[A case of rabbit syndrome--its unique pharmacological feature].

A 61-year-old woman developed cerebellar ataxia as an initial symptom when she was 52 years old. Her neurological symptom was gradually followed by autonomic nervous system disturbance, pyramidal sign, and rigidity. She was diagnosed as suffering from multiple system atrophy (MSA), when she was 53 years old. Magnetic resonance imaging revealed atrophy of the cerebellum and brainstem. She was accompanied by rabbit syndrome (RS), when she was 61 years old. She had not been given any neuroleptics, which might produce RS, before she developed RS. Her regular involuntary movement was localized in lips, and its frequency was about 3 Hz. While sleeping, she did not have the involuntary movement. We had a chance to conduct pharmacological examination on RS. The administration of atropine or trihexyphenidyl did not change her symptom of RS, and the intravenous injection of levodopa deteriorated the movement. Haloperidol, sulpiride, or chlorpromazine was significantly effective on her involuntary movement of RS. These results indicated that our patient had the supersensitivity in her dopamine receptor. Such supersensitivity might result from the denervation in MSA, because she had not been administered any neuroleptics. RS is generally considered to be a kind of extrapyramidal sign, and we have not been aware of any report about RS, which levodopa deteriorated and neuroleptics improved. The mechanism of her symptom is discussed.