Pain in fibromyalgia and discrimination power of the instruments: Visual Analog Scale, Dolorimetry and the McGill Pain Questionnaire.

Objective: The aim of this study was to verify the discriminative power of the most widely used pain assessment instruments.

Methods: The sample consisted of 279 subjects divided into Fibromyalgia Group FM- 205 patients with fibromyalgia and Control Group CG-74 healthy subjects), mean age 49.29 +/- 10.76 years. Only 9 subjects were male, 6 in FM and 3 in CG. FM were outpatients from the Rheumatology Clinic of the University of São Paulo--Hospital das Clínicas (HCFMUSP); the CG included people accompanying patients and hospital staff with similar socio-demographic characteristics. Three instruments were used to assess pain: the McGill Pain Questionnaire MPQ, the Visual Analog Scale (VAS), and the Dolorimetry, to measure pain threshold on tender points (generating the TP index). In order to assess the discriminative power of the instruments the measurements obtained were submitted to descriptive analysis and inferential analysis using ROC Curve-sensibility (S), specificity (S1) and area under the curve (AUC)--and Contingence tables with Chi-square Test and odds ratio. Significance level was 0.05.

Results: Higher sensibility specificity and area under the curve was obtained by VAS (80% 80% and 0.864, respectively), followed by Dolorimetry (S 77% S177% and AUC 0.851), McGill Sensory (S 72% S167% and AUC 0.765) and McGill Affective (S 69% S1 67% and AUC 0.753).

Conclusions: VAS presented the higher sensibility, specificity and AUC, showing the greatest discriminative power among the instruments. However, these values are considerably similar to those of Dolorimetry.