Does transition of urinary incontinence from one subtype to another represent progression of the disease?

Introduction and hypothesis Mixed urinary incontinence (UI) is, on average, more severe than urgency UI or stress UI. We tested the hypothesis that mixed UI is a more advanced stage of UI by comparing transition probabilities among women with stress, urgency, and mixed UI. Methods We used data from the General Longitudinal Overactive Bladder Evaluation Study-UI, which included community-dwelling women, aged 40+ years, with UI at baseline. Study participants completed two or more consecutive bladder health surveys every 6 months for up to 4 years. Using sequential 6-month surveys, transition probabilities among UI subtypes were estimated using the Cox-proportional hazards model, with the expectation that probabilities from stress or urgency UI to mixed UI would be substantially greater than probabilities in the reverse direction. Results Among 6,993 women 40+ years of age at baseline, the number (prevalence) of women with stress, urgency, and mixed UI was 481 (6.9%), 557 (8.0%), and 1488 (21.3%) respectively. Over a 4-year period, the transition probabilities from stress UI (34%) and urgency UI (27%) to mixed UI was significantly higher than probabilities from mixed to stress UI (6%) or to urgency UI (rate = 9%). The adjusted transition hazard ratio for stress UI and urgency UI was 2.06 (95% CI: 1.73-2.92) and 1.85 (95% CI: 1.63-2.57) respectively compared with mixed UI. Conclusion The substantially higher transition from stress UI and urgency UI to mixed UI supports the hypothesis that mixed UI might represent a more advanced stage of UI that may have implications for understanding disease progression.