Brachial Plexopathies

Brachial plexopathies encompass conditions that cause compression or dysfunction of the brachial plexus, resulting in neuropathic symptoms in the upper extremity. Common etiologies include thoracic outlet syndrome, Parsonage-Turner syndrome, and transient traumatic neuropraxia. Other causes include hereditary brachial plexopathy, radiation, malignancy, and iatrogenic injuries (Table 1). Table 1. - A noncomprehensive list of documented brachial plexopathies. Brachial Plexopathies Common Etiologies Other Focal Etiologies Systemic Etiologies Neurogenic thoracic outlet syndrome Erb-Duchenne palsy Thalamic pain syndrome Parsonage-Turner syndrome Klumpke Palsy Focal sensory seizures Transient traumatic neuropraxia Hereditary neuralgic amyotrophy Multiple Sclerosis Neoplasm (Pancoast syndrome) Herpes zoster Diabetic-related brachial plexopathy Mononeuritis multiplex Rucksack palsy Paget-Schroetter disease Traumatic nerve root avulsion Hemiplegic migraine Iatrogenic plexopathies Multifocal motor neuropathy Adapted from Smith et al. (1). Thoracic Outlet Syndrome Definition A heterogeneous group of disorders characterized by compression of neurovascular structures of the thoracic outlet (the anatomic window in the lower neck between the thorax and axilla). Compression of the brachial plexus resulting in neuropathic symptoms is known as neurogenic thoracic outlet syndrome (TOS). Occlusion of the axillary/subclavian artery or vein leading to signs and symptoms of ischemia or venous stasis corresponds to arterial or venous forms of TOS (2,3). Pathophysiology Neurogenic TOS is commonly caused by compression of the brachial plexus within the interscalene triangle (anterior scalene, middle scalene, and first rib). Compression also may occur within the costoclavicular space or the coracopectoral tunnel (coracoid process, pectoralis minor, ribs 2–4) (Fig. 1). Anatomic variants (cervical ribs), tumors, soft tissue masses, and muscular hypertrophy also can cause neurogenic TOS (3,4). Higher risk activities include swimming, baseball, rowing, weightlifting, water polo, and volleyball (4).Figure 1.: Thoracic outlet anatomy — dotted lines delineate the three anatomical spaces within the thoracic outline. Triangle — interscalene triangle; rectangle — costoclavicular space; circle — corocopectoral tunnel. Reprinted with permission from (5). ASM, anterior scalene muscle; MSM, middle scalene muscle; PMM, pectoralis minor muscle; PSM, posterior scalene muscle; SA, subclavian artery; SCM, subclavius muscle; SV, subclavian vein.Clinical Features Patients present with pain, paresthesia, weakness, or atrophy in the upper extremity that is provoked by overhead movements. The Gilliat-Sumner hand sign is atrophy of the abductor pollicis brevis, interosseous, and abductor digiti minimi muscles (6). Adson’s test and Roos test are commonly performed in combination in clinical practice, yielding a sensitivity and specificity of 84% to 98% and 82%, respectively. Other exam maneuvers include Cyriax release, Eden’s, and brachial plexus compression (2–4). Diagnostics Radiographs can detect osseous abnormalities such as cervical ribs or elongated transverse processes. Ultrasound may show compressive lesions or abnormalities in the scalene musculature of the brachial plexus. Magnetic resonance imaging (MRI) may show brachial plexus edema and denervation changes in affected muscles. Electrodiagnostic studies can be considered for persistent neuropathic symptoms, though they are often normal (7,8). Diagnostic lidocaine injections into the anterior scalene muscle also have been described (2,4,7,8). Management Conservative therapy includes nonsteroidal anti-inflammatory drugs, weight loss, and disease-specific physical therapy of the periscapular, scalene, and pectoralis minor muscles. Nerve gliding and postural correction also can improve symptoms. Injection therapy with lidocaine, steroid, or Botulinum toxin into the anterior scalene muscle can be considered (7). Surgery is recommended to correct anatomic abnormalities in patients who fail conservative treatment (4). Parsonage-Turner Syndrome (Neuralgic Amyotrophy, Idiopathic Brachial Plexus Neuropathy, and Brachial Neuritis) Definition Acute, idiopathic, rapid-onset neuropathic syndrome of the brachial plexus resulting in severe upper extremity pain, paresis, and proximal muscular atrophy (9,10). Pathophysiology Immune-mediated mechanism leading to the formation of cross-reactive antibodies or T cells. Common triggers include infection, vaccination reaction, immunotherapy, surgery, pregnancy, mechanical stress, or psychological distress (9,11). Common infectious etiologies include Hepatitis E, Coxsackie B, CMV, COVID-19, Dengue, Influenza A, and Parvovirus, along with reports of several postvaccine triggers (9,11). Clinical Features Acute onset of constant, sharp, stabbing unilateral shoulder pain that transitions to a deep ache predominantly occurring at night (9,11). Pain episodes generally last from days to weeks (11). Paresis develops within days to weeks after onset of pain, resulting in severe weakness and atrophy (11). The upper and middle trunks of the brachial plexus are typically affected. While any nerve within the plexus can be involved, the suprascapular nerve (58%), long thoracic nerve (30%–70%), axillary nerve (25%) and musculocutaneous nerve (15%) are more commonly affected (9,11). Diagnostics Primarily a clinical diagnosis. Electrodiagnostic studies may help determine prognosis. MRI may show hourglass swellings and constrictions of affected nerves (9,11). Management Early initiation of systemic corticosteroids may provide pain relief and shorten work incapacity lengths (9). Gabapentinoids and nonsteroidal anti-inflammatory drugs may also improve symptoms. Exercise programs for rotator cuff and scapular stability are recommended (9,11,12). Most patients begin to improve after 1 month from symptom onset, and 80% recover within 2 to 3 years (9,12). Severe or refractory cases may warrant referral for surgical decompression (9). Transient Traumatic Neuropraxia Definition Traction injury to the brachial plexus, typically sustained during contact sports, also known as stingers or burners (13–15). Pathophysiology Peripheral nerve injury to the brachial plexus myelin sheath (most commonly the C5–C6 nerve root) resulting in demyelination but with axonal preservation (Seddon grade I; Table 2) (16,17). The typical mechanism is lateral neck flexion and shoulder depression (13,18). Table 2. - Seddon classification is graded in 3 forms: neuropraxia, axonotmesis, and neurotmesis. Seddon Classification Seddon Type Myelin intact Endoneurium Wallerian Degeneration Reversibility Neuropraxia Grade I No Intact No Reversible Axonotmesis Grade II No Variable Yes Variable Neurotmesis Grade III No Transected Yes Irreversible Transient traumatic neuropraxia falls into grade 1 under neuropraxia where there is demyelination but axonal preservation (16,17). Clinical Features Pain, weakness, paresthesia, or burning in a single limb with a negative Spurling test that typically resolves within seconds to 24 hours and can be diagnosed on the field (13–15). Diagnostics Primarily a clinical diagnosis. Recurrent episodes or persistent symptoms may warrant further workup to include cervical spine plain films and MRI to evaluate for cervical stenosis (18). Management Neck injury red flag signs must first be ruled out (Table 3) (15). Tingling, pain, or paresthesia in >1 extremity, regardless of duration, at the time of injury warrants evaluation for spinal cord injury (18). After the first episode, athletes may return to play during the same game if symptoms resolve, which typically occurs within 15 minutes (18). After the second episode in a season, the athlete sits out for the remainder of the game but can return to playing in subsequent games if symptoms have resolved. Withhold the athlete from sport and order cervical spine imaging and electrodiagnostic studies if three episodes occur over an athlete’s lifetime or they have persistent symptoms (14,15,18). Conservative management can include myofascial stretches, shoulder flexibility, and stabilizing exercises. Cervical collars and specialized pads have not been shown to decrease the rate of injury (13,14). Table 3. - Neck injury red flag signs that may suggest spinal cord injury. Neck Injury Red Flags Bilateral symptoms Severe neck pain Decreased consciousness or unconscious athlete Paralysis Focal cervical spinous process tenderness Restricted or apprehensive cervical range of motion Adapted from Usman (15). The authors declare no conflict of interest and do not have any financial disclosures. The views expressed in this article are those of the author and do not necessarily reflect the official policy or position of the Defense Health Agency, Department of Defense, nor the U.S. Government.