Correspondence Scott Department of Urology, Baylor College of Medicine, 6560 Fannin Street, #2100, Houston, TX 77030, USA

Email tboone@bcm.tmc.edu

Original article

Weiss JP et al. (2007) Age related pathogenesis of nocturia in patients with overactive bladder. J Urol 178: 548–551   PubMed

Synopsis

Background

The prevalence of nocturia—waking one or more times during the night to void—increases with age. Nocturia can be caused by increased nocturnal urine output (nocturnal polyuria) or reduced nocturnal bladder capacity, both of which are influenced by age. The pathogenesis of nocturia has implications for treatment.

Objective

The objective of this study was to use indices to determine the cause of age-related nocturia in patients with overactive bladder (OAB) and nocturia.

Design and intervention

In this post hoc analysis, data were obtained from patients with OAB and nocturia who had completed a double-blind, placebo-controlled, randomized trial of the antimuscarinic agent tolterodine (extended release formulation). Patients were stratified according to age (<50 years, 50–70 years and >70 years) and sex. Exclusion criteria were stress incontinence, polyuria, or a postvoid residual urine volume >200 ml. A 7-day bladder diary was completed at baseline, in which patients recorded the time of each micturition during the day or night, and also their sleep cycles. For 2 days during this 7-day period, patients also used a standardized graduated measuring receptacle to record the volume of urine voided per micturition. The number of nightly voids and the nocturnal voided volumes were used to calculate the nocturia index, the nocturnal polyuria index, and the nocturnal bladder capacity index. The nocturia index was defined as the nocturnal voided volume divided by the maximum voided volume; a nocturia index >1 indicates that nocturia is due to nocturnal polyuria rather than a low nocturnal bladder capacity. The nocturnal polyuria index was defined as nocturnal voided volume divided by the volume per 24 hours; a nocturnal polyuria index >35% indicates that the diagnosis is nocturnal polyuria. The nocturnal bladder capacity index was defined as the actual number of nightly voids minus the nocturia index minus 1; a nocturnal bladder capacity index >0 indicates that the nocturnal bladder capacity is less than the maximum voided volume.

Outcome measures

The outcome measures were the nocturia index, the nocturnal polyuria index, and the nocturnal bladder capacity index.

Results

The study included 845 patients (49% men and 51% women). No sex-related or age-related differences in nocturia were observed in the study population at baseline. The mean number of nocturia episodes per night was 3.30 and 3.31 among men and women, respectively. The nocturia index increased significantly with increasing age (P = 0.0064), and the mean nocturia index was significantly different between men and women (2.63 and 2.42, respectively, P <0.0001). The nocturnal polyuria index also significantly increased with age (P = 0.0001), but there were no differences in the polyuria index between sexes (P = 0.6325). The nocturnal bladder capacity decreased significantly with age in both men and women (P = 0.0148).

Conclusions

In patients aged >70 years, nocturia is likely a result of nocturnal polyuria, whereas in patients aged <50 years, nocturia is likely a result of reduced bladder capacity.

Commentary

The 2002 International Continence Society defines nocturia as awakening at night one or more times to void. Nocturnal voiding should be preceded and succeeded by sleep.¹ Nocturnal polyuria is the major cause of nocturia in about 70% of patients;² diurnal polyuria and reduced bladder capacity represent the other urologic factors of symptomatic nocturia.

The age-related loss of restorative sleep, aggravated by nocturia, has a substantial effect on quality of life.³ For some patients, returning to sleep is not difficult; however, they would still qualify for many clinical trials that investigate nocturia. Most physicians consider two or more nocturnal voids enough to warrant investigation. The term 'fragmented sleep' has been used to describe the sleep disturbance associated with nocturia; however, when discussing nocturia with patients, the term fragmented sleep seems to be easier for patients to understand, in the same way that the term OAB is easier to understand than detrusor instability.

In addition to sleep impairment, the elderly are at increased risk of falls and fractures when getting up during the night to void. Two or more nocturnal voids have been associated with a twofold increase in falls among elderly patients when compared with patients with fewer voids.⁴ If the cognitive loss and reduced mobility experienced by the elderly are combined with symptomatic nocturia, the overall morbidity is substantial and requires medical therapy whenever possible.

This study by Weiss et al., which used post hoc data from a randomized, double-blind, placebo-controlled trial of tolterodine extended release, assessed age-stratified and sex-stratified patients with OAB and nocturia (a mean of 2.5 or more nocturnal voids per night). The authors concluded that OAB with nocturia in the younger patients was attributable to reduced nocturnal bladder capacity, whereas OAB with nocturia in the older patients was attributable to increased nocturnal urine output.

The authors promoted the use of validated diagnostic criteria using 24 h voiding diaries and urine volumes to calculate the nocturia index, the nocturnal polyuria index, and the nocturnal bladder capacity index. These indices rely upon accurate 7-day voiding diaries and measured urine volumes, but getting patients to fill out the diary and measure voided urine volumes for two 24h periods accurately is a real challenge. In my experience, this data gathering becomes even more difficult in elderly patients. Despite these difficulties, Weiss et al. show us for the first time how nocturnal urine production is affected by age and how nocturnal bladder capacity is a factor to consider in younger patients with symptomatic nocturia. The use of indices might help to determine the etiology of nocturia, and these noninvasive measurements could be used to select appropriate treatment for symptomatic nocturia. Weiss et al. emphasized that individualized treatment, based on a thorough understanding of the underlying etiology of the patient's nocturia, is important. Future targeted studies in an elderly population by additional investigators will determine if these indices prove useful in everyday practice.

Acknowledgments

The synopsis was written by Rachel Murphy, Associate Editor, Nature Clinical Practice.

References

1. van Kerrebroeck P et al. (2002) The standardisation of terminology in nocturia: report from the Standardisation Sub-committee of the International Continence Society. Neurourol Urodyn 21: 179–183 | Article | PubMed | ISI |
2. Rembratt A et al. (2002) What is nocturnal polyuria. BJU Int 90 (Suppl 3): 18–20 | Article |
3. Schneider T and Stanley N (2007) Impact of nocturia on sleep and energy. Eur Urol (Suppl 6): 585–593
4. Stewart RB et al. (1992) Nocturia: a risk factor for falls in the elderly. J Am Geriatr Soc 40: 1217–1220 | PubMed | ChemPort |

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Subject areas under which this article appears: Urinary incontinence, urodynamics and lower urinary tract dysfunction