A 28-year-old male presents with loss of sensation over the lateral aspect of the forearm and weakness of elbow flexion following a motorcycle accident with a traction injury to the right upper limb. Clinical examination suggests upper trunk brachial plexus injury. Which investigation is most appropriate to confirm the diagnosis and assess the extent of nerve damage?

Explanation

## Investigation of Choice for Brachial Plexus Injury Assessment ### Why EMG/NCS is the Gold Standard **Key Point:** EMG and NCS are the most sensitive and specific investigations for confirming brachial plexus injury and determining the extent of nerve damage (axonal loss vs. demyelination). **High-Yield:** EMG/NCS can: - Detect denervation potentials (fibrillations, positive sharp waves) within 2–3 weeks of injury - Differentiate preganglionic (avulsion) from postganglionic lesions - Assess the severity of injury (Seddon: neurapraxia, axonotmesis, neurotmesis) - Guide prognosis and timing of surgical intervention - Detect subclinical involvement of other nerve roots ### Timing and Clinical Utility **Clinical Pearl:** EMG is most informative 3–4 weeks post-injury when denervation changes are well-established. Early NCS (within days) can show conduction block in neurapraxia. ### Role of MRI in Brachial Plexus Injury While MRI is useful for: - Visualizing preganglionic (root avulsion) injuries - Detecting associated soft-tissue injuries - Assessing spinal cord involvement It is **NOT the first-line confirmatory test** because it does not provide functional information about nerve conduction or denervation status, which is essential for prognosis and surgical decision-making. ### Comparison of Investigations | Investigation | Sensitivity for Nerve Injury | Functional Assessment | Preganglionic vs. Postganglionic | Timing Post-Injury | |---|---|---|---|---| | **EMG/NCS** | Very high (>95%) | Excellent | Yes (NCS absent in preganglionic) | 3–4 weeks optimal | | MRI | Moderate (detects avulsion) | None | Yes (visualizes root avulsion) | Anytime | | Plain radiograph | Low (fractures only) | None | No | Anytime | | CT myelography | Moderate (CSF leak) | None | Possibly (invasive) | Anytime | **Mnemonic:** **EMG-NCS FIRST** — Electromyography and Nerve Conduction Studies provide Functional, Injury-extent, Regeneration-status, and Surgical-timing information.