• Intermittent clonic or tonic contraction of muscles supplied by facial nerve. Muscles are relaxed in between contractions.
  Human Phenotype Ontology (HPO)
  The Human Phenotype Ontology Project, 2025
• Recurrent clonic contraction of facial muscles, restricted to one side. It may occur as a manifestation of compressive lesions involving the seventh cranial nerve (FACIAL NERVE DISEASES), during recovery from BELL PALSY, or in association with other disorders. (From Adams et al., Principles of Neurology, 6th ed, p1378)
  NLM Medical Subject Headings
  U.S. National Library of Medicine, 2025
• 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.
  Merck Manuals
  Merck & Co., Inc., 2025
• First described by Gowers in 1884, hemifacial spasm represents a segmental myoclonus of muscles innervated by the facial nerve. The disorder presents in the fifth or sixth decade of life, almost always unilaterally, although bilateral involvement may occur rarely in severe cases.
  Medscape
  WebMD, 2025
• Hemifacial spasm is a nervous system disorder in which the muscles on one side of your face twitch involuntarily. Hemifacial spasm is most often caused by a blood vessel touching a facial nerve, but it may be caused by a facial nerve injury or a tumor, or it may not have a cause.
  Mayo Clinic
  Mayo Foundation for Medical Education and Research, 2025