The pathophysiology of stress urinary incontinence: a systematic review and meta-analysis

Abstract

Introduction and hypothesis: To evaluate the evidence for pathologies underlying stress urinary incontinence (SUI) in women.

Methods: For the data sources, a structured search of the peer-reviewed literature (English language; 1960-April 2020) was conducted using predefined key terms in PubMed and Embase. Google Scholar was also searched. Peer-reviewed manuscripts that reported on anatomical, physiological or functional differences between females with signs and/or symptoms consistent with SUI and a concurrently recruited control group of continent females without any substantive urogynecological symptoms. Of 4629 publications screened, 84 met the inclusion criteria and were retained, among which 24 were included in meta-analyses.

Results: Selection bias was moderate to high; < 25% of studies controlled for major confounding variables for SUI (e.g., age, BMI and parity). There was a lack of standardization of methods among studies, and several measurement issues were identified. Results were synthesized qualitatively, and, where possible, random-effects meta-analyses were conducted. Deficits in urethral and bladder neck structure and support, neuromuscular and mechanical function of the striated urethral sphincter (SUS) and levator ani muscles all appear to be associated with SUI. Meta-analyses showed that observed bladder neck dilation and lower functional urethral length, bladder neck support and maximum urethral closure pressures are strong characteristic signs of SUI.

Conclusion: The pathology of SUI is multifactorial, with strong evidence pointing to bladder neck and urethral incompetence. While there is also evidence of impaired urethral support and levator ani function, standardized approaches to measurement are needed to generate higher levels of evidence.

Keywords: Dynamometry; Electromyography; Females; Magnetic resonance imaging; Stress urinary incontinence; Ultrasound.

Fig. 1

Flow chart of the search strategy and selection of studies

Fig. 2

Standardized mean differences (SMD) in the maximal urethral pressure (MUP) and maximal urethral closure pressure (MUCP) in stress-incontinent women compared with continent women. For studies by Hilton (1983) and Henriksson et al. (1979b), average values across SUI severity and age groups were used respectively. For the study by Meyer et al. (1996a) an average of SUI groups with and without a low pressure urethra (failure to generate MUCP > 20 cmH₂O) in supine position was used. For the study by Hale et al. (1999) the MUCP at rest was used. For the study by Kuhn et al. (2008) estimates were made from the published figure (SUI group: 23 ± 13.5 cmH₂O; control group: 55 ± 20 cmH₂O)

Fig. 3

Mean difference (MD) in functional urethral length in stress-incontinent women compared with continent women. For the study by Li et al. (2020), the perimenopausal control group was used in this analysis

Fig. 4

Risk ratio for bladder neck funneling in stress-incontinent women compared with continent women. For the study by Hoffmann and Ulrich (1966), the SUI group without pelvic organ prolapse was used in this analysis

Fig. 5

Standardized mean differences (SMD) of beta angles measured at rest in stress-incontinent women compared with continent women