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Expectancy Effects on Pain Measurements Identify a Subgroup of FM Patients that Report Higher Levels of Symptomatology
D.J.
Clauw¹, F. Petzke, and R.H. Gracely²
Department of Medicine, Georgetown University Medical Center¹
and NIDR, National Institutes of Health, Bethesda², MD
INTRODUCTION: Fibromyalgia is characterized by chronic widespread pain, tenderness and increased sensitivity to various sensory stimuli. Some have suggested that hypervigilance or increased “expectancy,” and not physiological factors, may cause the change in somatosensory perception in this and related conditions. One method of assessing the role of expectancy in sensory testing paradigms is to present stimuli in both an ascending and random fashion. In ascending paradigms, where the individual can anticipate the next stimulus, expectancy is felt to play a role in symptom reporting, whereas this effect is eliminated in random paradigms.
HYPOTHESIS: The concurrent use of ascending and random testing paradigms will identify some FM subjects who over-report pain in ascending paradigms (relative to the value obtained in random testing), and these subjects will have certain psychological and clinical characteristics.
PROCEDURES: Pressure pain sensitivity was assessed in 42 patients with FM and 27 age and gender matched HC. Both ascending (0.45-kg increments up to 4.54 kg [ASC]) and random (7 stimuli repeated twice in random order [RAN] rectangular pressure stimuli to the thumbnails of 5-sec duration were used. Pain intensity (PI) was recorded with a combined numerical analog descriptor scale and reported as area under curve. Tenderness (dolorimetry [DM], clinical pain intensity (Short form McGill [MG]), depression (Beck depression inventory [BDI] and symptom report (Brief Symptom Inventory [BSI]) were assessed concurrently.
SUMMARY OF RESULTS: As a group both HC and FM were more sensitive to the random than to the ascending pressure stimuli (HC: 16.3±2.4 vs. 41.6±5.9 [±SEM], p<.0001 and FM: 52.5±5.0 vs. 72.0±4.6, p<0.0001). The ratio of RAN/ASC was significantly lower in the group of FM patients (1.64±0.2 vs. 3.78±0.8, p<.017) because of a subset of subjects with high expectancy (ASC>RAN). The FM patients were divided into two groups (RAN/ASC<1.1 = “high expectancy” [HE] and RAN/ASC>1.1 = “low expectancy [LE]). Only 9 (21%) had HE, and compared to the LE these subjects reported significantly more clinical pain (MG scales: p<0.04-.001), more tenderness (DM pain threshold: 1.07±0.13 vs. 1.5±.01, p<.012), and higher somatic depression scores (BDI: 9.2±1.3 vs. 5.9±0.6, p<.02). BSI scores were not significantly different between HE and LE.
CONCLUSIONS: An increased pain response to the ascending (relative to the random) testing paradigm identifies a subgroup of FM patients with more severe disease, and/or an increased tendency to report pain and/or symptoms. These findings need to be extended and tested in the general population.
KEYWORDS: Pain, sensory, psychological
Individuals performing this study were supported in part by DAMD grants 17-96-1-6042 and 17-97-1-7361, and the Veteran’s Administration.Presented at the National Fibromyalgia Research Association's Subgroups in Fibromyalgia Symposium, September 26-27, 1999, in Portland, Oregon.
National Fibromyalgia
Research Association
PO Box 500, Salem, OR 97302
