Purpose: Nocturia is caused by increased nocturnal urine output (nocturnal polyuria) and/or diminished nocturnal bladder capacity. We retrospectively evaluated the causes of nocturia in patients with overactive bladder and nocturia.
Materials and methods: A total of 850 patients (18 years or older) with symptoms of overactive bladder (8 or more micturitions per 24 hours and urgency or urgency urinary incontinence) and nocturia (mean of 2.5 or more episodes per night) were enrolled in a 12-week study of tolterodine ER (4 mg QD) vs placebo. Of this total 845 patients (417 men and 428 women) completed 7-day bladder diaries. Patients were stratified post hoc by sex and age groups (less than 50, 50 to 70, more than 70 years). Indices of nocturnal urine production (nocturia index, nocturnal polyuria index and nocturnal bladder capacity index) were compared using ANOVA (alpha level 0.05). Higher nocturia index and nocturnal polyuria index values suggest that nocturia occurs because of nocturnal urine overproduction. Higher nocturnal bladder capacity index values suggest that nocturia occurs because of decreased nocturnal bladder capacity.
Results: There were no statistically significant gender or age related differences in baseline nocturnal micturitions. Nocturia index increased significantly with age (p <0.0001), and values were significantly higher among men than women for all age groups (p = 0.0064). Nocturnal polyuria index increased significantly with age (p <0.0001) and there were no gender differences. For nocturnal bladder capacity index there was a significant decrease with advancing age among men (1.75 greater than 1.16 greater than 0.90) and women (1.53 greater than 1.42 greater than 1.08, P(interaction) = 0.0148).
Conclusions: In younger patients with overactive bladder, decreased nocturnal bladder capacity has a greater role in the pathogenesis of nocturia symptoms, whereas in older patients increased nocturnal urine output has a greater role.