EMG of rectus capitis posterior minor muscle

Abstract

This chapter describes the anatomy and pathophysiology of hemifacial spasm (HFS). HPS begins in middle and later life and is more common in women than men, starts in the orbicularis oculi, and progresses to involve other facial muscles on the same side. The motor phenomena consist of spontaneous involuntary twitches, synkinetic movements, contracture, and slight weakness. It is found that although the hemifacial spasm following Bells palsy and other injuries to the facial nerve postparalytic HFS (PPHFS) is similar in character, there are clinical differences that separate the two entities and may imply different mechanisms for their pathophysiology. Spontaneous twitches, that is, those not initiated by voluntary movements, are much more obvious and frequent in HPS and much less obvious in PPHFS. The involuntary spasms vary over time with HFS, a phenomenon not seen with PPHFS. In HFS, during times of spontaneous twitches, synkinesis is prominent. The root entry zone is the proposed site in HFS, whereas more peripheral locations in the facial nerve are injured in PPHFS.