What is the best way to distinguish radicular entrapment and peripheral nerve entrapment?

Distinguishing Radicular Entrapment from Peripheral Nerve Entrapment

MRI is the most effective diagnostic tool for distinguishing between radicular entrapment and peripheral nerve entrapment, with brachial or lumbosacral plexus MRI providing superior diagnostic accuracy compared to spine MRI alone. 1

Clinical Presentation Differences

Radicular Entrapment (Radiculopathy)

• Pain radiates in a dermatomal distribution
• Sensory loss follows specific dermatomes
• Motor weakness corresponds to myotomes
• May present with increased tendon reflexes and/or muscle tone
• Often associated with spine pathology (disc herniation, foraminal stenosis)

Peripheral Nerve Entrapment

• Pain, sensory loss, and weakness follow peripheral nerve distribution (crossing multiple dermatomes)
• Symptoms typically worsen with specific movements or positions
• Often presents with negative spine imaging despite neurological symptoms
• Usually no changes in tendon reflexes

Diagnostic Algorithm

1. Electrodiagnostic Studies (First-line)

   • Nerve conduction studies (NCS) and needle electromyography (EMG) are essential 1, 2
   • EMG has up to 90% sensitivity for lumbosacral radiculopathy 2
   • EMG of paraspinal muscles increases sensitivity to nearly 100% 2
   • NCS can identify peripheral nerve entrapment by showing focal slowing across the entrapment site 3
   • Radiculopathy may show normal nerve conduction with abnormal EMG findings 3

2. Advanced Imaging

   • For suspected radiculopathy: MRI of the cervical or lumbar spine 1
   • For suspected plexopathy/peripheral entrapment: Dedicated MRI of the brachial or lumbosacral plexus 1
   • Brachial plexus MRI has 81% sensitivity, 91% specificity, and 88% accuracy for plexopathy 1
   • Plexus MRI provides additional information beyond clinical and electrodiagnostic studies in 45% of patients 1

3. Complementary Studies

   • When clinical findings are equivocal, both spine and plexus MRI may be needed 1
   • Ultrasound can be a useful adjunctive tool for peripheral nerve assessment 1

Key Distinguishing Features

Anatomical Considerations

• Radicular entrapment occurs at or near the neural foramina
• Peripheral nerve entrapment occurs at specific anatomical sites:
  • Carpal tunnel (median nerve)
  • Cubital tunnel (ulnar nerve)
  • Radial tunnel (posterior interosseous nerve)
  • Piriformis syndrome (sciatic nerve) 1

Progression Patterns

• Peripheral nerve entrapment typically progresses through three stages 4:
  • Stage I: Rest pain and intermittent paresthesias (worse at night)
  • Stage II: Persistent paresthesias, numbness, and occasional muscle weakness
  • Stage III: Constant pain, muscle atrophy, and permanent sensory loss

Clinical Pearls and Pitfalls

Common Pitfalls

• Relying solely on MRI findings without correlating with clinical symptoms and electrodiagnostic studies 1
• Failing to recognize that degenerative findings on MRI are common in asymptomatic patients over 30 years 1
• Missing peripheral nerve entrapment when focusing only on spine pathology

Important Considerations

• MRI of the cervical spine is inferior to brachial plexus MRI for evaluating brachial plexopathy 1
• Lumbosacral plexus MRI can detect lateral disc herniations that compress nerve roots outside the neural foramina, which may be missed on standard lumbar spine MRI 1
• EMG without paraspinal muscle examination may miss radicular pathology 2

Conclusion for Clinical Practice

When distinguishing between radicular and peripheral nerve entrapment, the combination of detailed electrodiagnostic studies and targeted MRI provides the most accurate diagnosis. EMG with paraspinal muscle mapping is particularly valuable for identifying radiculopathy, while nerve conduction studies showing focal slowing are characteristic of peripheral nerve entrapment. In cases where clinical presentation is unclear, both spine and plexus MRI may be necessary to establish the correct diagnosis and guide appropriate treatment.