2026 Workshop Handout Bundle-W99C - Facial NCS and Blink Reflexes

W99C - Facial NCS and Blink Reflexes - Katirji

Pdf Summary

This workshop reviews facial nerve conduction studies, blink reflexes, and facial muscle electromyography. The facial nerve supplies the muscles of facial expression and also carries taste, sensory, and parasympathetic fibers. The blink reflex assesses both trigeminal sensory input and facial motor output, along with brainstem connections.<br /><br />Facial nerve stimulation below the ear produces a compound muscle action potential (CMAP), commonly recorded from the nasalis. A side-to-side amplitude difference of 50% or more is abnormal; the upper normal latency is 4.1 ms, with a maximum side-to-side latency difference of 0.6 ms. Supraorbital nerve stimulation produces an ipsilateral, short-latency R1 and bilateral, longer-latency R2 responses. Key upper normal limits are 13 ms for R1, 40 ms for ipsilateral R2, and 41 ms for contralateral R2.<br /><br />In Bell’s palsy, facial nerve conduction and blink reflex findings help assess injury and prognosis. Reduced CMAP amplitude indicates axonal loss, while a preserved response after the first week may suggest conduction block and a better prognosis. R1 is typically delayed or absent on the affected side; abnormal R2 responses can indicate facial motor pathway involvement. Gradual onset, bilateral palsy, other cranial nerve findings, severe pain, or lack of improvement are warning signs that warrant consideration of alternative diagnoses.<br /><br />Blink reflex testing can also help identify trigeminal nerve or brainstem lesions, cerebellopontine angle tumors, and abnormalities associated with polyneuropathies. Recording from additional facial muscles may reveal synkinesis due to aberrant nerve regeneration or hemifacial spasm; variable responses may support ephaptic transmission. Needle EMG can identify denervation and reinnervation, though facial muscle signals require careful interpretation because normal motor units are small and brief.

Keywords

facial nerve conduction studies

blink reflex

facial muscle electromyography

Bell's palsy

compound muscle action potential

trigeminal nerve

brainstem lesions

R1 response

R2 response

denervation reinnervation