Multimodal nociceptive mechanisms underlying chronic pelvic pain

To evaluate candidate mechanisms underlying the pelvic floor dysfunction in women with chronic pelvic pain and/or painful bladder syndrome/interstitial cystitis. Notably, prior studies have not consistently controlled for potential confounding by psychological or anatomical factors.

As part of a larger study on pelvic floor pain dysfunction and bladder pain sensitivity, we compared a measure of mechanical pain sensitivity, pressure pain thresholds, between women with pelvic pain and pain-free controls. We also assessed a novel pain measure using degree and duration of post-exam pain aftersensation, and conducted structural and functional assessments of the pelvic floor to account for any potential confounding. Phenotypic specificity of pelvic floor measures was assessed with receiver-operator characteristic curves adjusted for prevalence.

A total of 23 women with chronic pelvic pain, 23 painful bladder syndrome, and 42 pain-free controls completed the study. Women with chronic pelvic pain or painful bladder syndrome exhibited enhanced pain sensitivity with lower pressure pain thresholds (1.18 [interquartile range: 0.87-1.41] kg/cm2) than pain-free participants (1.48 [1.11-1.76] kg/cm2; p<0.001) and prolonged pain aftersensation (3.5 [0-9] vs 0 [0-1] minutes; p< 0.001). Although genital hiatus (p<0.01) was wider in women with chronic pelvic pain there were no consistently observed group differences in pelvic floor anatomy, muscle tone or strength. The combination of pressure pain thresholds and aftersensation duration correlated with severity of pelvic floor tenderness (R2 =41-51, p's< 0.01). Even after adjustment for prevalence, the combined metrics discriminated pain-free controls from women with chronic pelvic pain or painful bladder syndrome (area under the curve=0.87).

Both experimental assessment of pelvic floor pain thresholds and measurement of sustained pain are independently associated with pelvic pain phenotypes. These findings suggest systematic clinical assessment of the time course of provoked pain symptoms, which occurs over seconds for mechanical pain thresholds vs. minutes for aftersensation pain, would be helpful in identifying the fundamental mechanisms of pelvic floor pain. Longitudinal studies of therapies differentially targeting these discrete mechanisms are needed to confirm their clinical significance.

American journal of obstetrics and gynecology 2015 Aug 20 [Epub ahead of print]

Kevin M Hellman, Insiyyah Y Patanwala, Kristen E Pozolo, Frank F Tu

Department of Obstetrics and Gynecology, University of Chicago Medical Center, Chicago, IL, USA; Department of Obstetrics and Gynecology, NorthShore University HealthSystem, Evanston, IL, USA; University of Chicago, Pritzker School of Medicine, Chicago, IL, USA , Department of Obstetrics and Gynecology, University of Chicago Medical Center, Chicago, IL, USA; Department of Obstetrics and Gynecology, NorthShore University HealthSystem, Evanston, IL, USA , Department of Obstetrics and Gynecology, NorthShore University HealthSystem, Evanston, IL, USA , Department of Obstetrics and Gynecology, University of Chicago Medical Center, Chicago, IL, USA; Department of Obstetrics and Gynecology, NorthShore University HealthSystem, Evanston, IL, USA; University of Chicago, Pritzker School of Medicine, Chicago, IL, USA  

PubMed

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