Abstract
Rabbit syndrome is a rare extrapyramidal side effect due to prolonged use of conventional antipsychotics characterised by rapid fine, rhythmic movements of the mouth along the vertical axis [1]. The differential diagnosis of Tardive Dyskinesia (TD) and rabbit syndrome is difficult, though reports suggest that tongue is spared in rabbit syndrome but not TD, anticholinergic medication improves rabbit syndrome whereas it may worsen TD, and physostigmine worsens the chewing movements of rabbit syndrome but may improve TD [2].
There are recent reports of marked improvement of TD following treatment with olanzapine [3]. We report a patient with rabbit syndrome with no improvement on anticholinergic treatment, who has shown dramatic reversal of the movement disorder with olanzapine.
A, a 31-year-old married female, was on haloperidol daily from the age of 17 after the onset of schizophrenia. She had a postpartum relapse of psychosis in 1996 which was managed by hospitalisation and later stabilised on haloperidol 5 mg/day. The rabbit syndrome was noted during hospitalisation. It was characterised by repeated chewing movements of the mouth which spared the tongue, and the movement disorder did not involve other facial, limbs or trunk muscles. Despite a reduction of haloperidol and the addition of 0.5 mg Benztropine daily, there was no improvement. There was no family history of any psychiatric illness or movement disorder. All investigations were within normal limits.
She had another relapse of psychosis with affective features in 1998 following caesarian section after the death of foetus-in-utero at 8 months. Her haloperidol was increased with addition of lithium and benztropine and there was no improvement of psychosis and movement disorder. Later haloperidol was changed to olanzapine and within 2 weeks her psychotic features and rabbit syndrome improved significantly. On follow up at 3 and 6 months, there was virtually no movement disorder and she was maintaining well.
The clinical description of this case is clearly of rabbit syndrome, though the non-response to anticholinergic drugs favours it as a variant of TD [4], which suggests the possibility of a spectrum of long-term movement disorders with rabbit syndrome, a less severe variant with the similar pathophysiology. The in vitro binding profile of olanzapine is similar to clozapine especially with respect to having more 5-hydroxytryptamine/2 than dopamine/2 activity [5]. Based on this observation and in view of the recent reports of improvement of dyskinetic symptom by novel antipsychotics it is plausible that olanzapine may have a therapeutic effect on all antipsychotics induced movement disorders.