Is there a difference in pelvic floor muscle tone between women with and without pelvic pain? A systematic review and meta-analysis

Background
Alterations in pelvic floor muscle (PFM) function have been observed in women with persistent noncancer pelvic pain (PNCPP) as compared with women without PNCPP; however, the literature presents conflicting findings regarding differences in PFM tone between women with and without PNCPP.
Aim
To systematically review the literature comparing PFM tone in women with and without PNCPP.
Methods
MEDLINE, Embase, Emcare, CINAHL, PsycINFO, and Scopus were searched from inception to June 2021 for relevant studies. Studies were included that reported PFM tone data in women aged ≥18 years with and without PNCPP. The risk of bias was assessed with the National Heart, Lung, and Blood Institute Quality Assessment Tool. Standardized mean differences (SMDs) for PFM tone measures were calculated via random effects models.
Outcomes
Resting PFM tone parameters, including myoelectrical activity, resistance, morphometry, stiffness, flexibility, relaxation, and intravaginal pressure, measured by any clinical examination method or tool.
Results
Twenty-one studies met the inclusion criteria. Seven PFM tone parameters were measured. Meta-analyses were conducted for myoelectrical activity, resistance, and anterior-posterior diameter of the levator hiatus. Myoelectrical activity and resistance were higher in women with PNCPP than in women without (SMD = 1.32 [95% CI, 0.36-2.29] and SMD = 2.05 [95% CI, 1.03-3.06], respectively). Women with PNCPP also had a smaller anterior-posterior diameter of the levator hiatus as compared with women without (SMD = −0.34 [95% CI, −0.51 to −0.16]). Meta-analyses were not performed for the remaining PFM tone parameters due to an insufficient number of studies; however, results of these studies suggested greater PFM stiffness and reduced PFM flexibility in women with PNCPP than in women without.
Clinical Implications
Available evidence suggests that women with PNCPP have increased PFM tone, which could be targeted by treatments.
Strengths and Limitations
A comprehensive search strategy was used with no restriction on language or date to review studies evaluating PFM tone parameters between women with and without PNCPP. However, meta-analyses were not undertaken for all parameters because few included studies measured the same PFM tone properties. There was variability in the methods used to assess PFM tone, all of which have some limitations.
Conclusion
Women with PNCPP have higher PFM tone than women without PNCPP; therefore, future research is required to understand the strength of the relationship between pelvic pain and PFM tone and to investigate the effect of treatment modalities to reduce PFM tone on pelvic pain in this population.