Intrinsic sphincter deficiency (ISD) is a condition where the urethral sphincter, the muscle that keeps urine from leaking out of the bladder, no longer closes tightly enough to maintain a seal. Unlike the more common form of stress urinary incontinence caused by a mobile or poorly supported urethra, ISD means the sphincter itself is weak or damaged. This distinction matters because ISD tends to cause more severe leakage and is harder to treat successfully.
How ISD Differs From Other Stress Incontinence
Stress urinary incontinence has two main causes, and they sometimes overlap. The first is urethral hypermobility, where the urethra and bladder neck shift out of position during physical effort like coughing or jumping. The pelvic floor muscles and tissues that normally hold everything in place have weakened, so the urethra drops and can’t stay shut under pressure. The sphincter itself works fine; it just isn’t being supported properly.
ISD is fundamentally different. The urethra often stays in a relatively fixed position, but the sphincter muscle can’t generate enough closing force on its own. People with ISD may leak urine with very little physical effort, sometimes just from standing up or walking. In severe cases, leakage can happen with almost no increase in abdominal pressure at all, essentially a gravity-driven drip. This is a key clinical clue: if incontinence occurs during minimal activity rather than only during coughing, sneezing, or heavy lifting, ISD is more likely.
Many women have elements of both problems, but treatment planning depends on identifying which mechanism is dominant.
Common Causes and Risk Factors
ISD develops when the sphincter tissue itself is damaged or deteriorates. The most common causes include prior pelvic or incontinence surgery, where scar tissue replaces the normal muscle and connective tissue around the urethra. Among women who have had two or more failed surgeries for stress incontinence, ISD is present in up to 75% of cases. Radiation therapy to the pelvis, neurological conditions that impair the nerves controlling the sphincter, and aging-related tissue thinning (especially after menopause, when estrogen levels drop) also contribute. Severe pelvic trauma or prolonged difficult childbirth can damage the sphincter directly.
How ISD Is Diagnosed
Diagnosis typically combines a physical exam with a specialized pressure test called urodynamic testing. During the exam, a clinician looks for visible urine loss when you bear down or cough, and checks whether the urethra moves significantly. A relatively fixed urethra that still leaks is a hallmark finding.
Two measurements help confirm the diagnosis. The first is the Valsalva Leak Point Pressure (VLPP), which measures how much abdominal pressure it takes to force urine past the sphincter. A VLPP of 60 cm of water or less indicates ISD. Values between 60 and 90 fall into a gray zone, while values above 90 suggest the problem is urethral hypermobility rather than a weak sphincter. The second measurement, Maximal Urethral Closure Pressure (MUCP), assesses the sphincter’s resting squeeze force. A value below 20 cm of water points toward ISD.
These numbers aren’t perfect, and some clinicians rely more on one than the other. But taken together with the history and physical exam, they paint a clear enough picture to guide treatment decisions.
Why ISD Is Harder to Treat
Standard incontinence procedures work largely by repositioning or supporting the urethra. When the sphincter itself is the weak link, simply propping the urethra back into place doesn’t solve the core problem. Surgical success rates for ISD are consistently lower than for urethral hypermobility across virtually every procedure studied. This doesn’t mean treatment fails, but expectations should be realistic, and the choice of procedure matters more.
Sling Surgery for ISD
Sling procedures, which place a strip of material under the urethra to compress it and restore resistance, are the most widely used surgical option. For ISD specifically, slings placed through a retropubic approach (running behind the pubic bone) perform better than those threaded through a transobturator route (running through the inner thigh). Multiple studies show a statistically significant advantage for the retropubic path in ISD patients, though even with this approach, success rates fall well below what’s achieved when treating pure urethral hypermobility.
The sling material also matters. For women who have had prior mesh complications, urethral erosion, or fistula repair, a sling made from the patient’s own tissue (usually a strip of abdominal fascia) is preferred over synthetic mesh. This autologous fascial sling has better short-term and long-term outcomes with fewer complications in these higher-risk patients.
Urethral Bulking Agents
Bulking agents are injectable gels placed around the urethra in an office or outpatient setting to add volume and help the sphincter close. The procedure is minimally invasive and doesn’t require general anesthesia, making it appealing for women who want to avoid or aren’t candidates for surgery.
Short-term results can be encouraging. One multicenter study found subjective and objective cure rates of 81% and 83% at three years. However, the effect tends to diminish over time. Long-term follow-ups at seven to eight years show cure or improvement rates dropping to around 65%, with subjective success falling to about 53%. A second injection is needed in roughly 30 to 40% of cases, and some studies report re-injection rates as high as 77%. The median gap between injections is about three months.
Bulking agents work best as a first-line option for mild to moderate ISD, or for women who have already had sling surgery and still leak. Overall success rates are lower than with slings, and many patients eventually need a follow-up procedure.
Artificial Urinary Sphincter
For severe ISD that hasn’t responded to other treatments, an artificial urinary sphincter (AUS) is an option. This implanted device consists of a fluid-filled cuff that wraps around the urethra, keeping it closed until you’re ready to urinate. You activate a small pump placed under the skin to temporarily open the cuff, then it automatically re-inflates after a few minutes.
The AUS is considered the gold standard for moderate to severe stress incontinence in certain populations, particularly men after prostate surgery, and it’s also used for ISD in people with neurological conditions. Functional continence (defined as using one pad or fewer per day) is reported in 75 to 90% of patients. One long-term study with a median follow-up of over 17 years found that 90% of patients maintained adequate continence. A separate multicenter study at about seven years of follow-up reported 74% of patients with an AUS still in place had good continence.
The trade-off is that the device is mechanical and may eventually need revision or replacement. It also requires the ability to operate the pump manually, which can be a limitation for people with impaired hand function.
Living With ISD
Pelvic floor physical therapy, while less likely to fully resolve ISD compared to hypermobility-type incontinence, can still improve symptoms by strengthening the surrounding muscles that assist the sphincter. Timed voiding, where you empty your bladder on a schedule before it gets too full, reduces the pressure the sphincter has to resist. Maintaining a healthy weight lowers chronic abdominal pressure, and avoiding known bladder irritants like caffeine and alcohol can reduce urgency that compounds the problem.
Because ISD often coexists with prior surgical history or other pelvic floor issues, treatment is rarely one-and-done. Many women go through a progression of therapies, starting with conservative approaches, moving to bulking agents, and potentially advancing to sling surgery or an artificial sphincter if needed. Understanding that ISD is a sphincter-strength problem, not just a support problem, helps you have more productive conversations about which options are most likely to work for your specific situation.