialis and pronator teres; sensory changes predominate in the middle finger and posterior forearm. The triceps reflex is abnormal.
• Lower trunk (C8–T1): weakness affects ulnar muscles, C8–T1 median muscles (e.g., abductor pollicis brevis, flexor pollicis longus and flexor digitorum profundus), and C8 radial muscles (e.g., extensor indicis proprius and extensor pollicis brevis). Sensory loss can involve the medial arm, forearm and hand and the fourth and fifth fingers. Pure lower-trunk lesions do not alter reflexes.

04Cord localization

• Lateral cord: musculocutaneous and C6–C7 median fibers are affected, causing weakness of elbow flexion, pronation and wrist flexion. Sensory changes involve the lateral forearm and hand and first three fingers. The biceps reflex is abnormal; triceps and brachioradialis reflexes are preserved.
• Posterior cord: radial, axillary and thoracodorsal nerves are affected. A radial palsy with wrist and finger drop may occur alongside weak shoulder abduction and adduction. Sensory loss can involve the lateral and posterior arm, posterior forearm and radial dorsal hand; triceps and brachioradialis reflexes are abnormal.
• Medial cord: the pattern resembles a lower-trunk lesion, but radial C8 fibers are spared. Ulnar and C8–T1 median muscles are affected, while finger extensors—especially those to the index finger—are spared. Sensory loss resembles the lower-trunk pattern.

05Traumatic plexopathy

• Trauma is the most common cause; settings include vehicle crashes, penetrating wounds and traction during childbirth. Head traction away from the shoulder typically injures the C5–C6 upper trunk, causing Erb palsy with weak shoulder abduction, elbow flexion and supination. Shoulder dystocia, especially in a large infant, is a major neonatal risk factor.
• Upward traction on the arm and shoulder typically injures C8–T1 lower-trunk fibers, causing Klumpke palsy: severe hand weakness with relative sparing of the upper arm and shoulder girdle.
• Severe traction can also injure roots. Root avulsion separates roots from the spinal cord and is the most severe injury, described in the source as having no chance of recovery. NCS and needle EMG help distinguish root avulsion, plexus injury and combined lesions.

06Neoplasms and other masses

• Tumors may directly invade the plexus (e.g., Pancoast tumor) or compress it through metastatic lymph nodes. Lymphoma, breast cancer and lung cancer are frequent causes; lymphoma and leukemia can also infiltrate nerves without a mass. Rare causes include nerve-sheath tumors, hematomas and vascular lesions such as aneurysms or arteriovenous malformations.
• Neoplastic plexopathy is often painful and slowly progressive and may resemble cervical root disease. Electrodiagnostic testing can help distinguish the two.

07Neuralgic amyotrophy

• Neuralgic amyotrophy (NA; Parsonage–Turner syndrome or brachial neuritis) more often affects individual upper-extremity nerves than the plexus as a whole, making it an acute mononeuropathy multiplex. Some cases affect the plexus directly; root involvement is rare. Viral illness, immunization, surgery, trauma or unusual muscular effort may precede onset, and hepatitis E has a strong reported association.
• Severe shoulder pain typically begins days to weeks after a trigger, may resist analgesics and can wake the patient. Weakness becomes clearer as pain subsides, often after one to two weeks, followed by atrophy. Sensory changes are often mild. Commonly affected nerves, in reported order, are suprascapular, long thoracic, anterior interosseous, axillary, musculocutaneous, posterior interosseous and radial. Long thoracic palsy causes scapular winging; anterior interosseous palsy weakens thumb and index-finger flexion and can impair the OK sign.
• NA may favor nerves without cutaneous sensory fibers, making sensory NCS less informative despite deep pain and muscle afferents. Phrenic involvement occurs; lower cranial neuropathies are rare. Episodes are usually unilateral and often occur once, though needle EMG may show contralateral abnormalities. Recurrence raises concern for hereditary SEPT9-related NA. Proposed contributors include immune or environmental triggers, mechanical stress and genetic susceptibility.

08Postoperative plexopathy

• After coronary artery bypass and similar chest operations, stretch from chest-wall retraction or compression from an internal-jugular-catheter hematoma may injure the plexus. Lesions nearly always predominantly affect the lower trunk or medial cord.
• The usual pattern is C8–T1 sensory disturbance in the fourth and fifth fingers, sometimes extending along the medial forearm and arm, with weakness in C8–T1 muscles: hand intrinsics, long finger flexors and, less prominently, finger extensors to the thumb and index finger. Recovery over several months is common, but incomplete recovery and chronic pain can occur.

09Delayed radiation injury

• Radiation plexopathy may progress years after treatment; risk rises with dose, and the excerpt notes greater frequency above 5,700 rads. Recurrent tumor invasion is a key alternative in a patient with prior cancer.
• Earlier, prominent pain and Horner syndrome favor direct tumor invasion. Paresthesias and numbness often appear earlier with radiation injury, and symptoms may persist for years before evaluation.
• Myokymic discharges on needle EMG are characteristic of radiation plexopathy; fasciculations may also help. Conduction block is nonspecific, and the plexus region involved or clinical weakness generally does not distinguish radiation from tumor.

010Thoracic outlet syndrome

• True neurogenic thoracic outlet syndrome (TOS) is rare; many historical diagnoses were more likely cervical radiculopathy, ulnar neuropathy at the elbow or median neuropathy at the wrist. Most true cases are attributed to a fibrous band from a rudimentary cervical rib to the first rib, compressing the lower trunk, often preferentially affecting T1 fibers.
• The pattern is C8–T1 weakness and sensory loss, often with thenar wasting greater than hypothenar wasting. Long finger and thumb flexors may be affected; radial C8 weakness is less common. Sensory symptoms involve the fourth and fifth fingers, medial hand and medial forearm.
• Neck pain radiating down the arm and provoked by neck movement favors radiculopathy; local elbow tenderness favors ulnar neuropathy. Thumb abduction is usually spared in ulnar neuropathy but may be disproportionately weak in TOS. Medial-forearm sensory changes can occur in TOS or C8–T1 radiculopathy, but are not typical of ulnar neuropathy at the elbow.

Related nerves

Pause and explain

Explain in your own words: “Combine sensory territories, muscles supplied by different terminal nerves, reflexes and time course to localize the lesion before assessing its cause and severity.” Then think of a situation in which it could be misinterpreted.

References and further reading

• Neuroanatomy for Nerve Conduction Studies (2017) ↗AANEM · Anatomy course · Link accessed 2026-09-08
• Brachial Plexopathy: Differential Diagnosis and Treatment ↗AAPM&R KnowledgeNow · Society educational review · Link accessed 2026-09-08
• Electrodiagnosis of Radiculopathies ↗AAPM&R KnowledgeNow · Society educational review · Link accessed 2026-09-08
• Immune Mediated Brachial Plexopathy ↗AAPM&R KnowledgeNow · Society educational review · Link accessed 2026-09-08
• Radiation Induced Plexopathy ↗AAPM&R KnowledgeNow · Society educational review · Link accessed 2026-09-08

Educational synthesis; independent neuromuscular specialist review is pending. Publication dates and compilation dates are distinct. This is an original teaching synthesis; consult the source for complete methods and criteria.