Hemifacial spasm refers to unilateral painless, synchronous contractions of facial muscles due to repetitive involuntary electrical impulses from the 7th cranial (facial) nerve and/or its motor nucleus.
(See also Overview of Neuro-ophthalmologic and Cranial Nerve Disorders.)
Hemifacial spasm usually results from nerve compression by a pulsating blood vessel that causes ectopic impulse generation (ephaptic nerve impulses), similar to that in trigeminal neuralgia.
Unilateral, involuntary, painless contractions of facial muscles usually begin in the eyelid, then spread to the cheek and mouth. Contractions may be intermittent at first but may become almost continuous.
The pulsating blood vessel is often visible on MRI, but diagnosis of hemifacial spasm is ultimately clinical. Focal seizures, blepharospasm, and tics cause similar symptoms and should be considered.
The most effective treatment for hemifacial spasm is
Injection of botulinum toxin (botulinum toxin type A or botulinum toxin type B) into affected muscles
Treatments for trigeminal neuralgia (eg, antiseizure drugs, baclofen, amitriptyline, microvascular decompression) can also be used.
