SUFU 2018: Pathophysiology of Nocturia

Austin, TX ( Jeffrey P. Weiss, MD gave a State of the Art lecture on the pathophysiology of nocturia.   He describes the most important step to the evaluation of nocturia is a 24 hour voiding diary. 

The first void of the morning is included in the nocturnal urine volume.  He describes how to obtain the nocturnal polyuria index (NPI).  If the nocturia voided volume divided by 24 is > 33%, it is consistent with nocturnal polyuria.  Nocturnal bladder capacity index is also able to be calculated.

Etiologies for Nocturnal Polyuria

Etiologies include:

  • congestive heart failure (CHF)
  • diabetes mellitus (DM)
  • obstructive sleep apnea (OSA)
  • peripheral edema
  • and excessive nighttime fluid intake
Diminished Bladder Capacity Causes

Diminished nocturnal bladder capacity can be caused by:

  • prostatic obstruction
  • nocturnal DO, neurogenic bladder, bladder, prostate, or urethral cancer
  • cystitis/infection.
Global Polyuria

Global polyuria is defined as a 24-hour urine output of greater than 40 cc/hour.  Etiologies include DM, diabetes insipidus, or polydipsia (behavioral or psychogenic). 

Pathophysiology Case Reports

Dr. Weiss then gave two case reports to demonstrate how to evaluate two separate men with nocturia.  He described how to use urine osmolarity to determine if the patient is concentrating their urine.  He advocates for ruling out obstructive sleep apnea with sleep studies (treat with CPAP), take diuretics in the mid-afternoon, drink only to thirst, and review medications to rule out causes of nocturia (SSRI’s, diuretics, calcium channel blockers). 

Elderly Patients

In elderly patients, nocturia is often the result of urine overproduction, while in the younger patient, it is often a result of a decreased bladder capacity.   There is a direct correlation between decreased bladder capacity and degree of nocturia.

Additional Info

In the course of his lecture on the pathophysiology of nocturia, he also presented helpful algorithms on the management for the different etiologies of nocturia.


Presented by: Jeffrey P. Weiss, MD

Written by: Cristina Palmer, DO. Female Urology, Pelvic Reconstruction, Voiding Dysfunction Fellow, Department of Urology, UC Irvine Medical Center, Orange, California at the Society of Urodynamics, Female Pelvic Medicine & Urogenital Reconstruction Winter Meeting (SUFU 2018), February 27-March 3, 2018, Austin, Texas

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