What are the causes and clinical features of brachial plexopathy?

Causes and Clinical Features of Brachial Plexopathy

Brachial plexopathy has multiple etiologies including traumatic, neoplastic, inflammatory/immune-mediated, radiation-induced, diabetic, vascular, infectious, hereditary, and idiopathic causes, with distinct clinical presentations characterized by pain, weakness, and sensory loss across multiple peripheral nerve distributions in the shoulder and arm. 1, 2

Anatomical Context

• The brachial plexus is formed from the ventral rami of C5-T1 nerve roots, with occasional contributions from C4 and/or T2, passing between the anterior and middle scalene muscles alongside the subclavian artery 2, 3
• The plexus is organized sequentially into roots, trunks, divisions, cords, and terminal branches that supply the upper extremity 3
• Understanding this complex anatomy is crucial for accurate diagnosis and treatment planning of plexopathies 3

Causes of Brachial Plexopathy

Neoplastic Causes

• Primary tumors of the brachial plexus are most commonly benign peripheral nerve sheath tumors (schwannomas and neurofibromas) 1
• Malignant peripheral nerve sheath tumors are rare and occur more frequently in patients with neurofibromatosis type 1 1
• Non-neurogenic primary tumors include desmoid tumors and lipomas 1
• Secondary involvement occurs through direct invasion or metastasis from adjacent tumors, most commonly lung cancer (Pancoast tumors) and breast cancer 1, 3
• Lymphoma can involve the plexus through local encasement or nerve infiltration 1

Inflammatory/Immune-Mediated Causes

• Parsonage-Turner syndrome (neuralgic amyotrophy or brachial plexitis) is characterized by acute onset of pain followed by weakness 1, 3
• Chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) can present with brachial plexopathy 1, 4
• Other inflammatory neuropathies include multifocal motor neuropathy and Lewis-Sumner syndrome 1

Traumatic Causes

• Trauma may result from direct blunt force, penetrating injuries, or traction/stretch injuries 5
• Can be classified as preganglionic (root avulsion) or postganglionic injuries 4
• Iatrogenic injuries can occur during surgical procedures 6

Other Causes

• Hereditary neuropathies (e.g., Charcot-Marie-Tooth syndrome, hereditary neuralgic amyotrophy) 1, 5
• Neurogenic thoracic outlet syndrome affecting the lower trunk 5
• Radiation-induced plexopathy as a delayed complication of radiation therapy 4
• Infectious causes 1
• Idiopathic brachial neuritis, which may or may not be preceded by antecedent events such as infection 5, 7

Clinical Features

Pain Characteristics

• Neuropathic pain occurs across multiple peripheral nerve distributions in the shoulder and arm 2
• Pain distribution crosses multiple dermatomes, distinguishing it from radiculopathy 2
• In Parsonage-Turner syndrome, severe pain often precedes weakness, though interestingly, 47% of patients with brachial neuritis may not experience pain before onset 7

Motor Symptoms

• Weakness occurs in regions innervated by multiple nerves from the affected plexus 2
• Complete plexopathy causes flaccid weakness in the distribution of multiple peripheral nerves 2
• Upper trunk involvement (most common at 27% of cases) affects shoulder abduction and external rotation, elbow flexion, and forearm supination 7
• Lower trunk involvement (11% of cases) affects intrinsic hand muscles and ulnar-innervated muscles 7

Sensory Symptoms

• Sensory loss occurs across multiple nerve distributions 2
• The pattern of sensory loss helps localize the lesion within the plexus 8

Reflex Changes

• Flaccid loss of tendon reflexes occurs in regions innervated by the affected plexus 2
• Biceps and brachioradialis reflexes are affected in upper trunk lesions, while triceps reflex is affected in middle trunk lesions 8

Diagnostic Approach

• Clinical diagnosis is confirmed by electrodiagnostic studies showing abnormalities in multiple nerve distributions 2, 8
• MRI of the brachial plexus is the imaging modality of choice due to its superior soft-tissue contrast and spatial resolution 1
• CT with IV contrast can be useful when MRI is contraindicated, offering the next highest level of anatomic visualization 1
• It is essential to differentiate plexopathies from radiculopathies, which typically follow a single dermatome distribution 4

Common Pitfalls in Diagnosis

• Symptoms of brachial plexopathy are often nonlocalizing, making diagnosis challenging 9
• Failure to recognize the involvement pattern may lead to misdiagnosis 7
• In brachial neuritis, the absence of pain (47% of cases) and antecedent viral illness (only 28% have a definable antecedent illness) is more common than typically described 7
• Distinguishing between preganglionic and postganglionic lesions is crucial as treatment approaches differ 3