Recovery of Impaired Endogenous Pain Modulation by Dopaminergic Medication in Parkinson's Disease

Abstract

Background: Of patients with Parkinson's disease (PD), 30% to 85% report pain. However, mechanisms underlying this pain remain unclear. In line with known neuroanatomical impairments, we hypothesized that pain in PD is caused by alterations in emotional-motivational as opposed to sensory-discriminative pain processing and that dopamine recovers the capacity for endogenous emotional-motivational pain modulation in patients with PD. Methods: A total of 20 patients with PD played a random reward paradigm with painful heat stimuli in addition to assessments of pain sensitivity once with and once without levodopa. Results: Levodopa increased endogenous pain inhibition in terms of perceived pain intensity and un/pleasantness compared with a medication off state. Higher clinical pain was associated with higher increases in pain inhibition. Levodopa did not affect heat pain threshold, tolerance, or temporal summation. Conclusion: Patients with PD seem to be predominately impaired in emotional-motivational as opposed to sensory-discriminative pain processing. A differential understanding of pain in PD is urgently needed because effective treatment strategies are lacking.