Urodynamically defined stress urinary incontinence and bladder outlet obstruction coexist in women

The definition and significance of female bladder outlet obstruction (BOO) are poorly understood. We identified patients with urodynamic evidence of BOO in a cohort of women with stress urinary incontinence (SUI).

Women with SUI were identified from a videourodynamic data base and pressure flow studies were reexamined. Subjects were excluded if detrusor pressures could not be measured. BOO was diagnosed if the maximum flow rate was less than 12 ml per second and detrusor pressure at maximum flow was greater than 20 cm water or maximum detrusor pressure was greater than 20 cm water in those without measurable flow. Clinical and urodynamic characteristics were compared in the obstructed and unobstructed groups.

Of 104 eligible subjects 19 (18.3%) had BOO. Maximum flow rate, mean flow rate and voided volume were significantly less in the BOO group than in the unobstructed group (8.7 vs 13.5 ml per second, p = 0.004, 5.9 vs 7.9 ml per second, p = 0.001 and 180 vs 272 ml, p = 0.008). Detrusor pressure at maximum flow, maximum detrusor pressure and post-void residual volume were significantly greater in the BOO group than in the unobstructed group (28 vs 15 cm water, p <0.0001, 31 vs 19 cm water, p <0.0001 and 71 vs 10 ml, p = 0.008). Etiologies of BOO identified in the 19 subjects included prior anti-incontinence or prolapse surgery in 6, neurological conditions in 4, cystocele in 2, dysfunctional voiding in 3 and idiopathic in 5.

SUI and BOO can coexist even in the absence of common causes of obstruction.