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Dyskinesia refers to involuntary movements, similar to a tic or chorea. Dyskinesia is a symptom of several medical disorders and is distinguished by the underlying cause. When a dyskinesia presents after treatment with an antipsychotic drug such as haloperidol, it is a tardive dyskinesia and is commonly found in face as tongue "rolling". A dyskinesia found in a patient with Parkinson's disease is more commonly a jerky, dance-like movement of the arms or head and usually presents after several years of treatment with medication containing l-dopa.

Two other conditions, primary ciliary dyskinesia and biliary dyskinesia, refer to involuntary movements of internal organs.

In the context of Parkinson's disease, dyskinesias are often the result of chronic levodopa (L-dopa) therapy. These motor fluctuations occur in more than half of PD patients after 5 to 10 years of levodopa therapy, with the percentage of affected patients increasing over time.^[1] Dyskinesias most commonly occur at the time of peak L-dopa plasma concentrations and are thus referred to as peak-dose dyskinesias. As patients advance, they may evidence diphasic dyskinesias, which occur when the drug concentration rises or falls. Attempts to moderate dyskinesias by the use of other treatments such as bromocriptine appear to have been unsuccessful. ^[2] In order to avoid dyskinesia, patients with the young-onset form of the disease (YOPD) are often hesitant to commence l-dopa therapy until absolutely necessary for fear of suffering severe dyskinesia.

Patients with severe dyskinesia resulting from high doses of parkinsonian medication may benefit from deep brain stimulation(DBS), which benefits the patient in two ways. Firstly, DBS allows a reduction in l-dopa dosage of 50-60% (thus tackling the underlying cause). Secondly, DBS treatment itself (in the subthalamic nucleus or globus pallidus can reduce dyskinesias. ^[3]

The use of MDMA has been shown to enhance the effects of L-Dopa while reducing the associated dyskinesia in primates with simulated Parkinson's disease.^[4]