Intertemporal choice in Parkinson's disease and restless legs syndrome

Background: Impulse control disorders in Parkinson's disease are a potential consequence of dopaminergic therapy. Impulse control problems might be revealed by intertemporal choice tasks which entail to forgo an immediately available reward in favor of a larger but later reward. The steepness of the discounting curve can be quantified by the parameter k. Methods: Participants (37 Parkinson patients [13 de novo, 24 medicated], 24 patients with restless legs syndrome, and 22 controls) were offered 54 choices between immediate smaller rewards and delayed larger and the k value was estimated from the participants' responses. Participants had the chance of winning one of their decisions. None of the participants had impulse control disorders. Results: Unmedicated Parkinson patients had a higher discounting rate than controls and medicated patients with restless legs syndrome. The k values of medicated Parkinson patients and patients with restless legs syndrome did not differ from those of controls. No correlation was found between the k value and the dopamine agonist dose. Conclusion: Impulsive decision making in patients with Parkinson's disease may occur as part of the disease rather than as a consequence of dopamine agonist therapy.