Neurobiology and long-term impact of bladder-filling pain in humans: a Multidisciplinary Approach to the Study of Chronic Pelvic Pain (MAPP) research network study

ABSTRACT

Pain with bladder filling remains an unexplained clinical presentation with limited treatment options. Here, we aim to establish the clinical significance of bladder filling pain using a standardized test and the associated neural signature. We studied individuals diagnosed with urologic chronic pelvic pain syndrome (UCPPS) recruited as part of the multidisciplinary approach to the study of chronic pelvic pain (MAPP) study. Patients with urologic chronic pelvic pain syndrome (N = 429) and pain-free controls (N = 72) underwent a test in which they consumed 350 mL of water and then reported pain across an hour-long period at baseline and 6 months. We used latent class trajectory models of these pain ratings to define UCPPS subtypes at both baseline and 6 months. Magnetic resonance imaging of the brain postconsumption was used to examine neurobiologic differences between the subtypes. Healthcare utilization and symptom flare-ups were assessed over the following 18 months. Two distinct UCPPS subtypes were identified, one showing substantial pain related to bladder filling and another with little to no pain throughout the test. These distinct subtypes were seen at both baseline and 6 month timepoints. The UCPPS subtype with bladder-filling pain (BFP+) had altered morphology and increased functional activity in brain areas involved in sensory and pain processing. Bladder-filling pain positive status predicted increased symptom flare-ups and healthcare utilization over the subsequent 18 months when controlling for symptom severity and a self-reported history of bladder-filling pain. These results both highlight the importance of assessing bladder filling pain in heterogeneous populations and demonstrate that persistent bladder-filling pain profoundly affects the brain.

Neurotrophins and Their Receptors, Novel Therapeutic Targets for Pelvic Pain in Endometriosis, Are Coordinately Regulated by IL-1β via the JNK Signaling Pathway

Pelvic pain in women with endometriosis is attributed to neuroinflammation and afferent nociceptor nerves in ectopic and eutopic endometrium. The hypothesis that uterine nociception is activated by IL-1β, a prominent cytokine in endometriosis, was tested herein. Immunofluorescence histochemistry confirmed the presence of neurons in human endometrial tissue. Expression of nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) and their receptors in endometrial tissue and cells was validated by immunohistochemistry and Western blotting. Isolated endometrial stromal cells (ESCs) were subjected to dose-response and time-course experiments with IL-1β and kinase inhibitors to characterize in vitro biomarkers. Neural biomarkers were co-localized in endometrial nerve fibers. NGF, BDNF, and their receptors tropomyosin receptor kinase (Trk) A, TrkB, and p75 neurotrophin receptor were all expressed in primary ESCs. IL-1β stimulated higher TrkA/B expression in ESCs derived from endometriosis cases (2.8- ± 0.2-fold) than cells from controls (1.5- ± 0.3-fold, t-test, P < 0.01), effects that were mediated via the c-Jun N-terminal kinase (JNK) pathway. BDNF concentrations trended higher in peritoneal fluid of endometriosis cases but were not statistically different from controls (P = 0.16). The results support the hypothesis that NGF and BDNF and their corresponding receptors orchestrate innervation of the endometrium, which is augmented by IL-1β. We postulate that JNK inhibitors, such as SP600125, have the potential to reduce neuroinflammation in women with endometriosis.

Reliability and Validity of Pain and Urinary Symptom Severity Assessment in Urological Chronic Pelvic Pain: A MAPP Network Analysis

PURPOSE

We assessed the reliability and validity of an efficient severity assessment for pelvic pain and urinary symptoms in urological chronic pelvic pain syndrome, which consists of interstitial cystitis/bladder pain syndrome and chronic prostatitis/chronic pelvic pain syndrome.

MATERIALS AND METHODS

A total of 578 patients were assessed using brief, empirically derived self-report scales for pelvic pain severity (PPS) and urinary symptom severity (USS) 4 times during a 1-month period and baseline clinic visit that included urological, pain and illness-impact measures. Mild, moderate and severe categories on each dimension were examined for measurement stability and construct validity.

RESULTS

PPS and USS severity categories had adequate reliability and both discriminant validity (differential relationships with specific clinical and self-report measures) and convergent validity (common association with nonurological somatic symptoms). For example, increasing PPS was associated with pelvic tenderness and widespread pelvic pain, whereas USS was associated with urgency during a bladder filling test and increased sensory sensitivity. PPS and USS categories were independently associated with nonurological pain and emotional distress. A descriptive analysis identified higher likelihood characteristics associated with having moderate to severe PPS or USS or both. Lack of sex interactions indicated that the measures are comparable in interstitial cystitis/bladder pain syndrome and chronic prostatitis/chronic pelvic pain syndrome.

CONCLUSIONS

Women and men with urological chronic pelvic pain syndrome can be reliably subgrouped using brief self-report measures of mild, moderate or severe pelvic pain and urinary symptoms. Comparisons with a broad range of clinical variables demonstrate the validity and potential clinical utility of these classifications, including use in clinical trials, health services and biological research.

Incidence and predictors of persistent pelvic pain following hysterectomy in women with chronic pelvic pain

BACKGROUND

Chronic pelvic pain is a debilitating problem that afflicts 15% to 20% of women in the United States. Although more than 200,000 hysterectomies are performed annually for the treatment of chronic pelvic pain, previous studies indicate that 1 in 4 women undergo the discomfort and morbidity of hysterectomy without the relief of pain. The factors that predict treatment failure remain poorly characterized.

OBJECTIVE

To describe the incidence of persistent pelvic pain 6 months following hysterectomy in women with chronic pelvic pain and determine whether a simple, self-reported measure of central sensitization is associated with a greater risk of persistent pelvic pain following hysterectomy.

STUDY DESIGN

We conducted a prospective, observational cohort study of women undergoing hysterectomy at an academic tertiary care center for a benign indication. Patients with preoperative chronic pelvic pain, defined as average pelvic pain ≥3 on a 0 to 10 numeric rating scale for >3 months before hysterectomy, were included in this analysis. The patients completed validated assessments of pain, anxiety, depression, and centralized pain (using the 2011 Fibromyalgia Survey Criteria, 0-31 points) preoperatively and 6 months after hysterectomy. The demographic information, surgical history, intraoperative findings, and surgical pathology were abstracted from the electronic medical records. Multivariate logistic regression was used to identify the independent predictors of persistent pelvic pain 6 months following hysterectomy, defined as <50% improvement in pelvic pain severity.

RESULTS

Among 176 participants with pelvic pain before hysterectomy, 126 (71.6%) were retained at 6 months, and 15 (11.9%) reported persistent pelvic pain. There was no difference in age (P=.46), race (P=.55), average pain severity during menses (P=.68), average overall pelvic pain (P=.10), or pain duration (P=.80) in those with and without persistent pelvic pain. Whereas intraoperative findings of endometriosis (P=.05) and uterine fibroids (P=.03) were associated with a higher incidence of persistent pain on univariate analysis, the surgical route (P=.46), pelvic adhesions (0.51), uterine weight (P=.66), and adenomyosis on histopathology (P=.27) were not related to the risk of persistent pain. Higher preoperative centralized pain scores (P=.01) but not depression (P=.64) or anxiety (P=.45) were more common in women with persistent pelvic pain. Multivariate logistic regression adjusting for age, preoperative pain severity, anxiety, depression, and operative findings of endometriosis and fibroids indicated that every 1-point increase in centralized pain before hysterectomy was associated with a 27% increase in the odds of persistent pelvic pain (odds ratio, 1.27; 95% confidence interval, 1.03-1.57) 6 months after surgery.

CONCLUSION

Although the majority of women with chronic pelvic pain report considerable improvement in pain following hysterectomy, higher degrees of centralized pain before hysterectomy is a robust predictor of persistent pelvic pain.

Stimulation of zona incerta selectively modulates pain in humans

Stimulation of zona incerta in rodent models has been shown to modulate behavioral reactions to noxious stimuli. Sensory changes observed in Parkinsonian patients with subthalamic deep brain stimulation suggest that this effect is translatable to humans. Here, we utilized the serendipitous placement of subthalamic deep brain stimulation leads in 6 + 5 Parkinsonian patients to directly investigate the effects of zona incerta stimulation on human pain perception. We found that stimulation at 20 Hz, the physiological firing frequency of zona incerta, reduces experimental heat pain by a modest but significant amount, achieving a 30% reduction in one fifth of implants. Stimulation at higher frequencies did not modulate heat pain. Modulation was selective for heat pain and was not observed for warmth perception or pressure pain. These findings provide a mechanistic explanation of sensory changes seen in subthalamic deep brain stimulation patients and identify zona incerta as a potential target for neuromodulation of pain.

The Multidisciplinary Approach to The Study of Chronic Pelvic Pain (MAPP) Research Network*: Design and implementation of the Symptom Patterns Study (SPS)

AIMS

The Multidisciplinary Approach to the Study of Chronic Pelvic Pain (MAPP) Research Network initiated a second observational cohort study-the Symptom Patterns Study (SPS)-to further investigate the underlying pathophysiology of Urologic Chronic Pelvic Pain Syndrome (UCPPS) and to discover factors associated with longitudinal symptom changes and responses to treatments.

METHODS

This multisite cohort study of males and females with UCPPS features a run-in period of four weekly web-based symptom assessments before a baseline visit, followed by quarterly assessments up to 36 months. Controls were also recruited and assessed at baseline and 6 months. Extensive clinical data assessing urological symptoms, nonurological pain, chronic overlapping pain syndromes, and psychosocial factors were collected. Diverse biospecimens for biomarker and microbiome studies, quantitative sensory testing (QST) data under multiple stimuli, and structural and functional neuroimaging scans were obtained under a standardized protocol.

RESULTS

Recruitment was initiated (July 2015) and completed (February 2019) at six discovery sites. A total of 620 males and females with UCPPS and 73 Controls were enrolled, including 83 UCPPS participants who re-enrolled from the first MAPP Network cohort study (2009-2012). Baseline neuroimaging scans, QST measures, and biospecimens were obtained on 578 UCPPS participants. The longitudinal follow-up of the cohort is ongoing.

CONCLUSIONS

This comprehensive characterization of a large UCPPS cohort with extended follow-up greatly expands upon earlier MAPP Network studies and provides unprecedented opportunities to increase our understanding of UCPPS pathophysiology, factors associated with symptom change, clinically relevant patient phenotypes, and novel targets for future interventions.