People taking dopamine agonists to treat Parkinson's disease are at risk for impulse-control disorders such as compulsive gambling, buying and sexual behaviour, University of Pennsylvania researchers report.
In fact, people taking these particular medications are three times more likely to engage in these behaviours compared with Parkinson's patients not taking these drugs.
The connection is not entirely new.
"Impulse-control disorders are relatively common in Parkinson's disease," said lead researcher Dr Daniel Weintraub, an assistant professor of psychiatry. "In almost 14 percent of treated Parkinson's disease, patients had at least one of the four impulse-control disorders."
Of the 14 percent, about a third had more than one impulse-control disorder, Weintraub said. Most research on compulsive behaviours in Parkinson's disease is focused on gambling, Weintraub said. "We found that the other three impulse-control disorders occurred as commonly as compulsive gambling," he noted.
Risk may increase threefold
In the study, Weintraub's team looked at these compulsive behaviours in 3 090 patients taking dopamine agonists for Parkinson's disease and Parkinson's patients not taking these drugs.
The researchers followed the patients for six months. Weintraub's team found a twofold to threefold increased risk for these four compulsive behaviours among those taking dopamine agonists.
In addition, patients taking levodopa were also prone to impulse-control disorders, Weintraub said. Higher doses of levodopa or dopamine agonists increase the risk of developing an impulse-control disorder, he said.
"Doctors and patients should be aware that development of one or more impulse-control disorders is a potential risk factor for Parkinson's patients that are treated with a dopamine agonist," Weintraub said.
In addition, younger patients and those taking levodopa and patients with a family history of similar behaviours may be at higher risk of developing impulse-control disorders, Weintraub said.
Since people taking higher doses of these drugs are more susceptible to impulse-control disorders, doctors should prescribe only the highest dose needed to control Parkinson's symptoms, Weintraub advised.
Challenges for treating Parkinson's
Michael W. Jakowec, an assistant professor of neurology at the University of Southern California, said that "these compulsive disorders reflect clinical challenges faced in the treatment of Parkinson's disease, especially in the context of dopamine-replacement strategies."
While dopamine is necessary for control of the aspects of motor control, it also plays an important role in other regions of the brain, particularly those involved in reward systems, Jakowec explained.
"There are a number of behaviours we are subject to that are a balance between reward-reinforcement-aversion," Jakowec said. "A dysfunction in the reward system can lead to an imbalance such that compulsive behaviours emerge."
It is very similar to drug addiction, where drug dependence is reflected in dopamine dysfunction, Jakowec said.
"So, it is not surprising that there are behavior similarities between these disorders," Jakowec said. "What we learn in Parkinson's disease with respect to non-motor features of the disorders will also impact similar behaviors in other disorders including drug addiction and compulsive disorders." – (Steven Reinberg/HealthDay News)
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