Are patients with chronic pain and fibromyalgia correctly classified by MMPI-2 validity scales and indexes?

A study was designed to find out whether MMPI-2 validity scales and indexes differentiate between true fibromyalgia sufferers, patients with chronic organic pain and normal people, as well as whether they are correctly classified. 105 subjects participated in the study, 27 diagnosed with fibromyalgia and 44 with chronic organic pain and 34 were healthy people, who answered the MMPI-2 following standard instructions. The results showed that fibromyalgia patients scored higher than the control group in the F, Fb, F-K, Fp, Ds, and FBS scales and indexes and that patients with chronic organic pain scored higher in the Ds and FBS scales than the control group. The case study revealed that the F, Fb, F-K, Fp, Ds, and FBS scales and indexes over-diagnose malingering in patients with fibromyalgia, both in comparison with the clinical population and with the normative group. Likewise, patients with chronic organic pain were overdiagnosed as malingerers by all the scales and indexes in comparison with the normative population and by the Fp and FBS scales in comparison with the clinical population. In addition, it was found that at least one of the scales for measuring defensiveness –L, Wsd and Mp– classified 79.5% of the truly ill patients as faking good. The implications for clinical and forensic practice are discussed, as well as for the definition of decision criteria and the (re)classification as true negatives of genuine cases classified as malingerers by the malingering measuring scales and indexes.