2025 Workshop Handout Bundle-W99C Facial NCS and Blink Reflex Studies

W99C Facial NCS and Blink Reflex Studies - Katirji

Pdf Summary

This document, presented by Dr. Bashar Katirji at the AANEM Workshop 2024, provides a comprehensive overview of facial nerve and blink reflex studies, particularly their anatomy, diagnostic techniques, and clinical applications.<br /><br />Anatomically, the facial nerve originates in the caudal pons, follows a long intraosseous path, exits through the stylomastoid foramen, and branches variably within the parotid gland to innervate facial muscles. The trigeminal nerve, with sensory and motor divisions, also plays a key role in facial sensation and reflex arcs.<br /><br />Electrical stimulation of the facial nerve trunk near the ear elicits motor compound muscle action potentials (CMAP) in facial muscles, commonly recorded from the nasalis or orbicularis oculi muscles. Normal CMAP amplitude (~1.2 mV) and latency parameters help determine nerve health, while branch-specific stimulation allows localized assessment.<br /><br />The blink reflex test evaluates interaction between the trigeminal (afferent) and facial (efferent) nerves via supraorbital nerve stimulation. It elicits two responses: R1 (ipsilateral, oligosynaptic) and R2 (bilateral, polysynaptic) with established normal latency benchmarks used to detect abnormalities.<br /><br />Clinically, facial nerve studies aid in diagnosing conditions like Bell’s palsy, where M response amplitude reduction indicates axonal loss and prognosis. Blink reflex abnormalities help identify facial or trigeminal nerve lesions, including tumors, polyneuropathies (e.g., GBS, CIDP), and hemifacial spasm, distinguishing demyelinating vs. axonal pathology. Synkinesis after nerve injury is detected by simultaneous recordings from multiple facial muscles revealing aberrant reinnervation patterns.<br /><br />Electromyography (EMG) of facial muscles, such as masseter and orbicularis oris, reveals spontaneous activity and motor unit potential changes important for lesion localization and nerve regeneration evaluation. The document stresses careful technique to avoid cross-muscle interference and recognizes contralateral reinnervation challenges.<br /><br />Overall, electrical stimulation studies of facial and trigeminal nerves, along with blink reflex testing and EMG, provide crucial diagnostic and prognostic information for various facial nerve disorders, guiding clinical management and understanding of pathophysiology.

Keywords

Facial nerve anatomy

Blink reflex test

Electrical stimulation

Compound muscle action potentials

Trigeminal nerve

Bell's palsy diagnosis

Electromyography (EMG)

Synkinesis detection

Polyneuropathies (GBS, CIDP)

Nerve regeneration evaluation