In Bell's palsy, the site of edema and nerve compression is classically at which narrowest segment of the facial canal, and the electrophysiological test that accurately predicts the degree of axonal degeneration within the first 2 weeks of onset is:
- A Tympanic segment; electromyography (EMG)
- B Mastoid segment; nerve excitability test (NET)
- C Labyrinthine segment; electroneuronography (ENoG) ✓
- D Geniculate ganglion; maximum stimulation test (MST)
Explanation
The labyrinthine segment of the facial nerve is the narrowest portion of the Fallopian canal (approximately 0.66 mm diameter) and is the site of maximum compression in Bell's palsy due to viral-mediated inflammation and edema. Electroneuronography (ENoG/ENOG), also called evoked electromyography, measures the compound muscle action potential (CMAP) amplitude compared to the normal side. A reduction >90% within 14 days predicts poor prognosis and may indicate need for surgical decompression. EMG detects fibrillation potentials after 2–3 weeks (indicating denervation) and motor unit potentials during recovery — it is useful after the 2-week acute window.
Reference: Dhingra Diseases of Ear, Nose and Throat, 7th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.