A 45-year-old patient develops House-Brackmann Grade IV facial palsy. Electroneuronography (ENoG) at 14 days shows 91% degeneration compared to the normal side. What does this finding most reliably predict, and what is the clinical implication?

• A Complete recovery is guaranteed regardless of management; no surgical intervention needed
• B ENoG at 14 days is too early; repeat testing at 6 weeks is needed before any decision
• C Steroid therapy must be started immediately as ENoG degeneration confirms acute inflammatory Bell's palsy
• D Greater than 90% degeneration within 14 days is a poor prognostic sign indicating axonotmesis/neurotmesis; surgical facial nerve decompression may be considered ✓

Explanation

ENoG (electroneuronography) comparing amplitude of the compound motor action potential (CMAP) between the paralyzed and normal sides measures the percentage of degenerated fibers. Greater than 90% degeneration within 14 days of onset (the time window before wallerian degeneration is complete) is an established indicator of severe nerve injury with poor prognosis for complete spontaneous recovery. This threshold is used as an indication for surgical facial nerve decompression (transmastoid or middle fossa approach) in Bell's palsy or temporal bone trauma, though the evidence for surgery is debated. Steroid therapy is indicated early (within 72 hours of onset) not based on ENoG at 14 days.

Reference: Dhingra Diseases of Ear, Nose and Throat, 7th ed.

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Written and medically reviewed by the StethoPrep medical team.