In Bell's palsy, electrodiagnostic testing at 3 days shows 90% degeneration on electroneurography (ENoG). What does this finding indicate regarding prognosis?
- A Poor prognosis; >90% degeneration within first 2 weeks indicates Wallerian degeneration and risk of incomplete recovery ✓
- B Good prognosis; >90% degeneration is acceptable
- C Indeterminate; ENoG is only valid after 3 weeks
- D Excellent prognosis if the patient is started on steroids immediately
Correct answer: A. Poor prognosis; >90% degeneration within first 2 weeks indicates Wallerian degeneration and risk of incomplete recovery
Explanation
ENoG (electroneurography) compares compound action potential amplitude in the affected vs. normal side. When >90% degeneration occurs within the first 2 weeks (peak at 5-7 days), it indicates severe Wallerian degeneration and is associated with incomplete recovery in ~50% of patients. This threshold (>90% on ENoG) is also used as a guideline for surgical decompression consideration. EMG at 3 weeks showing no voluntary motor unit potentials further confirms poor prognosis.
Reference: Dhingra Diseases of Ear, Nose and Throat, 7th ed.
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Written and medically reviewed by the StethoPrep medical team.