Study of experimental pain measures and nociceptive reflex in chronic pain patients and normal subjects

This study evaluates (i) the effect of heterotopic chronic pain on various experimental pain measures, (ii) the relationship between experimental pain measures and chronic pain symptomatology assessment, and (iii) the influence of the various pain aetiologies on experimental pain measures. Fifty-three chronic pain patients were compared to 17 pain-free subjects with the following psychophysical and physiological indices: pain threshold (PTh), pain tolerance (PTol), verbal estimation of intensity and unpleasantness (intensity scale, IS; unpleasantness scale, US), threshold for intensity and unpleasantness (ITh and UTh), lower limb RIII nociceptive reflex (RIIITh and RIII frequency of occurrence). Chronic pain syndromes included neuropathic pain (n = 12), iodopathic pain (n = 12), myofascial syndromes (n = 9), headache (n = 9), and miscellaneous pain (n = 11). Chronic pain symptomatology was assessed with a visual analogue scale (VAS), a French MPQ adaptation (QDSA), Beck Depression Inventory (BDI), Spielberger State Trait Inventory (STAI) and Eysenck Personality Inventory (EPI). No significant difference was observed between chronic pain patients and pain-free control groups and between patient subgroups for PTh, PTol and RIIITh. No significant correlation was found between experimental pain measures and clinical pain, anxiety or depression scores. However, the chronic pain patients had a higher threshold for unpleasantness and judged the suprathreshold stimuli significantly less intense and less unpleasant than the control group. These results are discussed in relation to diffuse noxious inhibitory controls and the adaptation level theory of chronic pain experience.