Risperidone-induced rabbit syndrome: an unusual movement disorder caused by an atypical antipsychotic.

Rabbit syndrome is a rare side effect of chronic neuroleptic administration characterized by rapid, fine, rhythmic movements of the mouth along a vertical axis. It gains its name from an unusual resemblance to the chewing and puckering motions of the rabbit. It is generally thought to be an extra-pyramidal side effect, in part due to its rapid response to anti-cholinergic medication. This is the first case report of risperidone, an atypical antipsychotic, inducing the syndrome. The theoretical implications for the classification of the syndrome along the spectrum of neuroleptic-induced movement disorders are discussed.