Urinary incontinence is described as the involuntary leakage of urine. It can be dived into several main types depending on the cause. It is vital, to understand the normal control of urine in order to manage urinary incontinence appropriately.

Micturition cycle

Overview

Micturition is the process of urine storage and voiding.

Controlled via interactions between:
1) Bladder (detrusor muscle).
2) Urethral sphincters.
3) Nervous system (autonomic and somatic).

There are two phases; the storage phase and the voiding phase:
A) Storage phase.
B) Voiding phase.[1]

Anatomy

• Bladder (Detrusor muscle): Smooth muscle that relaxes to store urine and contracts to void.
• Internal urethral sphincter: Smooth muscle (involuntary) at the bladder neck; maintains continence during filling.
• External urethral sphincter: Skeletal muscle (voluntary), controlled by the pudendal nerve, provides conscious control over urination.
• Pontine micturition centre (PMC): Brainstem area that coordinates the switch between storage and voiding.
• Higher cortical centres: Exert conscious control (allowing social continence). [1]

Physiology (storage phase)

Sympathetic nervous system (via hypogastric nerve, T11–L2):

• β3 receptors → relax detrusor muscle (allow bladder filling)
• α1 receptors → contract internal sphincter (prevent leakage)

Somatic nervous system (via pudendal nerve, S2–S4):

• Contracts external urethral sphincter for voluntary continence

Parasympathetic activity is inhibited during this phase.

Voiding phase physiology – Coordinated contraction of detrusor + relaxation of sphincters > micturition

Physiology (voiding phase)

When bladder volume reaches ~300–400 mL, stretch receptors in the bladder wall send signals via pelvic nerves (S2–S4) to the spinal cord and brain.

The pontine micturition centre (PMC) activates:

• Parasympathetic efferents (pelvic nerve, S2–S4):
• Acetylcholine acts on M3 receptors in the detrusor muscle → contraction
• > Inhibition of sympathetic (hypogastric) and somatic (pudendal) outflow → relaxation of internal and external sphincters
• Urine is expelled through the urethra as detrusor pressure rises and outlet resistance falls. [1]

Micturition cycle – Image from https://www.news-medical.net/health/Micturition-Reflex-Neural-Control-of-Urination.aspx

Types of incontinence

Stress incontinence: weakness of sphincter or pelvic floor despite normal detrusor control.

Urge incontinence: excessive detrusor contractions due to overactive parasympathetic stimulation.

Mixed: Both stress and urge.

Overflow incontinence: Failure of detrusor contraction or outlet obstruction.

Neurogenic bladder: Loss of coordination between detrusor and sphincter due to spinal or neurological disease. [2]

Presentation

Stress – Coughing or sneezing (raised intra-abdominal pressure) leads to incontinence.

Urge – Sudden need to urinate, uncontrollable. Often cant make it to the toilet in time.

Mixed – Comibbination of both.

Overflow – Inability to empty the bladder with resulting overflow of urine. [1,2]

Investigations

Urinalysis – Rule out infective or malignant causes.

Bloods tests – Assess kidney function. PSA if concerns with prostate.

Bladder diary – Monitor volume and type intake and record volume and frequency of micturition.

Flow studies – In males to assess flow rate and post void residual (i.e. If concerned about large prostate and overflow incontinence).

Urodynamics – Selected cases. Gives objective measurements of the the bladder storage and voiding phases. [2,3]

Management

Stress incontinence – Approach is to strengthen pelvic floor. First line treatment is pelvic floor exercises. Operative treatments include, peri-urethral injections, sling procedures, colposuspension, artificial urinary sphincters, diversion of urine into a conduit.

Urge incontinence – Approach is to reduce urgency and improve control. First line is bladder training, caffeine reduction and pelvic floor exercise. Medications to inhibit bladder contractions are helpful e.g. anticholinergics or beta 3 agonists. Operative options include, botox injections into bladder wall, sacral neuromodulation, augmentation cystoplasty, diversion of urine into a conduit.

Mixed – Both.

Overflow – If due to BPH can consider TURP procedure. Otherwise, intermittenet self catheterisation or indwelling cathteter (urethral or SPC). [2]

References

Written by Jacqueline Lee (FY2)
Edited by Joseph Latham (CT3)