Blink reflex excitability cycle in hemifacial spasm.

Area of Science:

• Neuroscience
• Clinical Neurology
• Electrophysiology

Background:

• Hemifacial spasm (HFS) is a neuromuscular disorder characterized by involuntary contractions of facial muscles.
• The blink reflex is a well-established neurophysiological test to evaluate the integrity of the trigeminal and facial nerve pathways.
• Understanding the underlying pathophysiology of HFS can lead to improved diagnostic and therapeutic strategies.

Purpose of the Study:

• To investigate alterations in the electrically elicited blink reflex in patients with hemifacial spasm.
• To compare blink reflex responses between the affected and unaffected sides of the face, as well as with healthy controls.
• To explore the relationship between disease duration and blink reflex abnormalities in HFS.

Main Methods:

• Electrically elicited blink reflex responses were recorded using single and paired stimuli applied to both sides of the face.
• Analysis focused on the amplitude of early and late responses (R1 and R2) and the recovery curve of the R2 response.
• Patients with HFS were compared to a control group of healthy individuals.

Main Results:

• Single stimuli elicited larger blink reflex responses on the affected side in HFS patients compared to the unaffected side and controls.
• Paired stimuli revealed a significantly reduced inhibitory effect on the late response (R2) at short interstimulus intervals in HFS patients.
• An enhanced R2 recovery curve was observed on both the affected and clinically normal contralateral sides in HFS patients, more pronounced with longer disease duration.

Conclusions:

• Patients with hemifacial spasm demonstrate enhanced excitability within the blink reflex pathway.
• This heightened excitability involves both facial motoneurons and brainstem interneurons mediating the blink reflex.
• The observed abnormalities in the blink reflex recovery curve may serve as a biomarker for HFS pathophysiology.