title: Impaired modulation of pain in patients with postherpetic neuralgia.
abstract: BACKGROUND
  The efficiency of inhibitory pain descending pathways (evaluated using conditioned pain modulation [CPM]) has not been studied in postherpetic neuralgia (PHN).
  
  
  OBJECTIVE
  To compare CPM in PHN patients with healthy controls.
  
  
  METHODS
  Nine PHN patients and nine control individuals were matched according to age and sex. Amplitudes of cortical thermal-evoked potentials were recorded on the surface of the scalp; clinical pain and thermal pain were evaluated on a 0 to 10 numerical rating scale, at baseline and at intervals during the 6 min after CPM (elicited by a cold pressor test, 8°C). A battery of cognitive tests was performed. Amplitude differences, percentages and related areas under the curve (AUC<span style="vertical-align: sub">CPM<⁄span>) were calculated and all data were compared between both groups; P<0.05 was considered to be statistically significant.
  
  
  RESULTS
  AUC<span style="vertical-align: sub">CPM0-6 min<⁄span> was significantly lower in PHN patients compared with controls (-39±51 µV⁄min versus -144±66 µV⁄min; P=0.0012) and correlated (P=0.04) with clinical pain intensity. Pain ratings before CPM were similar in both groups but were significantly lower in the control group 3 min after the cold pressor test. Cognitive test results were not significantly different.
  
  
  CONCLUSIONS
  Psychophysical and electrophysiological approaches have shown that patients with PHN exhibit a deficiency of pain inhibition modulation, which could signal a predisposing factor to developing chronic pain. This deficiency was not linked to the cognitive performance but rather to subtle in situ cognitivoemotional adaptations, which remain to be investigated.
authors.forename: Gisele
authors.initials: G
authors.lastname: Pickering
authors.forename: Bruno
authors.initials: B
authors.lastname: Pereira
authors.forename: Elodie
authors.initials: E
authors.lastname: Dufour
authors.forename: Sylvie
authors.initials: S
authors.lastname: Soule
authors.forename: Claude
authors.initials: C
authors.lastname: Dubray
mesh_terms: D000368:Aged; D003080:Cold Temperature; D005071:Evoked Potentials; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D051474:Neuralgia, Postherpetic / Q000175:diagnosis* / Q000453:epidemiology*; D010146:Pain / Q000175:diagnosis / Q000453:epidemiology; D010147:Pain Measurement / Q000379:methods*; D011446:Prospective Studies; D011930:Reaction Time