An underactive bladder (UAB) is one that has lost its ability to fully contract and empty itself after voiding. The medical terms hypotonic and atonic bladder denote a bladder that has lost that contractility partially and fully respectively.
Causes of Underactive Bladder
A bladder that has been obstructed for many years can overstretch and become a ‘baggy’ pouch such that its muscle layer has also become stretched and weakened. Some causes of bladder obstruction include prostatic enlargement in men and urethral meatal stenosis (scarring of the opening of the tube draining the bladder), which can also occur in post-menopausal women.
Peripheral nerves coming from the lower spinal cord supply the bladder. They are responsible for transmitting bladder sensation to the brain and also coordinating bladder contraction during voiding. If these nerves are damaged, the bladder cannot sense and contract properly. Examples of such conditions are diabetes, multiple sclerosis, radiotherapy, pelvic surgery, or spinal cord injury (lower levels).
What are the symptoms?
Patients usually complain of difficulty passing urine at all phases of voiding. It is difficult to start a stream and often this would take many minutes. Patients need to sit and bear down, lean forward, strain or press on the lower abdomen to help empty the bladder. Urination happens in small dribbles and takes a long time to complete. Sometimes patients describe prolonged dribbling at the end with the need to double or triple void. There is often a sense of incomplete bladder emptying and patients would revisit the toilet soon after leaving it.
People with UAB can also have bladder storage symptoms including urinary frequency (need to void often), urgency, and nocturia (waking up multiple times at night to void). A bladder that does not empty properly will refill faster and therefore result in more frequent voiding. A delayed awareness of bladder filling until the last moment when urine is about to overflow into the urethra, may trigger a sense of urgency. Sometimes these storage bladder symptoms may also be due to chronic urinary infection which can occur in a bladder that does not empty well.
When the kidneys make urine and constantly fill a bladder that is unable to empty, it will overflow and cause incontinence. It is akin to a cup of water that keeps filling up from below, and ‘overflowing’ at the top. This type of leakage often occurs all throughout the day with the patient being unaware.
Loss of bladder awareness
When full, a normal bladder would send signals to the brain. If the bladder has also lost some function in the nerves carrying sensation, these signals are not sent. In these patients, they may have less urge to urinate and can go for prolonged hours before doing so.
What complications can arise from an underactive bladder?
The urine that gets left behind in the bladder can act as a source of urinary tract infection. This infection can be recurrent unless a way to drain the bladder is instituted.
Sediments can also accumulate in the urine and form bladder stones. These stones can harbour bacteria, promote infections, and cause symptoms like poor, interrupted urinary flow, urinary frequency and blood in the urine.
Chronic straining to void can result in other medical conditions such as haemorrhoids, hernias, and vaginal prolapses.
More uncommonly, the urine in the bladder can build up enough pressure such as to cause reflux up the ureters (tubes that join the kidneys to the bladder), and cause kidney damage.
What are the investigations?
A bladder diary is very useful in determining how much urine can be passed spontaneously and how frequently voiding occurs. If combined with intermittent self-catheterisation (see below) after a voluntary void, it can measure how much residual volume is left in the bladder. The ratio of spontaneously voided urine volume to the residual volume (voiding efficiency) gives an idea of how well the bladder can contract.
Urinary flow rate
Measurements of urinary flow rate and post-void bladder scan(uroflow study) often show a weak stream with a large volume of urine left in the bladder after a void. However, the causes of the weak stream cannot be differentiated (obstruction vs impaired bladder contractility) from a simple flow rate test itself. A urodynamics test is needed for that.
Radiological imaging studies
In some patients with no bladder symptoms, an ultrasound or CT study done for other reasons is often what incidentally showed the enlarged bladder. The bladder volume can sometimes be measured at more than 1L. Otherwise, an ultrasound of the urinary tract can be done to measure the prostate volume (in men) and look for kidney abnormalities.
Urodynamics (bladder function study)
Urodynamics is very useful in diagnosing the underactive bladder. Patients often have decreased bladder sensation, and impaired bladder contractility during voiding combined with a large residual volume left in the bladder after a void. Often, such patients need to use abdominal straining to help them void.
What are the treatments?
The aims of treatment are to ensure good bladder emptying, and thus prevent complications like infections, bladder stones, or kidney damage. Treatments range from simple observation to some form of catheterisation and the bladder pacemaker (sacral neuromodulation).
Intermittent self-catheterisation (ISC)
In those who still have good hand-eye coordination, intermittent self-catheterisation (ISC) can be taught. Here patients are taught to self-insert a small catheter into the bladder to drain it at regular intervals. Once the bladder is empty, the catheter is withdrawn. It usually takes 3 to 5 minutes when a patient becomes proficient.
Patients are also taught how to clean and store the catheters. A continence nurse can teach the techniques and also provide contacts for catheter supplies. Studies have shown that this is an effective way of managing the symptoms and also preventing complications. These patients are often told to keep a bladder diary to document their progress.
In those who are frail or have poor hand-eye functions, a permanent catheter is often the solution. This is less preferable to ISC but is sometimes necessary. Once inserted, the catheter needs to be changed every 4 to 6 weeks by a community nurse. The catheter is connected to a bag that is attached to the leg (leg bag) and can be hidden from view under the pants. This means the patient can be mobile and still enjoy normal social activities without others knowing about the indwelling catheter. The patient is taught to empty the bag when it is full, and to connect it to a larger bag overnight (night bag).
A catheter can be placed via the urethra (the tube that drains the bladder) or inserted surgically through the lower part of the abdomen directly into the bladder (suprapubic catheter – SPC). An SPC is often more comfortable for the patient and is easier to change compared to a urethral catheter.
Sacral neuromodulation (SNM, bladder pacemaker) is the only technology that may improve a patient’s ability to void. This is now covered by Medicare in those who have chronic urinary retention in the absence of obstruction, which has failed conservative treatments for more than 12 months.
SNM may not be suitable in some patients and initial work-up may be necessary. A 2-week trial is usually done to determine if someone may benefit from this. The response rate in patients with an underactive bladder is around 50% - 60% in those who have preserved bladder contractility (see A/Prof Gani’s publication on this below). Those with a totally acontractile or atonic bladder (complete loss of bladder function) have a much lower response rate (5% to 15%) during the trial.
Read A/Prof Gani’s publication - SNM has better results in patients with the underactive who still have preserved bladder contractility:
Download Evaluation of pre‑operative bladder contractility as a predictor of improved response rate to a staged trial of sacral neuromodulation in patients with detrusor underactivity - PDF (580 Kb)
Read A/Prof Gani’s publication - SNM is a reasonable treatment option for patients:
Download Sacral neuromodulation for detrusor hyperactivity with impaired contractility - PDF (1500 Kb)
Read A/Prof Gani’s publication:
Download Sacral neuromodulation in non obstructive urinary retention and painful bladder syndrome - PDF (257 Kb)
Read A/Prof Gani’s publication:
Download The underactive bladder diagnosis and surgical treatment options - PDF (895 Kb)
Read A/Prof Gani’s publication - A/Prof Gani was one of the first in the world to publish on:
Download Underactive bladder clinical features urodynamic parameters and treatment - PDF (296 Kb)