SAN DIEGO – Obsessive or impulsive reward-based behavior was reported by nearly 6 in 10 patients with Parkinson's disease answering an anonymous survey, adding to the suspicion that dopaminergic medications may influence impulse control.
Patients who had suffered from Parkinson's disease for more than 5 years, as well as those taking certain combinations of medications, were most likely to report such behaviors as obsessive or recurrent thoughts, the need to repeatedly check or organize, or impulsive eating, shopping, or gambling.
Dr. Jennifer S. Hui and her associates at the movement disorders center of the University of Southern California, Los Angeles, distributed anonymous questionnaires to 161 patients with Parkinson's disease. Among the 97 patients who returned surveys, 57 acknowledged engaging in at least one reward-based behavior, 34 respondents reported two such behaviors, and 20 acknowledged three or more.
The most commonly reported behaviors were obsessive or recurrent thoughts (25 patients); the urge to repeatedly check or organize (21 patients); the urge to go shopping (15); feeling the need to eat or starve (13); the urge to gamble (12); and an increased interest in sex (10).
In smaller numbers, patients endorsed a wide range of behaviors–including an increased interest in pornography, a change in usual sexual practices, the desire to increase the dose of medications for enhanced mood, and the need to “live on the edge”–and even reported compulsive bridge playing.
Nearly half of patients felt these behaviors represented a “distinct change in their personalities,” Dr. Hui reported in a poster presented at the annual meeting of the American Neurological Association.
Patients reporting reward-based behaviors were more likely than were others to be taking combinations of medications, especially Sinemet (carbidopa/levodopa) and Mirapex (pramipexole dihydrochloride). In the survey, 16 of 19 patients taking that combination of drugs acknowledged obsessive or impulsive behavior. Nine of 14 patients taking Sinemet (carbidopa/levodopa) and Requip (ropinirole) also reported such behaviors.
Some have theorized that dopamine agonists may contribute to reward-based behaviors because of their effect on the dopaminergic mesolimbic reward circuit. Other factors, such as personality, genetic susceptibility, and brain changes associated with the disease itself, may be involved as well, Dr. Hui said in an interview.
Although the science is far from clear, class action suits were filed in the United States and Canada last year alleging that Mirapex, manufactured by Boehringer Ingelheim, was responsible for their gambling addiction.
Dr. Hui said several prospective studies are underway to further clarify the issue, including one that will follow patients from the time they begin taking dopamine agonists, to examine the effect of personality, medication, and comorbid depression on the expression of reward-based behaviors.
“We have just started to enroll, but already two patients have described a distinct change in their behavior (hypersexuality and rearranging/shopping) within weeks of starting the agonist,” she noted.
On the other hand, 6 of 15 patients in the study presented at the meeting were not taking any of the three listed dopamine agonist medications, and yet they said they, too, suffered from impulse-control behaviors.
The likely explanation, then, is that combinations of factors probably contribute to the behaviors, although drugs theoretically could certainly play a key role.
“The dopaminergic mesolimbic mesocortical system is the core circuit underlying subjective pleasure produced by food, sex, and pathological addictions. Recent positron emission tomography (PET) studies have indicated the dopaminergic reward circuitry is deficient in Parkinson's disease,” Dr. Hui and her coinvestigators concluded.
“The effect of exogenous dopamine on this altered reward system may explain behavioral abnormalities in Parkinson's disease patients.”