title: Characterization and consequences of pain variability in individuals with fibromyalgia.
abstract: OBJECTIVE
  A growing body of evidence suggests that real-time electronic assessments of pain are preferable to traditional paper-and-pencil measures. We used electronic assessment data derived from a study of patients with fibromyalgia (FM) to examine variability of pain over time and to investigate the implications of pain fluctuation in the context of a clinical trial.
  
  
  METHODS
  The study group comprised 125 patients with FM who were enrolled in a randomized, placebo-controlled trial of milnacipran. Pain intensity levels were captured in real time by participants using electronic diaries. Variability in pain was assessed as the standard deviation of pain entries over time (pain variability index [PVI]).
  
  
  RESULTS
  Substantial between-subject differences in pain variability were observed (mean +/- SD PVI 1.61 +/- 0.656 [range 0.27-4.05]). The fluctuation in pain report was constant over time within individuals (r = 0.664, P < 0.001). Individuals with greater variability were more likely to be classified as responders in a drug trial (odds ratio 6.14, P = 0.006); however, this association was primarily attributable to a greater change in pain scores in individuals receiving placebo (r = 0.460, P = 0.02) rather than active drug (r = 0.09, P > 0.10).
  
  
  CONCLUSIONS
  Among individuals with FM, there were large between-subject differences in real-time pain reports. Pain variability was relatively constant over time within individuals. Perhaps the most important finding is that individuals with larger pain fluctuations were more likely to respond to placebo. It is not clear whether these findings are applicable only to patients with FM or whether they may also be seen in patients with other chronic pain conditions.
authors.affiliation: Chronic Pain and Fatigue Research Center, University of Michigan Medical Center, 24 Frank Lloyd Wright Drive, PO Box 385, Ann Arbor, MI 48106, USA. reharris@med.umich.edu
authors.forename: Richard E
authors.initials: RE
authors.lastname: Harris
authors.forename: David A
authors.initials: DA
authors.lastname: Williams
authors.forename: Samuel A
authors.initials: SA
authors.lastname: McLean
authors.forename: Ananda
authors.initials: A
authors.lastname: Sen
authors.forename: Michael
authors.initials: M
authors.lastname: Hufford
authors.forename: R Michael
authors.initials: RM
authors.lastname: Gendreau
authors.forename: Richard H
authors.initials: RH
authors.lastname: Gracely
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Clauw
mesh_terms: D003521:Cyclopropanes / Q000627:therapeutic use*; D003625:Data Collection; D005260:Female; D005356:Fibromyalgia / Q000150:complications / Q000188:drug therapy* / Q000503:physiopathology; D006801:Humans; D008297:Male; D016347:Medical Records Systems, Computerized; D008875:Middle Aged; D000078764:Milnacipran; D010146:Pain / Q000175:diagnosis* / Q000188:drug therapy / Q000209:etiology; D010147:Pain Measurement / Q000379:methods*; D015203:Reproducibility of Results; D017367:Selective Serotonin Reuptake Inhibitors / Q000627:therapeutic use*
chemical_list: D003521:Cyclopropanes; D000078764:Milnacipran; D017367:Selective Serotonin Reuptake Inhibitors