A new study finds that untreated Parkinson’s disease patients are no more likely to have impulse control disorders like gambling and impulse buying, than people without the disease. The researchers say their evidence is the strongest so far to suggest it is the drugs used to treat Parkinson’s that increase impulse control disorders in patients with the disease.
The researchers, from the Perelman School of Medicine at the University of Pennsylvania in the US, write about their findings in the 8 January issue of the journal Neurology.
Although it does not prove it, the study adds weight to the idea that dopamine-targeting drugs cause Parkinson’s patients’ to experience problems with impulse control.
Lead author Daniel Weintraub, associate professor of Psychiatry and Neurology at Perelman, says in a statement released on Monday:
“When looking at newly diagnosed Parkinson’s patients who had yet to be treated with drugs targeting the dopamine system, we saw no difference in impulsivity than what we found in healthy people without the disease.”
Impulse Control Disorders
Control of impulses or urges is one of the traits that separates humans from other species. The ability to think before acting gives us an opportunity to consider the consequences, and weigh up the pros and cons.
Impulse control disorders are more serious than occasionally not being able to resist that last piece of cake, or sometimes breaking a resolution not to buy any more shoes this year.
The inability to control impulses becomes a disorder when the consequences cause harm to self or others. Examples include but are not limited to, addictions to gambling, sex, spending, eating, and explosive attacks of rage.
People with impulse control disorders may or may not plan the impulsive actions, which usually satisfy short term wishes. But on the whole, most people with the condition feel they are losing control of their lives and find their disorders highly distressing.
Evidence Points to Dopamine-Targeting Drugs
Research suggests 1 in 5 Parkinson’s disease patients has impulse control disorder symptoms. But what this latest study appears to show, is that it is not the disease itself that increases the risk of gambling, shopping, or other impulsivity symptoms.
Previous studies have pointed to evidence of a link between drugs that target dopamine centers in the brain (dopamine agonist therapies) and impulse control disorders. Dopamine agonists work by increasing brain levels of dopamine, a neurotransmitter that helps control the brain’s reward and pleasure centers.
In March 2011, researchers at the Mayo Clinic reported a study that concluded dopamine agonists used in treating Parkinson’s disease result in impulse control disorders in as many as 22% of patients.
Parkinson’s Progression Markers Initiative (PPMI)
The study is the first to use and publish data from participants enrolled on the Parkinson’s Progression Markers Initiative (PPMI), a public-private funded project whose sponsors include The Michael J. Fox Foundation for Parkinson’s Research and commercial partners like Abbott, Biogen Idec, Pfizer Inc, F. Hoffman-La Roche Ltd., GE Healthcare, Genentech, and Avid Radiopharmaceuticals.
The study data came from 168 newly-diagnosed, untreated Parkinson’s disease patients and 143 healthy controls.
On enrolment, the PPMI participants also underwent a number of psychological assessments, including for depression and impulse control.
The impulse control measure was specifically developed and validated for use with Parkinson’s Disease. The researchers say this is the first study to use this measure and also to enrol Parkinson’s patients concurrently alongside healthy controls and to have both groups go through exactly the same baseline assessments.
The results showed that a diagnosis of Parkinson’s (in people not yet receiving treatment for the disease) was not associated with symptoms of any impulse control or related behavior.
The authors conclude, therefore, that Parkinson’s Disease itself does not seem to raise the risk for developing impulse control disorders.
However, they did find an increase of severity of depression linked to impulse control disorders in both groups, particularly in association with compulsive eating.
Weintraub says, now we have ruled out that it is not the disease itself that causes impulse control disorders:
“For those with Parkinson’s who screened positive for impulse control disorders at baseline, it will be interesting to follow the patients to see if treatment with dopamine agonists and other therapies will further increase risk over time.”
Written by Catharine Paddock PhD
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