Underactive bladder syndrome

First of all, we should get some of the medical jargon explained. “Cauda equina” relates to the nerves in the spine which travel independently to the spinal cord. The spinal cord is one solid structure, with billions of individual nerve fibres making up the structure. The spinal cord has different zones which carry information relating to light touch, sharp touch, vibration, joint position sense, movement and temperature recognition. The spinal cord also carries messages from the front of the brain which tell the bladder not to contract, as it’s not yet convenient to empty the bladder (eg someone’s gone and finished the toilet roll in the bathroom and you need to get a new roll from the cupboard).

The spinal cord sends out a pair of nerves at each different block of spine, or vertebra, which supply all the attributes described above, but they are now in each individual nerve root, AKA spinal nerve. The nomenclature isn’t ideal for spinal nerves, because someone in their wisdom decided to number the bones of the spine differently to the nerves of the spine, giving the neck eight pairs of numbered nerves compared with seven neck bones (cervical spine vertebrae). This means that in the neck, the named nerve for each bone is above its respective vertebra/spine, but everywhere else in the spine, the named nerves are below their respective vertebrae/ spinal levels.

Moving on to the nerves below the spinal cord- the cord peters out at the level of the upper lumbar spine and becomes a collection of individual spinal nerves travelling together in the spinal canal. Each individual nerve now has its full complement  of attributes, instead of the organised structure of the single spinal cord. This collection of central spinal nerves are called the cauda equina and they supply the legs, bladder and bowel functions.

All the nerves which supply movement within the cauda equina nerve group and the spinal nerves can also be called lower motor neurones. They communicate with the movement nerves in the spinal cord and brain called upper motor neurones.

Without getting bogged down in too much detail, when something goes wrong with the spine, it can either affect the spinal cord (including its upper motor neurones) or it can effect the cauda equina (including its lower motor neurones).

If the nerves are severely damaged and stop the electricity supply to the muscles, the muscles become paralysed, ie they can’t move when you try to move them. The type of paralysis can be either flaccid (floppy limbs that won’t move) or spastic (high-tone, stiff limbs that won’t move). Flaccid paralysis is due to cauda equina damage and spastic paralysis is due to spinal cord damage.

Bladder function is affected with both upper and lower motor neurone injuries. Lower motor neurone injuries include cauda equina syndrome ie damage to the cauda equina nerves which include the lower motor neurones. The result is a condition called neurogenic bladder. Neurogenic bladder as a term covers a multitude of symptoms and isn’t particularly helpful as a diagnosis in itself. For cauda equina syndrome, the bladder problem associated with this may be more appropriately called “detrusor underactivity”, or DU. The detrusor muscle is what wraps around the bladder and makes it into one muscular bag. Urine feeds into the bladder from the kidneys and urine leaves the bladder when the sphincter/valves keeping the urine inside (internal and external urethral sphincters) are voluntarily relaxed.

Detrusor underactivity can behave very similarly to bladder outflow obstruction- a really common condition in men with enlarged prostate glands. The basic difference between the inability to wee due to an obstruction and the inability to wee because the bladder won’t contract is the symptom of pain. Painful retention is typical of prostate problems, but painless retention implies that the nerves to the bladder aren’t sensing the overstretching of the bladder wall as the kidneys keep feeding urine into the bladder, but the sphincters won’t relax to let the urine out and the detrusor muscle isn’t able to contract properly either.

In detrusor underactivity, the process of weeing is slow, sometimes requiring physical pressure against the lower abdomen to try and squeeze urine out of the bladder. The urine flow is a trickle and the bladder does not completely empty itself. Sometimes, the sphincters are not very tight and as the bladder over-fills, the pressure inside the bladder becomes greater than the closing pressure of the sphincters, with the result being overflow incontinence. Sometimes, the sphincters never allow urine to pass through and the bladder needs to be manually drained using a temporary or permanent catheter.

Diagnosis of Underactive Bladder

An ultrasound machine is risk-free and non-invasive. It can measure the volume of urine held inside the bladder. Using the ultrasound, we can measure the pre-voiding bladder volume and the post-voiding residual bladder volume (pre- and post-void bladder volumes). A pre-voiding volume of 400mls and upwards should usually coincide with the urge to pass urine, so volumes approaching a litre are definitely not normal. Post-voiding volumes should ideally be zero, ie the bladder completely empties. A residual volume of under 100mls is acceptable, but residuals of 400mls and upwards indicate that manual drainage of the bladder is needed, to prevent the bladder from over-distending and weakening the detrusor muscle further as a result.

Urodynamics are a series of specialised tests performed by a urology team and include measuring urine flow rates and pressure measurements of the bladder and sphincters.

Treatment options for Underactive Bladder

The targets for treatment include helping the detrusor muscle to contract more effectively or interventions which relax the sphincters to allow urine to leave the bladder more easily (you can see how this can be problematic if this strategy is too effective).

1 The 350mls rule

The detrusor muscle is at its strongest when the bladder is filled with roughly 350mls of fluid ie the volume of a typical can of soda. If the person with cauda equina syndrome can be taught to try and empty the bladder frequently, when around 350mls are passed, then the detrusor is at its optimal function.

2 ISC- intermittent self-catheterisation

This is the mainstay management of cauda equina syndrome bladder problems, which involves manually draining the bladder at regular intervals to avoid over-distending the bladder. This method avoids medications or surgery, but involves training to get the technique as hygienic as possible, plus it involves having a regular supply of catheters. This technique tends to be less hassle to perform in men compared with women, who have shorter urethras.

3 Medication

Muscarinic agonists and cholinesterase inhibitors are the two classes of medication used to treat underactive detrusor problems. Examples include bethanechol and distigmine, with mixed reports of response in the published literature (some outcomes are very positive, whereas others are disappointing).

 4 Electrical stimulation

This is an uncommon treatment used when the detrusor can still work, but not very effectively. Intravesical stimulation and Sacral nerve stimulationare both examples of available techniques.

Future Direction

Stem cell therapy is not yet in the clinical arena, but laboratory testing is ongoing, so watch this space.

Further Reading

Here is a useful, if slightly scientific, overview of underactive bladder, , and another one here which give a comprehensive account of the underactive bladder, which has many causes, including cauda equina syndrome.

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