Approach Considerations
Early cases of hemifacial spasm may be difficult to distinguish from facial myokymia, tics, or myoclonus originating in the cortex or brainstem. Neurophysiologic testing can be invaluable.
Spread and variable synkinesis on blink reflex testing and high-frequency discharges on electromyography (EMG) with appropriate clinical findings are diagnostic. Stimulation of one branch of the facial nerve may spread and elicit a response in a muscle supplied by a different branch. Synkinesis is not present in essential blepharospasm, dystonia, or seizures. Needle EMG shows irregular, brief, high-frequency bursts (150–400 Hz) of motor unit potentials, which correlate with clinically observed facial movements.
Imaging and Other Studies
Magnetic resonance imaging is the imaging study of choice, especially if an underlying compressive lesion is suspected. Cerebral angiography offers little diagnostic value in hemifacial spasm. Ectatic blood vessels rarely are identified, and it is difficult to correlate vessels with the facial nerve. Perform angiography and/or magnetic resonance angiography prior to a vascular decompression surgical procedure. Angiography is often performed before decompressive surgery to clarify the vascular anatomy, because it may identify an aneurysm or vascular anomaly. [7]
Laboratory Studies
There are no known biological markers for hemifacial spasm.
