The role of atypical antipsychotics in the treatment of movement disorders

An atypical antipsychotic drug is loosely defined by its ability to produce an antipsychotic effect without inducing extrapyramidal symptoms (EPS). To date, 4 atypical antipsychotics have been released in the US: clozapine, q uetiapine, olanzapine and risperidone, which are listed in decreasing order of 'atypicality' based on clinical and preclinical studies. While we await the outcome of trials with quetiapine on parkinsonian patients (considered the most stringent test of the atypicality of a drug), clozapine remains t he prototypic atypical antipsychotic drug. Disappointing reports of risperi done-induced parkinsonism raise questions about the atypical nature of this drug. Olanzapine appears to be intermediate between risperidone and clozap ine in inducing EPS. Drug-induced psychosis in Parkinson's disease and antipsychotic-induced mov ement disorders in psychotic patients are the most common indications for a n atypical antipsychotic in patients with movement disorders. In drug-induc ed psychosis in Parkinson's disease, the antiparkinsonians are first reduce d until psychosis resolves. Unfortunately, motor function is often compromi sed as a result. The addition of an atypical antipsychotic drug, without al tering the regimen of antiparkinsonians, often controls psychosis without c ompromising motor function. Depending on the atypical antipsychotic used, t he dosage required may be substantially lower than that for schizophrenic p atients. No treatment strategy has been proven to be clearly superior in suppressing antipsychotic-induced movement disorders such as tardive dyskinesia. tardi ve akathisia and dystonia. Nonetheless, a review of the available data stro ngly suggests that clozapine has substantially less risk of inducing tardiv e dyskinesia as compared with conventional antipsychotic agents. Na case of tardive dyskinesia developing in patients who have taken clozapine as thei r only antipsychotic has vet been reported. Although there is evidence that clozapine may have an active therapeutic effect against pre-existing tardi ve dyskinesia, this remains inconclusive. Data on the use of clozapine for tremor in Parkinson's disease suggest sign ificant benefit. Clozapine has also been reported to be useful in a variety of movement disorders including levodopa-induced dyskinesia, nocturnal aka thisia and dystonia in Parkinson's disease, but the number of patients invo lved is small. No definitive conclusion on the role of atypical antipsychot ic agents in other behavioural disorders such as depression, anxiety and sl eep fragmentation in Parkinson's disease,. as well as in other movement dis orders, can be made until well planned long term double-blind trials have b een performed.