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

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.