Measuring Change in Fibromyalgic Pain: The Relevance of Pain Distribution

Abstract

Objectives: Though being a main characteristic of the syndrome, pain distribution has seldom been used as outcome measure in fibromyalgia. The present study aims at comparing the psychometric properties of a pain distribution measure with the visual analog scale [VAS] on pain, dolorimetry of tender points, and answers from an open-ended question on symptom improvement.

Methods: Pain distribution was assessed by a patient-made drawing, and quantified using Wallace's “rule of nine.” The four pain measures were used simultaneously in a repeated measurement design to assess treatment response in 48 fibromyalgia patients completing four months of either aerobic exercise, stress management or treatment-as-usual [control group].

Results: All measures were able to differentiate significantly between treatment and control conditions. A categorical factor analysis showed their change-scores to be valid in the sense that they all measured the same dimension. The open-ended question proved to be the most reliable measure, followed by the pain drawing and the VAS. The dolorimeter appeared to have considerable measurement error and low reliability when being used in a repeated measurement design. Only the pain drawing was significantly related to patients' own experience of pain variation, as assessed by the open-ended question.

Conclusion: Pain distribution seems to be an appropriate outcome measure in fibromyalgia, and its use is encouraged in future treatment research as are the use of an open-ended question and the VAS. However, the utility of dolorimeter scores from fibromyalgic tender points as a measure to assess change, is questioned.

KEYWORDS:

• Fibromyalgia
• pain measurement
• pain drawing
• pain threshold
• visual analog
• pain scale