title: Placebo response changes depending on the neuropathic pain syndrome: results of a systematic review and meta-analysis.
abstract: OBJECTIVE
  To compare placebo responses in neuropathic pain syndromes.
  
  
  METHODS
  Systematic literature review and meta-analysis.
  
  
  METHODS
  Randomized placebo-controlled trials assessing pain intensity or pain relief in any neuropathic pain syndrome published since 1995 with ≥5days follow-up.
  
  
  METHODS
  Placebo response.
  
  
  METHODS
  Pain intensity and responder rates (proportion reporting ≥50% pain relief). Meta-regression models were built.
  
  
  RESULTS
  Ninety-four studies (N=5,317) were included in the pain intensity analysis; 47 studies (N=3,087) were included in the responder analysis. After controlling for potential confounders (e.g., subject characteristics, study design characteristics), the placebo response was found to be large and varied with the pain syndrome. Compared with diabetic neuropathic/polyneuropathic pain (DPN), the placebo response for a decline in pain intensity and responder rate was smaller in trials that assessed central pain and postherpetic neuralgia (PHN) and larger in trials that assessed HIV pain. The model-predicted mean decrease (95% confidence interval [CI]) from baseline in pain intensity (0-10 scale) was as follows: DPN, 1.45 (1.35 to 1.55); PHN, 1.16 (1.03 to 1.29); central pain, 0.44 (-0.41 to 1.30); HIV pain, 1.82 (1.51 to 2.12). The predicted responder rates (95% CI) were as follows: DPN, 20% (14.6 to 25.8); PHN, 11.5% (8.4 to 14.5); central pain, 7.2% (2.1 to 12.3); HIV pain, 42.8% (34.9 to 50.7). The type of treatment in the active arm also influenced the placebo response.
  
  
  CONCLUSIONS
  Placebo response is influenced by the pain syndrome evaluated. These differences should be considered when evaluating novel compounds for the treatment of neuropathic pain conditions.
authors.affiliation: Janssen Research and Development, L.L.C., Titusville, New Jersey 08560, USA. scepeda@its.jnj.com
authors.forename: M Soledad
authors.initials: MS
authors.lastname: Cepeda
authors.forename: Jesse A
authors.initials: JA
authors.lastname: Berlin
authors.forename: C Yuying
authors.initials: CY
authors.lastname: Gao
authors.forename: Frank
authors.initials: F
authors.lastname: Wiegand
authors.forename: D Russell
authors.initials: DR
authors.lastname: Wada
mesh_terms: D003929:Diabetic Neuropathies / Q000175:diagnosis / Q000188:drug therapy / Q000523:psychology; D006801:Humans; D009437:Neuralgia / Q000175:diagnosis / Q000188:drug therapy* / Q000523:psychology*; D051474:Neuralgia, Postherpetic / Q000175:diagnosis / Q000188:drug therapy / Q000517:prevention & control; D058748:Pain Perception / Q000187:drug effects / Q000502:physiology*; D010919:Placebos / Q000494:pharmacology*; D016032:Randomized Controlled Trials as Topic
chemical_list: D010919:Placebos