What is Underactive Bladder?
An underactive bladder 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.
What causes it?
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 have 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. There is often a sense of incomplete bladder emptying and patients would revisit the toilet soon after leaving it.
Because the patient does not fully empty the bladder, it does not take long for the bladder to fill up again and cause ‘overflow’ incontinence. This type of leakage often occurs all throughout the day with the patient being unaware. When full, a normal bladder would send signals to the brain, but if the bladder has also lost some sensation, these signals are not sent and hence, the leakage would occur with no warning. In these patients, they may have less urge to urinate and can go for 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 can cause symptoms like poor, interrupted urinary flow, urinary frequency and blood in the urine.
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-catheterization (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 gives an idea of how well the bladder can contract.
Urinary flow rate
Measurements of urinary flow rate and post-void bladder scan 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 would be 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 pressure study)
Urodynamics is very useful in diagnosing the underactive bladder. Patients would 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 would 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. To empty the bladder, some form of catheterization must be instituted.
Intermittent self catheterization (ISC):
In those who still have good hand-eye coordination, intermittent self-catheterization (ISC) can be taught. Here patients are taught to self-insert a small catheter into the bladder to drain it at regular intervals. They 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 district nurse. The catheter is connected to a bag that is attached to the leg and can be hidden from view under the pants. The patient is taught to empty the bag when it is full, and to connect it to a larger bag overnight.
A catheter can be placed via the urethra (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.
A relatively new treatment option is also available – see sacral neuromodulation (bladder pacemaker). 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. Sacral neuromodulation also works in patients with the opposite of an underactive bladder (i.e. those with overactive bladder).
The response rate in patients with an underactive bladder is lower than that of an overactive bladder and is around 50%. In general, those who retain some degree of bladder contractility tend to respond better to sacral neuromodulation.