title: Asymmetric pain processing in Parkinson's disease.
abstract: OBJECTIVE
  Reduced endogenous pain inhibition, as part of the degenerative process, is presumed to be the mechanism underlying the common presence of pain in patients with Parkinson's disease (PD). The present study aimed to assess an endogenous pain inhibitory system in PD using the conditioned pain modulation paradigm.
  
  
  METHODS
  Twenty-six predominantly unilateral PD patients and 19 controls underwent psychophysical pain assessment before and after patients' morning dopaminergic medication.
  
  
  RESULTS
  An unexpected increase in several parameters of pain perception for PD patients was found after dopaminergic medication (e.g. for 49°C noxious heat stimulation an increase from 70.6 ± 4.0 to 77.6 ± 4.0 on the numerical pain scale, P < 0.001). This increase was seen in patients with predominantly left-sided PD, regardless of the stimulated side (for 49°C noxious heat stimulation, predominantly left-sided PD patients, pain perception increased from 73.5 ± 6.8 to 85.0 ± 6.8, P < 0.001, whereas predominantly right-sided PD patients did not show a significant increase, 68.3 ± 6.8 to 70.4 ± 6.5, P = 0.777). Baseline efficiency of conditioned pain modulation inversely correlated with age at disease onset (r = -0.522; P = 0.009) and disease severity (Unified PD Rating Scale, r = 0.447; P = 0.032) but did not differ between patients and controls.
  
  
  CONCLUSIONS
  Increased sensory response causing hyperalgesia occurs after dopaminergic medication in patients with predominantly left-sided PD.
authors.affiliation: Department of Neurology, Rambam Health Care Campus, Haifa, Israel; Laboratory of Clinical Neurophysiology, Faculty of Medicine, Technion, Haifa, Israel.
authors.forename: Y
authors.initials: Y
authors.lastname: Granovsky
authors.forename: I
authors.initials: I
authors.lastname: Schlesinger
authors.forename: S
authors.initials: S
authors.lastname: Fadel
authors.forename: I
authors.initials: I
authors.lastname: Erikh
authors.forename: E
authors.initials: E
authors.lastname: Sprecher
authors.forename: D
authors.initials: D
authors.lastname: Yarnitsky
mesh_terms: D000368:Aged; D000978:Antiparkinson Agents / Q000009:adverse effects*; D005260:Female; D007839:Functional Laterality / Q000502:physiology*; D006801:Humans; D006930:Hyperalgesia / Q000139:chemically induced* / Q000503:physiopathology; D007980:Levodopa / Q000009:adverse effects; D008297:Male; D008875:Middle Aged; D010146:Pain; D010147:Pain Measurement; D058748:Pain Perception / Q000187:drug effects* / Q000502:physiology; D017288:Pain Threshold / Q000187:drug effects / Q000502:physiology; D010300:Parkinson Disease / Q000188:drug therapy / Q000503:physiopathology*; D011601:Psychophysics
chemical_list: D000978:Antiparkinson Agents; D007980:Levodopa
keywords: Parkinson's disease; conditioned pain modulation; mesolimbic system; pain