Fibromyalgia: Can one distinguish it from simulation? An observer-blind controlled study

Objective. A randomized controlled trial was conducted to assess reliabilit y and accuracy in identification of fibromyalgia (FM), motivated simulation , and normal controls. Methods. Eight female subjects with chronic FM were age matched with 19 hea lthy female volunteers. The volunteers were randomized to a financially mot ivated "simulator" group who were paid to simulate FM, or to a "normal cont rol" group, Examiners under blinded conditions rated tender and control poi nts, and illness behavior. Intraclass correlation coefficients and F values showed that counts of tender points significantly discriminated the 3 grou ps. Variance was mostly due to experimental groups and not to observer or e rror factors. Ln this study, simulators could not be discriminated from nor mals or FM subjects on the basis of tenderness at "control points." Examine r ratings of illness behavior (UAB), and subjects' self-ratings for pain sh owed that FM subjects had the highest scores, normals the lowest, and simul ators had mean scores midway between the mean FM and simulator. On grip str ength, the normals obtained the highest scores, the simulators the lowest, and the FM subjects had scores midway between those of the other 2 groups. Diagnostic accuracy of the blinded examiners in distinguishing FM from simu lators and from normals was 80%, and for correct diagnosis the kappa value was significant at 0.69. Despite this, simulators were misidentified as FM in 1/3 of judgments, and FM was misidentified as simulators in 1/5 of judgm ents. Conclusion. Under randomized blinded conditions, examiners using the Americ an College of Rheumatology criteria for FM and other bedside observations a re able to distinguish chronic FM, normal individuals, and motivated simula tors with 80% accuracy, with a good level of agreement and reliability in t ender point counts. Our results do not provide a "test for malingering," an d it is likely that an important minority of motivated simulators and of FM subjects will be misidentified.