14. Quantitative Sensory Testing in Females with Endometriosis and Chronic Pelvic Pain

Abstract

Background

Chronic pelvic/abdominal pain (CPP) due to endometriosis can be unresponsive to standard therapies due to excessive sensitivity to pain known as central sensitization. We studied whether quantitative sensory testing (QST), a psychophysical method examining how the somatosensory nervous system responds to stimuli, differed between females with endometriosis and pain-free individuals.

Methods

Females with laparoscopically-confirmed endometriosis and CPP despite hormonal medication use (pain ≥3/ 0-10 scale, ≥14 days/mo) were eligible, and underwent baseline QST for an IRB-approved, multi-site clinical trial. We measured pressure pain threshold (minimum pressure evoking pain) using an algometer, and wind-up temporal summation (perception of pain due to repetitive equally intense stimuli) using electronic Von Frey, in the lower abdomen and control areas (non-dominant third finger nailbed/deltoid). Age-matched data from 107 pain-free females were used as a reference sample. Unadjusted statistical comparisons were conducted using the Mann–Whitney U test. Statistical models with adjustments for age, race, and BMI were developed to examine statistical differences in pain outcomes. Data are reported as median (interquartile range).

Results

We enrolled n=85 females with endometriosis (age: 25.3 (13.4)y). Our pain-free cohort included n=107 females (age: 20 (30.0)y; Table 1). Females with endometriosis experienced median (IQR) 3(3) intensity pain, >1 day/week, had lower median pain pressure thresholds (7.4 (8.1)) than the pain-free sample (16.0 (12.9); p< 0.01 based on unadjusted comparisons), and higher median temporal summation of pain (2.0 (2.5) vs. 0.5 (1.0); p< 0.01). These differences remained in adjusted analyses: lower pressure-pain thresholds (regression coefficient (β)=-0.28, 95% confidence interval (CI)= [-0.39, -0.18]) and higher temporal summation (β=1.69, 95% CI= [1.06, 2.31]). In females with endometriosis, median pressure pain threshold was lower on the abdomen compared with the finger (7.4 (8.1) vs. 17.1 (14.7), p< 0.01). No site difference (abdomen vs. deltoid) in temporal summation was estimated (p=0.15).

Conclusions

Females with endometriosis had lower pressure-pain thresholds, indicating higher sensitivity to pain, and higher temporal summation measures, reflecting greater increase in pain perception from exposure to repetitive stimuli, compared with pain-free females. The pressure-pain threshold was lower at the lower abdomen vs. finger in those with endometriosis, but temporal summation was the same. Clinicians should consider treatments aimed at reducing central sensitization to pain in those with CPP due to endometriosis.