A 60-year-old man with L4–L5 lumbar spinal stenosis presents with neurogenic claudication. Conservative management has failed after 6 months. On nerve conduction studies and EMG, the finding that would most strongly support surgical decompression is:

• A Evidence of active denervation (fibrillations) in L4–L5 innervated muscles (tibialis anterior, extensor hallucis longus) ✓
• B Reduced SNAP amplitude of the sural nerve bilaterally
• C Mildly prolonged F-wave latencies in peroneal nerve
• D Normal EMG findings with reduced walking tolerance only

Explanation

Active denervation (fibrillation potentials, positive sharp waves) on EMG in L4–L5 innervated muscles (tibialis anterior, extensor hallucis longus, L4/L5) signifies ongoing motor root damage and active neuronal loss — this finding, together with failed conservative management, strongly supports surgical decompression (laminectomy) before irreversible motor deficit occurs. SNAP abnormalities suggest peripheral polyneuropathy (common in diabetics). Mildly prolonged F-waves are non-specific. Normal EMG with reduced walking tolerance alone may still respond to conservative management. Active denervation on EMG is an objective neurophysiological correlate of significant radiculopathy justifying surgery.

Reference: Maheshwari Essential Orthopaedics, 6th ed.

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Written and medically reviewed by the StethoPrep medical team.