Risperidone-induced rabbit syndrome: an unusual movement disorder

Rabbit syndrome is an antipsychotic-induced rhythmic motion of the mouth and lips, resembling the chewing motion of a rabbit. The motion consists of vertical movement; the tongue is not involved. The reported prevalence of rabbit syndrome ranges from 2.3% to 4.4% of patients treated with typical antipsychotic drugs. There have been isolated reports of rabbit syndrome in patients treated with atypical antipsychotics. Rabbit syndrome needs to be closely differentiated from tardive dyskinesia, the tongue-involving movement disorder. Treatment of rabbit syndrome is empirical, reflecting poor understanding of this syndrome. The striking aspect of this syndrome is its specificity. The etiology of rabbit syndrome focuses attention on the basal ganglia, which is also implicated in oral dyskinesia. Continuing neuro-physiological research of the basal ganglia probably holds the key to better understanding of this syndrome. The aim of this article is to create awareness of rabbit syndrome and its implications in clinical dentistry.