The rabbit syndrome: state of the art.

INTRODUCTION: The rabbit syndrome (RS) is a rare movement disorder generally associated with prolonged use of antipsychotics and characterized by inwilling, rhythmic, fast and fine movements of oral and masticatory muscles along the vertical axis of the mouth. PREVALENCE: The prevalence of RS ranges between 1.5% and 4.4%; middle and elderly ages, the female gender, as well as past brain injuries are considered risk factors for its development. PATHOPHYSIOLOGY: Although a dysbalance of the cholinergic and dopaminergic neurotransmission in the basal ganglia seems to be involved in the pathophysiology of RS, its precise mechanisms need to be clarified as yet. RELATIONSHIPS WITH ANTIPSYCHOTICS: Fifty cases of RS have been published up-to-now: 34 and 10 occurred during treatments with typical and atypical antipsychotics, respectively, while 6 seemed unrelated to these drugs. DIFFERENTIAL DIAGNOSIS: The differential diagnosis between RS and tardive dyskinesias involving the mouth may be based mainly on the evidence that in these last conditions the movements of the mouth are less regular and slower and involve the tongue. Treatment strategy: The available data suggest that RS responds favourably to anticholinergic drugs and to the change of the antipsychotic.