What causes nocturia?

Causes of Nocturia

Nocturia is primarily caused by medical conditions affecting the "SCREeN" areas: Sleep disorders, Cardiovascular conditions, Renal disease, Endocrine disorders, and Neurological conditions, as well as medication effects and xerostomia. 1

Primary Pathophysiological Mechanisms

Nocturia occurs through three main mechanisms:

1. Increased urine production at night (nocturnal polyuria)

   • Defined as >33% of 24-hour urine volume produced during nighttime 2
   • Accounts for up to 80% of nocturia cases in men with BPH 3

2. Decreased bladder storage capacity

   • Due to overactive bladder, BPH, or other urological conditions
   • Results in inability to store normal urine volumes overnight

3. Global polyuria

   • Defined as >2.5L urine production per 24 hours 1
   • Leads to increased voiding frequency both day and night

4. Sleep disorders

   • Increased arousals lead to awareness of bladder filling 1

Specific Medical Causes by Category

Sleep Disorders

• Obstructive sleep apnea (OSA)
• Insomnia
• Restless legs syndrome (RLS)
• Periodic limb movements of sleep (PLMS)
• Parasomnias 1

Cardiovascular Conditions

• Congestive heart failure (CHF)
  • Causes daytime fluid retention and nighttime diuresis
• Hypertension
• Peripheral edema 1

Renal Conditions

• Chronic kidney disease (CKD)
  • Impairs urine concentrating ability in renal medulla 1

Endocrine Disorders

• Diabetes mellitus
  • Causes osmotic diuresis from glycosuria 1
• Diabetes insipidus
  • Results from insufficient antidiuretic hormone (ADH)
• Overactive or underactive thyroid
• Menopause/hormonal changes 1

Neurological Conditions

• Parkinson's disease
• Multiple sclerosis
• Spinal cord injuries
• Autonomic dysfunction
  • Orthostatic hypotension (fall of 20 systolic or 10 diastolic within 3 minutes of standing) 1

Medication-Related Causes

• Diuretics (especially when taken in evening)
• Calcium channel blockers
• Lithium
• NSAIDs
• Medications causing xerostomia (dry mouth):
  • Anxiolytics
  • Antidepressants
  • Antimuscarinics
  • Antihistamines
  • Decongestants
  • Antiparkinsonian drugs
  • Antipsychotics 1, 2

Urological Causes

• Benign prostatic hyperplasia (BPH)
  • Causes decreased functional bladder capacity 3
• Overactive bladder syndrome
• Bladder outlet obstruction
• Incomplete bladder emptying with high post-void residual 4

Diagnostic Algorithm

1. Obtain a 72-hour bladder diary documenting:

   • Timing and volume of voids
   • Fluid intake patterns
   • Timing of sleep 1, 2

2. Screen for SCREeN conditions with targeted questions:

   • "Do you have problems sleeping aside from needing to urinate?"
   • "Have you been told you gasp or stop breathing at night?"
   • "Do you experience ankle swelling?"
   • "Do you get short of breath walking certain distances?"
   • "Have you been feeling excessively thirsty?" 1

3. Perform baseline investigations:

   • Urinalysis (for glucose, protein, blood)
   • Blood tests: electrolytes/renal function, thyroid function, calcium, HbA1c
   • Blood pressure assessment 1

4. Calculate nocturnal polyuria index:

   • Nocturnal urine volume ÷ 24-hour urine volume

   • 33% indicates nocturnal polyuria 2, 4

Clinical Pearls and Pitfalls

• Pitfall: Assuming nocturia is always due to urological causes. In reality, up to 80% of cases involve nocturnal polyuria from non-urological causes 3.

• Pitfall: Failing to adjust timing of medications. Simply changing diuretic administration from evening to morning can significantly reduce nocturia 2.

• Pitfall: Missing sleep disorders. Patients with OSA may not report classic symptoms but still have nocturia as a manifestation 1.

• Pearl: Nocturia is often multifactorial - 36% of patients have both nocturnal polyuria and nocturnal detrusor overactivity 4.

• Pearl: For elderly patients, safety considerations are paramount - installing nightlights and ensuring clear pathways to the bathroom can prevent falls 2.

By systematically evaluating these potential causes through careful history, physical examination, and targeted testing, the underlying etiology of nocturia can be identified and appropriately managed.