Active and Passive Components of Pelvic Floor Muscle Tone in Women with Provoked Vestibulodynia: A Perspective Based on a Review of the Literature

Aim. Pelvic floor muscle (PFM) dysfunctions, especially elevated tone or tension, are suggested to play an important role in the pathophysiology of provoked vestibulodynia (PVD). However, the involvement of the PFMs remains misunderstood as the assessment of muscle tone is complex and requires a thorough understanding of muscle physiology in relation to the characteristics and limitations of current PFM assessment tools. The aim of this review was to describe the structures and mechanisms involved in muscle tone in normally innervated muscle, and to discuss and relate these concepts to the PFM findings in women with PVD. Methods. A narrative overview of the literature retrieved from searches of electronic databases and hand searches. Results. Muscle tone in a normally innervated muscle comprises both active (contractile) and passive (viscoelastic) components. Current methods for evaluating PFM tone such as digital palpation, ultrasound imaging, pressure perineometry, dynamometry, and electromyography may evaluate different components. Research findings suggestive of PFM hypertonicity in women with PVD include elevated general PFM tone, changes in viscoelastic properties, and at least in some women, abnormal increases in electrogenic activity. Conclusion. There is a growing body of evidence to support the involvement of PFM hypertonicity in the pathophysiology of PVD. Limitations of the instruments as well as their properties should be considered when evaluating PFM tone in order to obtain better insight into which component of PFM tone is assessed. Future research is required for further investigating the underlying mechanisms of PFM hypertonicity, and studying the specific effects of physiotherapeutic interventions on PFM tone in women with PVD.