Diffuse noxious inhibitory control function in women with provoked vestibulodynia

Provoked Vestibulodynia (PVD), the most common form of chronic genital pain affecting 12% of women in the general population, is characterized by a severe burning pain in response to pressure to the vaginal entrance. Research indicates that women with PVD display similar responses as individuals with other chronic pain conditions (i.e., heightened sensitivity to both painful and non-painful stimuli in affected and non-affected areas). This increased pain sensitivity has been demonstrated in other chronic pain conditions to be due, in part, to impairment in centrally acting endogenous pain modulation systems, such as Diffuse Noxious Inhibitory Control (DNIC). DNIC is triggered by the simultaneous application of two painful stimuli, with pain at one body site inhibiting pain at a distal body site. The major aim of this research was to investigate DNIC function in women with PVD. Twenty women with PVD and 24 controls underwent thermal sensory testing to determine the integrity of DNIC function. Participants underwent three trials of testing for heat pain tolerance on the forearm before, during, and after immersion of the opposite arm in a cold water bath. When DNIC was measured by temperature change, there was no significant difference between groups in terms of number of women with an intact DNIC response (Control N = 79%; PVD N = 80%), t(42) = -.07, ns. However, when measured by subjective pain ratings, 75% of control women and only 45% of women with PVD had an intact DNIC response, resulting in a significant difference between groups, t(42) = 2.06, p < .05. Results will be discussed in terms of discrepant findings between psychophysical and subjective ratings and the implications this holds for future research in the areas of chronic pain and PVD. (Supported by a grant from the Canadian Institutes of Health Research)