The natural history of urinary incontinence subtypes in the Nurses' Health Studies

Urinary incontinence subtypes often differ by symptom severity and treatment profiles; in particular, mixed urinary incontinence is generally associated with worse symptoms and less successful treatment. Yet, limited information exists on the natural history of different urinary incontinence subtypes, which could help to better identify and treat patients prior to development of more intractable disease.

To evaluate the onset of urinary incontinence subtypes, and transitions between subtypes over 8 years, using 2 large cohorts of middle-aged and older women with incident urinary incontinence.

We identified 10,349 women with incident urinary incontinence (stress, urgency, and mixed subtypes) from the Nurses' Health Study and the Nurses' Health Study II who were 41-83 years of age, using repeated mailed questionnaires. We defined stress urinary incontinence as leakage with coughing, sneezing, or activity; urgency urinary incontinence as urine loss with a sudden feeling of bladder fullness or when a toilet was inaccessible; and mixed urinary incontinence when women reported that stress and urgency symptoms occurred equally. In subsequent questionnaires 4 and 8 years later, we continued to track symptom severity and subtypes. In addition, to obtain predicted probabilities of urinary incontinence subtypes 4 years and 8 years after urinary incontinence onset, we used multivariable-adjusted generalized estimating equations with a multinomial outcome.

At urinary incontinence onset in 2004-2005, 56% of women reported stress urinary incontinence symptoms, 23% reported urgency urinary incontinence symptoms, and 21% reported mixed urinary incontinence symptoms. Women with stress urinary incontinence or urgency urinary incontinence at onset were likely to report the same urinary incontinence type 4 and 8 years later (stress urinary incontinence at onset: 70% and 60% reported stress urinary incontinence at years 4 and 8, respectively; urgency urinary incontinence at onset: 68% and 64% reported urgency urinary incontinence at years 4 and 8, respectively). Nonetheless, for both stress and urgency urinary incontinence, women with more severe symptoms at onset were more likely to progress to mixed urinary incontinence. Women with mixed urinary incontinence at onset had more variation over time, although the largest subset continued to report mixed urinary incontinence (45% reported mixed urinary incontinence at year 4; 43% reported mixed urinary incontinence at year 8). Few women across all urinary incontinence subtypes reported resolution of symptoms over 4-8 years of follow-up (4-12%). When considering the likelihood of remaining with or progressing to mixed urinary incontinence over follow-up, according to age, body mass index, and urinary incontinence severity, we found that older and younger women had similar predicted probability of remaining with or progressing to mixed urinary incontinence (eg, women <60 years of age at onset with severe mixed urinary incontinence had a 54% (95% confidence interval, 53-55) probability of mixed urinary incontinence 8 years later, vs 57% (95% confidence interval, 56-58) of women ≥70 years of age with severe mixed urinary incontinence at onset). Obese women were somewhat more likely to progress to mixed urinary incontinence regardless of urinary incontinence type at onset (eg, women with body mass index <25 kg/m² at onset with severe stress urinary incontinence had a 30% predicted probability of mixed urinary incontinence 8 years after onset, vs 36% of women with body mass index of 30+ kg/m² at onset with severe stress urinary incontinence).

Most women with incident stress and urgency urinary incontinence continued to experience similar subtype symptoms over 8 years. However, obese women and those with more severe symptoms were more likely to remain with or progress to mixed urinary incontinence.