Assessing fibromyalgia-related fatigue: content validity and psychometric performance of the Fatigue Visual Analog Scale in adult patients with fibromyalgia

Clin Exp Rheumatol. Nov-Dec 2011;29(6 Suppl 69):S34-43. Epub 2012 Jan 3.

Abstract

Objectives: To document 1) the content validity and 2) measure improvements in fatigue, using the Fatigue Visual Analogue Scale (VAS) assessment tool in patients with fibromyalgia.

Methods: The relevance and comprehensiveness of the Fatigue VAS were tested through a qualitative analysis of 20 subjects' verbatim transcripts from semi-structured qualitative interviews. Data from two randomised, controller trials in fibromyalgia (n=1121) were used to conduct correlation analyses with the Fatigue and Tiredness items from the Fibromyalgia Impact Questionnaire (FIQ) and the Short Form-36 Vitality scale. Known-groups and cross classification analyses were conducted to demonstrate the ability to measure improvement in fatigue using the Fatigue VAS.

Results: All subjects spontaneously reported that fatigue was an important symptom to capture in fibromyalgia. The Fatigue VAS was well understood by most subjects (n=18/20). High correlations (Pearson r>0.75) and good agreement (k>0.66) were found between the Fatigue VAS and the FIQ tiredness items no. 16 and 17 and SF-36™ Vitality scale. In both clinical trials there was a substantial separation of approximately 20 points on the mean change in the Fatigue VAS score between responders (>30% improvement in pain VAS) and non-responders.

Conclusions: Previous studies have confirmed that fatigue is a major component of the fibromyalgia experience. This current study reports that fibromyalgia patients spontaneously rated fatigue as a highly significant feature of their illness, and supports the use of the Fatigue VAS as a valid questionnaire in fibromyalgia clinical trials.

Publication types

  • Randomized Controlled Trial
  • Research Support, Non-U.S. Gov't
  • Validation Study

MeSH terms

  • Adult
  • Aged
  • Analgesics / therapeutic use
  • Chronic Pain / diagnosis*
  • Chronic Pain / drug therapy
  • Chronic Pain / physiopathology
  • Chronic Pain / psychology
  • Fatigue Syndrome, Chronic / diagnosis*
  • Fatigue Syndrome, Chronic / drug therapy
  • Fatigue Syndrome, Chronic / physiopathology
  • Fatigue Syndrome, Chronic / psychology
  • Female
  • Fibromyalgia / diagnosis*
  • Fibromyalgia / drug therapy
  • Fibromyalgia / physiopathology
  • Fibromyalgia / psychology
  • Health Status
  • Humans
  • Interviews as Topic
  • Male
  • Middle Aged
  • Pain Measurement
  • Psychometrics / methods*
  • Sickness Impact Profile
  • Sodium Oxybate / therapeutic use
  • Syndrome

Substances

  • Analgesics
  • Sodium Oxybate