title: Slow temporal summation of pain for assessment of central pain sensitivity and clinical pain of fibromyalgia patients.
abstract: BACKGROUND
  In healthy individuals slow temporal summation of pain or wind-up (WU) can be evoked by repetitive heat-pulses at frequencies of ≥.33 Hz. Previous WU studies have used various stimulus frequencies and intensities to characterize central sensitization of human subjects including fibromyalgia (FM) patients. However, many trials demonstrated considerable WU-variability including zero WU or even wind-down (WD) at stimulus intensities sufficient for activating C-nociceptors. Additionally, few WU-protocols have controlled for contributions of individual pain sensitivity to WU-magnitude, which is critical for WU-comparisons. We hypothesized that integration of 3 different WU-trains into a single WU-response function (WU-RF) would not only control for individuals' pain sensitivity but also better characterize their central pain responding including WU and WD.
  
  
  METHODS
  33 normal controls (NC) and 38 FM patients participated in a study of heat-WU. We systematically varied stimulus intensities of.4 Hz heat-pulse trains applied to the hands. Pain summation was calculated as difference scores of 1st and 5th heat-pulse ratings. WU-difference (WU-Δ) scores related to 3 heat-pulse trains (44°C, 46°C, 48°C) were integrated into WU-response functions whose slopes were used to assess group differences in central pain sensitivity. WU-aftersensations (WU-AS) at 15 s and 30 s were used to predict clinical FM pain intensity.
  
  
  RESULTS
  WU-Δ scores linearly accelerated with increasing stimulus intensity (p<.001) in both groups of subjects (FM>NC) from WD to WU. Slope of WU-RF, which is representative of central pain sensitivity, was significantly steeper in FM patients than NC (p<.003). WU-AS predicted clinical FM pain intensity (Pearson's r = .4; p<.04).
  
  
  CONCLUSIONS
  Compared to single WU series, WU-RFs integrate individuals' pain sensitivity as well as WU and WD. Slope of WU-RFs was significantly different between FM patients and NC. Therefore WU-RF may be useful for assessing central sensitization of chronic pain patients in research and clinical practice.
authors.affiliation: Department of Medicine, University of Florida, Gainesville, Florida, United States of America.
authors.forename: Roland
authors.initials: R
authors.lastname: Staud
authors.affiliation: Department of Medicine, University of Florida, Gainesville, Florida, United States of America.
authors.forename: Elizabeth E
authors.initials: EE
authors.lastname: Weyl
authors.affiliation: Department of Community Dentistry & Behavioral Science, University of Florida, Gainesville, Florida, United States of America.
authors.forename: Joseph L
authors.initials: JL
authors.lastname: Riley
authors.affiliation: Department of Community Dentistry & Behavioral Science, University of Florida, Gainesville, Florida, United States of America.
authors.forename: Roger B
authors.initials: RB
authors.lastname: Fillingim
mesh_terms: D000704:Analysis of Variance; D016022:Case-Control Studies; D005356:Fibromyalgia / Q000503:physiopathology*; D006358:Hot Temperature; D006801:Humans; D008954:Models, Biological; D009619:Nociceptors / Q000502:physiology*; D010146:Pain / Q000503:physiopathology*; D010147:Pain Measurement / Q000379:methods*; D011795:Surveys and Questionnaires