What is Female Stress Urinary Incontinence?
Stress urinary incontinence (SUI) is defined as leakage that occurs during activities that raise the intra-abdominal pressure (e.g. coughing, laughing, sneezing, lifting heavy objects). This can range from a few drops to a big gush, if severe.
The normal pelvic anatomy relating to the bladder
The urethra is the tube that drains the bladder to the outside. The bladder and the urethra are supported by layers of muscles and structures (pelvic floor) that lie underneath them. A strong pelvic floor is essential in normal continence; reflex tensioning of the pelvic floor provides counter-pressure to keep the urethra closed, during impact activities.
The sphincter is a ring of voluntary muscle that encircles the urethra. It squeezes tight when one does not want leakage to occur. During voiding, the sphincter relaxes to allow the urethra to open and let urine through.
What are the mechanisms and causes of SUI?
SUI is often due to a combination of urethral hypermobility and intrinsic sphincter deficiency (ISD) in variable proportions.
When there is a defect in the supporting pelvic floor, the urethra moves downwards from its resting position during activities such as laughing or coughing, and urine can leak through. This is called urethral hypermobility. Hypermobility-related incontinence implies the bladder outlet is closed at rest and opens during exertion.
Some causes are pregnancy, vaginal delivery, obesity, smoking, chronic cough, chronic constipation, high impact activity, genes, hysterectomy and certain anti-hypertensive drugs (alpha blockers).
Intrinsic sphincter deficiency (ISD)
ISD describes a urethral sphincter mechanism that lacks the co-aptation or normal closing pressure needed to prevent exertional leakage. In ISD, the bladder outlet is open at rest and urine can leak through even with lighter impact activities. The most severe form of ISD-related stress urinary incontinence is that of the fixed ‘lead-pipe’ urethra.
Causes include prior surgery, radiation, trauma with scarring or a neurologic condition.
In men who are incontinent after prostate surgery (see male stress urinary incontinence), the main mechanism is that of ISD because the sphincter is damaged from the surgery.
How common is it?
Up to 42% of women in their lifetime will complain of various degrees of stress urinary incontinence.
What other conditions can co-exist with SUI?
In women who have a concomitant prolapsed bladder, SUI may be masked or exacerbated.
It is quite common for patients to have both SUI and urge incontinence (see overactive bladder) at the same time and this is described as mixed incontinence.
How is SUI diagnosed?
Assessment would involve a detailed clinical history and in some patients, a physical examination can be very important. This is always done in the presence of a female chaperone.
Urinalysis can help rule out an infection as the cause of leakage.
A bladder diary can quantify the amount of fluid input and leakage. A 24-hour pad weight test can objectively measure the daily volume leaked.
Urodynamics (bladder pressure study) is appropriate in patients who are considering surgery to determine the severity of leakage and hence, the best surgical option for that particular patient. Urodynamics can also look for a component of overactive bladder and urge incontinence, which can improve with medications.
What are the treatments?
Patients are encouraged to make some lifestyle changes such as losing weight, treating constipation, reducing caffeine intake and to stop smoking.
Pelvic floor exercises were first described by Dr Arnold Kegel in the 1940s and they aim to strengthen the pelvic floor muscles and improve bladder neck support. A trained physiotherapist can assist in this.
Medications are usually not very helpful in treating SUI because the underlying problem is that of an anatomical failure.
Surgical options can be very effective in treating SUI. Surgery has changed a lot over the last 10 years with the advent of minimally invasive slings. Major surgery like the Burch colposuspension is no longer as popular as in the past. There are different types of slings; they differ:
In the way they are positioned (retropubic vs transobturator and mid-urethral vs bladder neck).
In the material that they are made of (synthetic vs own tissue).
The mid-urethral sling or the tension-free vaginal tape (TVT) is made of synthetic material and has excellent long-term results (70-80% cure rate at 10 years).
Patients typically stay in the hospital overnight and some can even be discharged on the same day. The sling can be positioned either retropubically (via a route behind the pubic bone) or transobturatorly (via the inner thighs). The surgery involves a 1cm vaginal incision and two other small stab incisions, either in the lower abdomen or in each inner thigh.
Overall complication rates are low and include bladder injury, infection, erosion of the mesh, inner leg pain, incorrect tensioning of sling, bowel and major blood vessel injuries (rare).
A retropubic sling can be made of synthetic material or it can be harvested from the patient’s own rectus fascia (layer of tough abdominal wall tissue).
The success rates are similar but the fascial sling has higher morbidity (longer hospital stay, bigger abdominal incision) but lower erosion and infection rates. The fascial sling is placed in a retropubic way, but sits more proximally at the bladder neck as compared to a mid-urethral sling (which is placed in the middle of the urethra). The fascial sling may be preferable in some patients.
Urethral bulking agents
This involves the injection of bulking agents into the urethra, creating wall-to-wall apposition and hence increasing the outlet resistance. Examples of agents that can be used are collagen (now no longer manufactured), Macroplastique (silicon particles in a viscous gel) and Bulkamid (hydrogel with synthetic polymer).
Success rates are lower at 30 - 50% and the procedure may need to be repeated. It can potentially be done under local anaesthesia and hence is suitable for frail, elderly patients. Some younger patients with mild incontinence who want the least invasive treatment, may also prefer this.
Cystoscopic view of the urethra: after injection