Masticatory spasm in facial hemiatrophy.

Spontaneous spasms began in the left masseter muscle six years following the onset of facial hemiatrophy in a young woman. A dental procedure had preceded the original facial wasting by four weeks. The electromyographic findings were similar to those described in hemifacial spasm and consisted of brief bursts of one to four morphologically different potentials, each firing at rates of up to 200 Hz. The findings demonstrate that spontaneous activity due to nerve injury can arise in muscles innervated by the trigeminal nerve.