Imagine a scenario where a hearty laugh or a simple sneeze results in an unexpected consequence: involuntary release of urine. Whilst it is understandably inconvenient or frustrating, over 300 million people worldwide are affected by urinary incontinence (UI); the majority of which are women¹. As it may have implications on people’s quality of life, it is important to understand what stress incontinence is and what the underlying mechanisms are. In this article, we will delve into what you should know about stress incontinence.

What is urinary incontinence?

Incontinence refers to the involuntary passing of bodily products, mainly urine or faeces – this is known as urinary or faecal incontinence, respectively. Urinary incontinence (UI) is very common but may present differently and thus there are various types of UI. The commonest form is stress incontinence, which largely affects women, and will be the focus of this article.² However, other types of urinary incontinence are important to be aware of as they can often be conflated with stress incontinence, these include urge incontinence and overflow incontinence. The clinical presentation and the situations/events associated with the incontinence episodes reflect the type of urinary incontinence, as the underlying mechanisms will be different. 

Our kidneys are connected to a urinary bladder via the ureters, which act as a conduit for urine to flow through them and enter the bladder. Urine is stored in the bladder before its release through the urethra. It is important to note several anatomical features that are of relevance to incontinence:

1. The urinary bladder contains muscle tissue, which allows for contraction of the bladder. When contraction occurs, the pressure inside the bladder increases, which forces the contents (urine) out of the bladder. This leads to urination.
2. Sphincters are rings of muscle that are located in several areas of the urinary tract to control the flow of urine. Think of sphincters as checkpoints – when the ring of muscle is closed, the structure that urine is passing through will also be blocked, thus stopping urine from flowing. There are several sphincters, such as the internal and external urethral sphincters. The internal sphincter sits at the junction between the bladder and the urethra.
3. The urinary bladder is located in the pelvis and sits above the pelvic diaphragm. The pelvic diaphragm is a term used to describe a group of muscles that form the floor of your pelvic cavity. In women and individuals with a uterus, the uterus naturally bends towards the bladder and may partially sit on it (hence why pregnancy or menstruation can lead to increased frequency of urination, as there is more pressure).

The above points aid in understanding the mechanism of urinary incontinence.³ If the nerve supply to the bladder is affected, there may be inappropriate contraction/relaxation of the bladder, as well as sensations of urgency. If the sphincters are weak, there is less control over the flow of urine. If structures surrounding the bladder are abnormal, urgency and involuntary urination are possible. The urinary bladder can, on average, store 500 ml of urine and an individual may feel the need to urinate once the volume is 200-300 ml.⁴ 

Mechanism of stress incontinence

Stress incontinence occurs when urine leaks out during activities/situations that lead to increased pressure inside the body and is due to an incompetent sphincter or weak pelvic floor muscles. For example, sneezing, coughing, laughing, straining and strenuous exercise. A common misunderstanding is that stress incontinence is associated with urgency, but this is not true. A sensation of urgency leading to incontinence is typical of another type of incontinence – urge incontinence. The diagnosis of stress incontinence is therefore a clinical one. There should be no/minimal features of urgency and identification of trigger episodes/events associated with the incontinence. The diagnosis itself does not rely on the volume of urine involuntarily leaked; however, a typical presentation involves small and frequent urine losses. Major risk factors include increasing age and BMI. 

Causes

• Pregnancy – During pregnancy, the uterus expands, and this increases the pressure on several pelvic structures: bladder, urethra, and pelvic floor muscles/ pelvic diaphragm.
• Childbirth – Stress incontinence is more likely to occur in vaginal births than in caesarean sections, as there may be damage or excess stress on the pelvic floor muscles, during delivery. 
• Hormonal changes – This is seen particularly in menopause and perimenopause. A fall in oestrogen can lead to thinning of the lining of the urethra. Alternatively, urogenital prolapses can occur secondary to menopause, which may also be associated with urinary incontinence.
• Obesity – As mentioned for pregnancy, things that increase pressure on your abdomen can potentially weaken pelvic floor muscles and lead to insufficiency of the sphincter.

Investigations

• Bladder diary – you may be given a chart, which will allow you to keep a record of how much fluid you take in a day when you take fluids and the amount of urine you pass each time you go to the toilet. This is usually done for about 3 days, and you can record other things, such as incontinence episodes.
• Urine dipstick/ urinalysis – A sample of urine is taken and is tested on a strip for infection, blood, or any other abnormalities (e.g., protein in urine)
• Post-void residual bladder volume – This may also be named, voiding studies. This is an ultrasound scan of the bladder, to check the amount of urine left in the bladder after voiding.
• Urodynamic testing – This is a more advanced test and is not commonly offered for patients with obvious cases of stress/urge/mixed incontinence. 

Management

Conservative

Management can be broadly classified into conservative, medical and surgical. Where patients have mixed incontinence, i.e., urge and stress types of UI, the predominant type is treated/addressed first. Conservative management largely involves lifestyle changes and incorporating habits and exercises that will target the cause of the incontinence. It is usually the first-line management that you will  receive by your doctor.⁵ Conservative management is essential in many cases of stress incontinence. This often includes monitoring fluid intake, weight loss and pelvic floor exercises. Trained healthcare professionals will advise patients on how to carry out the exercises and how often. The National Institute for Health and Care Excellence (NICE), recommends at least 8 contractions performed 3 times a day, for a minimum of 3 months.⁶ Pelvic floor exercises can also be done by pregnant women. Conveniently, there are many videos online that aid patients with performing pelvic floor exercises. Although you may feel that conservative management does not bring about an immediate effect/improvement in the symptoms, many patients who are compliant with their management plan, are able to resolve their symptoms without the need to use medications or have surgical interventions, which can have side effects and complications. 

Surgical

If pelvic floor exercises and other conservative measures are unsuccessful, another management option would be surgery.⁷ The purpose of this is to alter and readjust the position of the bladder and/or urethra to alleviate symptoms. It is also possible for surgery to target other structures, depending on the cause of the stress incontinence, e.g., urogenital prolapse. There is an array of surgeries that can be performed, but Tension-free vaginal tape (TVT) is a common and more modern procedure with a high success rate. It is carried out via the vagina and under local anaesthetic, which allows for this surgery to be done as an outpatient procedure in many centres. You may also come across sling procedures, which are very effective but have been superseded by TVT in recent years, due to a slightly higher side effect profile. The role of the sling procedure is to lift part of the urethra and attach it to the abdominal wall, which reduces incontinence. A larger operation that can be performed for stress incontinence is colposuspension. This may be indicated in patients with urogenital prolapse or in more complex cases of stress incontinence. The surgery involves attaching the bladder to the posterior abdominal wall. Whilst it is more effective than a sling procedure, it has several potential complications and also means that individuals will not be able to conceive thereafter.

Medical

Currently, the medication licensed for stress incontinence is duloxetine. You may know this as an antidepressant, but given the drug mechanism, it can also relieve symptoms of stress incontinence in around 50% of cases.⁷ As it has several significant side effects, like nausea and vomiting, it is not usually the second-line treatment option. Patients may be prescribed duloxetine if they decline surgical options. In the case of urogenital prolapse and post-menopausal individuals, ring pessaries may alleviate the symptoms of stress incontinence.

Summary

Urinary incontinence is a frequent presentation in primary care and stress incontinence is the commonest type. It predominantly affects women, due to risk factors such as pregnancy, vaginal deliveries, and obesity. An inadequate sphincter leads to the symptoms of involuntary urine loss during activities that increase intra-abdominal pressure, like coughing. Pelvic floor exercises are the mainstay management plan but other options such as surgical procedures may alleviate symptoms in other cases.