What is the initial diagnostic approach to brachial plexopathy?

Diagnostic Approach to Brachial Plexopathy

MRI of the brachial plexus is the initial diagnostic imaging modality of choice for evaluating brachial plexopathy due to its superior soft-tissue contrast and spatial resolution, providing detailed definition of intraneural anatomy and localizing pathologic lesions when clinical and electrodiagnostic findings are nonspecific. 1

Initial Diagnostic Algorithm

Step 1: Clinical Evaluation

• Assess for pain, weakness, and sensory loss across multiple peripheral nerve distributions in the shoulder and arm, which distinguishes plexopathy from radiculopathy 2
• Evaluate for flaccid loss of tendon reflexes in regions innervated by the affected plexus 3
• Note that pain distribution crossing multiple dermatomes helps differentiate plexopathy from radiculopathy 3

Step 2: Electrodiagnostic Studies

• Perform electrodiagnostic testing no sooner than 4 weeks after injury (if traumatic) unless clinically indicated earlier 4
• Focus on sensory nerve amplitudes, which are most important for distinguishing between pre-ganglionic and post-ganglionic injuries 4
• Use EMG to determine the level of plexus involvement and identify potential donor nerves for transfers if surgical intervention is being considered 4

Step 3: Imaging

• MRI of the brachial plexus is the primary imaging modality with:

  • Sensitivity of 81%, specificity of 91%, and accuracy of 88% compared to surgical findings and clinical follow-up 1
  • Ability to provide additional information beyond clinical evaluation and electrodiagnostic studies in 45% of patients 1
  • Capability to reliably differentiate compressive from noncompressive plexopathy 1

• MRI protocol should include:

  • Orthogonal views through the oblique planes of the plexus 1
  • T1-weighted, T2-weighted, fat-saturated T2-weighted or STIR sequences 1
  • Fat-saturated T1-weighted post-contrast sequences when appropriate 1

• MRI with and without IV contrast is recommended as it can:

  • Detect and characterize several etiologies in the differential diagnosis 1
  • Provide additional information over non-contrast MRI 1

Step 4: Complementary Imaging (When Indicated)

• MRI of the cervical spine may be complementary when:

  • Clinical uncertainty exists whether symptoms represent plexopathy or radiculopathy 1
  • Often performed prior to brachial plexus MRI due to higher prevalence of radiculopathy-related degenerative spine disease 1

• CT with IV contrast can be considered when:

  • MRI is contraindicated 1
  • Offers the next highest level of anatomic visualization after MRI 1
  • Useful for detecting and characterizing soft-tissue masses and tumors 1

Differential Diagnosis Considerations

Neoplastic Causes

• Primary tumors: benign peripheral nerve sheath tumors (schwannomas and neurofibromas) 2
• Malignant peripheral nerve sheath tumors: rare, more frequent in neurofibromatosis type 1 2
• Secondary involvement: direct invasion or metastasis from adjacent tumors (lung cancer, breast cancer) 2

Inflammatory/Immune-Mediated Causes

• Parsonage-Turner syndrome (neuralgic amyotrophy or brachial plexitis): characterized by acute onset of pain followed by weakness 2, 5
• Chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) 2
• Other inflammatory neuropathies (multifocal motor neuropathy, Lewis-Sumner syndrome) 1

Traumatic Causes

• May result in preganglionic (root avulsion) or postganglionic injuries 2, 6
• Compression injuries may present with delayed onset of symptoms 6

Other Causes

• Radiation-induced plexopathy 2
• Infectious causes 1, 2
• Hereditary neuropathies (e.g., Charcot-Marie-Tooth syndrome) 1
• Idiopathic causes 7

Common Pitfalls and Caveats

• Misdiagnosis as radiculopathy: Plexopathy affects multiple peripheral nerve distributions whereas radiculopathy follows a single dermatome distribution 2, 3
• Delayed diagnosis of compression injuries: Some compression-related plexopathies may not be evident for 48 hours after initial injury 6
• Incomplete imaging: Standard neck or cervical spine MRI does not adequately evaluate the brachial plexus; dedicated brachial plexus MRI protocol is required 1
• Premature electrodiagnostic testing: EMG performed too early (less than 4 weeks after injury) may yield false negative results 4
• Failure to distinguish pre-ganglionic from post-ganglionic lesions: This distinction is crucial as treatment approaches differ significantly 2, 4
• Overlooking brachial neuritis without typical presentation: Up to 47% of patients with brachial neuritis do not have pain before onset, and only 28% have a definable antecedent illness 5