Nocturia

Nocturia can be defined as the need to wake and pass urine at night (in contrast to Nocturnal Enuresis in Children, where urine is passed unintentionally during sleep). One episode of nocturia per night is considered within normal limits.

Most people can identify the number of times they wake to pass urine, and this is usually denoted as, for example, "nocturia x 3", meaning waking to pass urine three times per night.

The term nocturia as a symptom, is generally used to mean that the patient is waking to pass urine more frequently than normal, i.e. more than once per night. The rest of this article will use nocturia in this way.

Nocturia is a common symptom in both men and women.³ It can be troublesome in itself, by disturbing sleep, and can have a significant impact on quality of sleep and quality of life.

Nocturia is a symptom, not a diagnosis. It is important to assess underlying causes, as some important conditions, such as diabetes, may present in this way.

There are 3 ways in which nocturia can be caused: by problems of fluid balance; by neurological diseases affecting bladder control; or by disorders of the lower urinary tract. It is easy to overlook the first two categories while concentrating on the urinary tract.

Fluid balance causes of nocturia²

Polyuria (day and night) - defined as urine volume >40ml/kg/24 hours

• Excess fluid intake - including alcohol⁴
• Diabetes mellitus
• Diabetes insipidus - including iatrogenic, e.g. lithium⁵
• Hypercalcaemia⁶
• Renal failure (more likely in chronic renal failure rather than acute)^7,8

• Excessive evening fluid intake, including alcohol⁴
• Diuretics (may depend on time of day taken)
• Disruption of normal vasopressin (ADH) secretion - often due to age⁹
• Nocturnal redistribution of fluid - cardiac failure; other causes of oedema, e.g. venous stasis
• Sleep apnoea (unknown mechanism)¹⁰

Neurological causes of nocturia

The bladder is controlled via the brain, spinal cord tracts, sacral segments S2-4 and peripheral nerves. Therefore, many neurological conditions affect bladder function. Nocturia may be a symptom because:

• The neurological problem may cause urinary frequency: this can occur in multiple sclerosis,¹¹ and has been reported as an early feature of cervical cord compression¹² and tethered spinal cord syndrome.¹³
• The neurology may cause retention of urine, which either results in frequency and true nocturia, or leads to overflow incontinence, which may be misinterpreted as nocturia.

Doctors should be aware that:

• If retention occurs in women or patients under 60, who are unlikely to have bladder obstruction, consider neurological causes.¹⁴
• Important, urgent conditions to diagnose are:
  • Cord compression¹⁵ and cauda equina syndrome. The bladder innervation is easily damaged, and prompt referral/treatment can save bladder function.¹⁵
  • Tethered spinal cord syndrome (see below), though usually less acute, again needs early referral.¹³

Other common neurological disorders causing urinary symptoms are:

• Multiple sclerosis¹¹
• Parkinson's disease¹⁶
• Diabetic cystopathy¹⁷
• Tethered spinal cord syndrome (as above): this is probably under-recognised.¹³ It has also been reported that spina bifida occulta is associated with lower urinary tract dysfunction, which may relate to tension on spinal cord or nerves.¹⁸

Lower urinary tract causes of nocturia^2,19

This is a 'low nocturnal bladder capacity', and can be classified as due to:

• Bladder outflow obstruction (where chronic retention in effect lowers any additional bladder capacity)
  • Prostatic disease
  • Urethral disease - this occurs in both men and women²⁰
• Bladder overactivity
• Sensory urgency
• Urinary tract infection
• Inflammation, e.g. interstitial cystitis
• Malignancy
• Pregnancy

Nocturia in often ascribed to prostatic disease (in men), without due consideration of other causes.^3,9 Other factors, or a combination, are just as likely to be the cause. The cause of nocturia can usually be determined by simple assessment using history, examination and a voiding diary, plus urodynamics if necessary.⁹

History

• Clarify the patient's symptoms, and ask about other lower urinary tract symptoms (see box for details).
• How are these symptoms affecting life and sleep?
• Could this be a fluid balance problem?
  • Fluid intake pattern (including alcohol).
  • Excessive thirst suggests diabetes (mellitus or insipidus) or hypercalcaemia.
  • Are there any systemic illnesses which could be contributing, e.g. cardiac failure, obstructive sleep apnoea, oedema, chronic renal failure?
• Are there any neurological or spinal symptoms: neck or back pain; limb weakness or sensory loss? Important symptoms and signs are:
  • Abnormal gait or spasticity suggest upper motor neurone lesions
  • Limb sensory loss or weakness: widespread or bilateral symptoms are worrying and suggestive of cord or cauda equina lesions (nerve root lesions usually cause more localised and unilateral symptoms).
  • Constipation can also occur as part of sphincter disturbance.
  • Saddle area sensory loss and sexual dysfunction ('numb bum') suggest cauda equina syndrome.
• Medication: any contributing medicines, e.g. diuretics, excessive calcium supplementation or antacids,⁶ lithium?

Examination

• Percuss abdomen for enlarged bladder
• Leg oedema present?
• Urine dipstick will screen for, but not exclude, diabetes mellitus, infection, haematuria and proteinuria
• Other relevant examination, depending on suspected cause:
  • cardiovascular
  • neurological - especially important if there is urinary retention where obstructive causes are unlikely, i.e. in women and the under-60s
  • rectal examination (men) to assess prostate; pelvic examination (women)

Investigations in primary care¹

• Voiding diary by the patient: an example is given below.
• Blood tests: renal function, electrolytes, glucose and calcium.
• Midstream urine culture and microscopy.
• Urodynamics: GPs may have direct access to these clinics, which assess urinary flow rate and residual volume. Some clinics perform additional measurements, such as bladder capacity by ultrasound, bladder pressures using a urethral catheter, or fluoroscopic pressure and flow measurement.

Urgent problems which will need same day referral are:

• Metabolic problems, e.g. diabetes mellitus if ketotic, dehydrated or severe hyperglycaemia; hypercalcaemia; significant renal failure, electrolyte disturbance or lithium toxicity
• Neurological problems: suspected cord compression or cauda equina syndrome
• Urological problems: acute retention, chronic retention with renal impairment

Other problems, after initial assessment and investigations, can be classified according to the type of cause above, and then managed accordingly. Note that several conditions may coexist, all contributing to nocturia, e.g. cardiac impairment, diabetes mellitus and prostatic hypertrophy.