Interstitial cystitis/bladder pain syndrome (IC/BPS) patients may experience pelvic floor muscle (PFM) overactivity at rest concomitantly which can be objectively measured with intravaginal high-density surface electromyography (HD-sEMG). This PFM overactivity at rest in IC/BPS patients has been associated with an altered and elevated level of neural drive to the PFM. Furthermore, IC/BPS patients also report variable locations and pain severity pelvic and widespread non-pelvic pain. However, the relationship between these pain factors and PFM overactivity at rest remains poorly understood. In this study we investigated the relationship of PFM overactivity at rest with the widespreadness of patient-reported pain in female IC/BPS patients. This is the first study to analyze PFM overactivity at rest while grouping patients according to the widespreadness of their pain. We hypothesize that patients with more widespread pain will present with higher PFM overactivity at rest.

Fifteen healthy women without IC/BPS and fifteen women diagnosed with IC/BPS, all above the age of 18 years old, were recruited to participate in the study with written consent. The justification of a sample size of fifteen participants per group is based on recent literature that assessed aspects of PFM hypertonicity and observed significance [1]. While IC/BPS patients are inherently heterogenous in nature with varying underling etiology and pathophysiology we have enriched the patient samples by only including patients with concomitant PFM tenderness who are more likely to have electromyographic abnormalities. HD-sEMG was recorded from fifteen women with IC/BPS and fifteen female healthy controls before and during maximal voluntary force PFM contractions. The root-mean-squared (RMS) amplitude of HD-sEMG at rest was normalized to the maximal RMS amplitude during contraction to produce RMS ratios [2] and grouped according to reported widespreadness of pain according to the body-pain maps used in a previous Multidisciplinary Approach to the Study of Chronic Pelvic Pain (MAPP) Research Network study [3] (Fig. 1). (None, Pelvic Only, Intermediate, and Widespread). The “None” group (N=15) reported no locations of pain. The “Pelvic Only” (N=6) group reported pain at the abdomen and pelvis only. The “Intermediate” group (N=4) reported one or two extra areas of pain outside the pelvis. The “Widespread” group (N=5) reported three to seven further areas of pain outside the pelvis. Healthy female controls composed the “None” group. Spearman’s rank correlation was used to assess the strength of association between the RMS ratios and total number of reported pain locations from the body-pain maps. In a secondary, exploratory analysis, RMS ratios were compared across pain type groups via One-Way Analysis of Variance (ANOVA), after confirming normality with Anderson-Darling tests. Multiple-comparisons tests were performed with the Tukey-Kramer test.

(1)	RMS ratios are positively correlated with the widespreadness of pain (r=0.5093; p=0.004)
(2)	RMS ratios of healthy female controls with no pain are significantly lower than female IC/BPS patients reporting widespread pain (p=0.003) (Fig. 2)

As hypothesized, the magnitude of RMS ratios increased along with the number of reported locations of pain outside the pelvis, or pain widespreadness. Specifically, significant differences in RMS ratios were observed between healthy female controls with no pain and female IC/BPS patients with widespread pain. However, no other between-group differences were observed. This may in part be due to the reduced sample size of the total IC/BPS sample when grouping patients by pain widespreadness. Additionally, the presence of exceptionally high PFM overactivity at rest for the female IC/BPS patients with widespread pain but not lesser widespreadness of pain may suggest that a certain vastness of pain is necessary before observing such alterations in neural drive as suggested by electromyogram signal amplitude at rest. The degree of PFM overactivity at rest identified in female IC/BPS patients with widespread pain may be associated with central sensitization. Alternatively, the greater widespreadness of pain may cause female IC/BPS patients to engage in muscle guarding.

As a previous study determined, the widespreadness of pain reported by IC/BPS patients is not significantly associated with worsening pelvic pain symptoms [3]. However, a trend was identified in this study for PFM overactivity at rest to increase with the widespreadness of pain. These two observations may provide increasing support for the concurrent study of pelvic and non-pelvic muscles as they relate to PFM overactivity in IC/BPS patients.

Female IC/BPS patients experiencing widespread pain outside the pelvis may be more likely to experience greater PFM overactivity at rest. These results reinforce the heterogenous nature of IC/BPS and suggest that patients with more severe PFM overactivity at rest may have centralized pain or more widespread pain.

Ackerman, A. Lenore, et al. "MRI suggests increased tonicity of the levator ani in women with interstitial cystitis/bladder pain syndrome." International urogynecology journal 27 (2016): 77-83.
Dias, Nicholas, et al. "High-density surface electromyography assessment of pelvic floor dysfunction in women with interstitial cystitis/bladder pain syndrome." The Journal of urology 204.6 (2020): 1275-1283.
Lai, H. Henry, et al. "Characterization of whole body pain in urological chronic pelvic pain syndrome at baseline: a MAPP research network study." The Journal of urology 198.3 (2017): 622-631.

Continence 7S1 (2023) 100822
DOI: 10.1016/j.cont.2023.100822