Background: Fibromyalgia (FM) is classified by the presence of generalized spontaneous pain and increased pressure pain sensitivity. Psychophysical studies have shown mostly normal perception thresholds for various sensory modalities but lowered thresholds for painful or aversive stimulation. This has been explained by central augmentation of pain processing and psychological factors such as hypervigilance. However, these studies used various methodological approaches and small sample sizes limiting comparability between studies and different patient populations. In addition, relevant subgroups of patients with FM have been described with differences in pressure pain sensitivity (1).
Objectives: In this study we used the standardized quantitative sensory testing protocol of the German Research Network on Neuropathic Pain (DFNS)(2) to evaluate thermal and mechanical sensory perception in patients with FM.
Methods: 82 female patients with FM and 38 age matched controls (HC) were included (FM:55.5±8.5 vs. HC: 53.7±8.9, p=n.s.). Patients had discontinued and washed out pain relevant medications and had normal clinical neurological exams. Patients with relevant concomittant diseases were excluded. Quantitative Sensory Testing (QST) was performed on the right hand following (1). Thermal detection and pain thresholds including paradoxical heat senstations, mechanical detection thresholds to van Frey filaments and a 64 Hz tuning fork, mechanical pain threshold to pin prick stimuli and blunt pressure, stimulus-response functions to pin prick and dynamic mechanical allodynia and pain summation to pin prick stimulation were determined. Data on psychological and functional status was obtained by various questionnaires (SF-36, BDI, CSQ, STAI, and SF-McGill). All data are mean±SEM.
Results: Thermal testing in patients with FM showed normal cold and warm detection thresholds when compared to heabthy controls and no paradoxical heat sensations. But both cold and heat pain thresholds were significantly lower in FM (cold: 16.5±1.0 vs. 8.9±1.2 °C, p<0.001; heat: 41.9±0.4 vs. 45.1±0.5 °C, p<0.001). Mechanical testing reveled slightly increased mechanical detection thresholds in FM compared to HC(2.4±0.2 vs. 1.17±0.4 mN, p<0.001). Mechanical pain thresholds were decreased in patients with FM both to pin prick stmulation (37.1±0.3 vs. 61.9±0.4 mN, p<0.01) and blunt pressure (271±16 vs. 467±19 kPa, p<0.0001). There was no mechanical dynamic allodynia in FM and no difference in the stimulus-response function and vibration thresholds between FM and HC. Pain summation was, however, increased in FM (p<0.05).

Conclusion: This study using the QST protocol by the DFNS replicates several of the previous findings. There is no evidence for a generalized hypervigilance to somatosensory stimuli in FM but for a more differentiated profile. Potential mechanisms include dereased descending inhibition or increased faciliation of painful stimuli. The protocol used in this study will enable the comparison of subgropus of patients with FM, but also with other patient groups with disturbed sensory processing of various somatic, functional and psychological aetiologies.
References: (1) Giesecke T. et al. Arthritsi and Rheumatism 48 (2003) 2916-2923. (2) Rolke R. et al.. Pain 123 (2006) 231-243.