A Prospective Study of the Rabbit Syndrome

Rabbit Syndrome (RS) was described in 1972 as a peri-oral hyperkinetic disorder of 5–5.5 Hz frequency in association with long term neuroleptic drug therapy. It was differentiated from Tardive Dyskinesia (TD) with the help of two important fetures: persistence in Stage I NREM sleep and sparing of tongue. This paper presents data on 19 cases of RS identified during the last 13 years with descriptive criteria by Villeneuve (1972). The patients with RS were subjected to reduction of their neuroleptic dose if discontinuation was not feasible, introduction of anticholinergic agents following challenge with intravenous promethazine and spontaneous one night sleep EEG. They were followed up for a period of one to three years. The results indicate that RS dissappeared with intravenous promethazine which is a good differentiating strategy. The rabbit tremors did not persist in sleep and at least one-third of the patients had a lingual component. Follow up of these patients revealed that it can be effectively treated with anticholinergic drugs and development of RS did not predict future development of TD in the cohort. It therefore appears that some features of this disorder needs to be re-examined.