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, quetiapine, 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 the prototypic atypical antipsychotic drug. Disappointing reports of risperidone-induced parkinsonism raise questions about the atypical nature of this drug. Olanzapine appears to be intermediate between risperidone and clozapine in inducing EPS. Drug-induced psychosis in Parkinson's disease and antipsychotic-induced movement disorders in psychotic patients are the most common indications for an atypical antipsychotic in patients with movement disorders. In drug-induced psychosis in Parkinson's disease, the antiparkinsonians are first reduced until psychosis resolves. Unfortunately, motor function is often compromised as a result. The addition of an atypical antipsychotic drug, without altering the regimen of antiparkinsonians, often controls psychosis without compromising motor function. Depending on the atypical antipsychotic used, the dosage required may be substantially lower than that for schizophrenic patients. No treatment strategy has been proven to be clearly superior in suppressing antipsychotic-induced movement disorders such as tardive dyskinesia. tardive akathisia and dystonia. Nonetheless, a review of the available data strongly suggests that clozapine has substantially less risk of inducing tardive dyskinesia as compared with conventional antipsychotic agents. Na case of tardive dyskinesia developing in patients who have taken clozapine as their only antipsychotic has vet been reported. Although there is evidence that clozapine may have an active therapeutic effect against pre-existing tardive dyskinesia, this remains inconclusive. Data on the use of clozapine for tremor in Parkinson's disease suggest significant benefit. Clozapine has also been reported to be useful in a variety of movement disorders including levodopa-induced dyskinesia, nocturnal akathisia and dystonia in Parkinson's disease, but the number of patients involved is small. No definitive conclusion on the role of atypical antipsychotic agents in other behavioural disorders such as depression, anxiety and sleep fragmentation in Parkinson's disease,. as well as in other movement disorders, can be made until well planned long term double-blind trials have been performed.