Hemifacial spasms are involuntary twitches or contractions
on one side of the face. These twitches are paroxysmal spurts of involuntary
tonic or clonic activity in the muscles that innervated by the facial nerve.
When spasms occur, the facial muscles, which are operated by
the facial nerve (seventh cranial nerve), have sudden spurts of involuntary
tonic and clonic activity. The facial nerve is what moves the lips, mouth,
raises and lowers the eyebrows, and also closes the eyelids. These facial
contractions can happen sporadically or can be constant but occur often and
involuntarily.
Hemifacial spasms can occur due to damage to the facial
nerve, compression on the nerve from a blood vessel, and also Bell’s palsy,
also known as idiopathic facial paralysis. The most prevalent cause is pressure
from a blood vessel which causes the nerve to misfire, triggering the
contraction.