Pain and dyskinesia in Parkinson's disease may share common pathophysiological mechanisms - An fMRI study

Background: Parkinson's disease (PD) patients develop levodopa induced dyskinesia with disease progression from sensitization of central pathways. Pain pathways are also impacted with suggestions dyskinetic patients may process pain differently. Objective: Establish if centrally sensitized nociceptive pathways are altered and dopaminergically driven in dyskinetic patients. Methods: Clinical characteristics, affect, pain thresholds and sensitivity to pressure stimulation in the ON and OFF medication states as well as distribution of pain related activation of cortical regions on BOLD fMRI were assessed and compared between groups of patients suffering from dyskinesia and not. Results: Dyskinetic PD participants experienced increased pressure pain sensitivity. This was associated with increased pressure induced pain > innocuous BOLD activity in areas associated with encoding pain intensity, pain spatial orientation, descending pain mediation, sensorimotor integration, and motor control. Levodopa reduced pressure pain ratings and improved negative affect, though did not impact BOLD activity differently between the groups. Conclusion: Dyskinetic PD patients experience increased pain sensitivity and centrally sensitized nociceptive pathways resembling levodopa induced sensitization though this is not directly influenced by dopamine.