Table of Contents
Page created on June 3, 2021. Last updated on June 6, 2022 at 09:18
Innervation of the bladder
There are three centres of bladder control in the CNS:
- Frontal cortex – which inhibits the PMC
- Pontine micturition centre (PMC)
- Onuf-nucleus in sacral spine
The muscles involved in urination are innervated like this:
- Parasympathetic fibres from sacral spine innervate:
- Detrusor muscle, causing contraction
- Sympathetic fibres from lower thoracic level innervate:
- Detrusor muscle, causing relaxation
- Internal sphincter, causing contraction
- Somatic (pudendal nerve) fibres from sacral spine innervate:
- External sphincter, causing contraction
Types of disturbance according to neuroanatomical location
We can distinguish three types of urinary bladder innervation disturbances based on the location of the lesion.
A suprapontine lesion, usually of the frontal lobe, causes loss of voluntary control of the urination. This can occur due to stroke, dementia, etc.
A spinal cord lesion between the pons and the Onuf nucleus causes detrusor-sphincter dyssynergy or detrusor hyperreflexia. This can occur due to multiple sclerosis, myelitis, etc. This is the most common site of lesion.
A subsacral lesion, below the Onuf nucleus, initially causes urinary retention, and later causes overflow incontinence. This can occur due to trauma or herniation, for example as part of cauda equina syndrome.
Types of disturbance according to pathomechanism
In detrusor-sphincter dyssynergy, the detrusor and sphincter muscles don’t contract in a coordinated way, causing the detrusor and sphincter to contract simultaneously, increasing the pressure in the bladder. It is usually seen in spinal cord lesion, and it usually causes urge incontinence.
Detrusor hyperreflexia or hyperactive bladder is usually seen in suprapontine or spinal cord lesion. It usually causes urge incontinence.
Detrusor areflexia or hypoactive bladder is usually seen in subsacral lesion. It usually causes overflow incontinence or residual urine.
Types of disturbance according to clinical features
Urge incontinence is characterised by urinary leak preceded by a strong urge to urinate. The patient usually can’t urinate properly despite the strong urge. It can be due to intravesicular (urological) problems or due to neurological problems. It usually occurs due to bladder hyperactivity or detrusor-sphincter dyssynergy.
Overflow incontinence is characterised by the bladder filling up, causing urine to dribble out. This can be due to a peripheral lesion causing hypoactivity of the bladder, or due to bladder obstruction.
Stress incontinence is characterised by urinary leak when the intraabdominal pressure increases, like when coughing. This is usually not neurological in origin, but rather urological or gynaecological.
Treatment
Urge incontinence:
- Anticholinergics
- TCAs with strong anticholinergic effect (imipramine)
- Alpha blockers
- Beta 3 agonists
- Patient self-catheterisation
Overflow incontinence:
- Patient self-catheterisation
Stress incontinence:
- TCAs with strong anticholinergic effect (imipramine)
- Duloxetine
- Surgery
In urge incontinence, why would treatment consist of anticholinergics but also alpha and beta blockers?
Would it not be contradictory to use a parasympatholytic and sympatholytic?
Fair point, but that’s reality, it doesn’t always make sense from a basic physiological standpoint. Both anticholinergics and alpha blockers are used. Not beta blockers though, removed that.
They are not contradictory;
– Alpha-blockers act on alpha-1-A receptors, leading to relaxation of the urethral sphincter
– Beta-3-agonists (not blockers!) act selectively on Beta-3 receptors and causes relaxation of the smooth muscle of the bladder
– M3 antagonists causes relaxation of the detrusor muscle