Urinary incontinence is defined by the International Continence Society (ICS) as “the complaint of involuntary leakage of urine.” The most common forms of urinary incontinence are classified as stress, urgency, and mixed urinary incontinence. The current ICS definition of stress urinary incontinence (SUI) is subjective based on symptoms perceived by the patient: “stress urinary incontinence is the complaint of involuntary leakage on effort or exertion, or on sneezing or coughing.”1 In contrast, urgency urinary incontinence is “the complaint of involuntary leakage accompanied by or immediately preceded by urgency,” and mixed urinary incontinence is “a combination of symptoms of both stress and urgency urinary incontinence.”
The definition of SUI has evolved over time into its current subjective definition. It was previously referred to as “genuine stress incontinence (GSI)” by the 1990 ICS Standardization of Terminology of Lower Urinary Tract Function. GSI was defined as “the involuntary loss of urine occurring when, in the absence of a detrusor contraction, the intravesical pressure exceeds the maximum urethral pressure.” With the revision of the ICS terminology in 2002, GSI was replaced by the term “urodynamic stress incontinence.” Urodynamic stress incontinence is the observation during filling cystometry of involuntary leaking of urine during increased abdominal pressure, in the absence of a detrusor contraction. The evolution of the definition of SUI underlines the importance of eliciting the patients’ subjective experience of the condition.
Closure of the urethra is essential during filling and storage of urine in order to prevent leakage. If the urethral closure mechanism is incompetent, it allows leakage of urine in the absence of a detrusor contraction. Both intrinsic and extrinsic factors contribute to the symptoms of SUI. Intrinsic factors are those related to the function of the urethra, whereas extrinsic factors are secondary to influences apart from the urethra, such as patient level of activity or weight and urethral support. Increasingly rigorous investigation into the epidemiology, anatomy, physiology, and neurology of SUI has promoted the understanding of normal and incontinent states; this chapter provides an overview of current understanding of these mechanisms, as well as their limitations.
Prevalence rates for SUI are wide, with reported ranges from as low as 4% to as high as 70%,2 and vary by age. SUI is common in younger women with estimated rates of 4% to 23% in women age 20 to 39 years. Prevalence rates peak by age 50 to 60 years, with estimated rates of 16% to 36% in women age 40 to 59 years.2 Older women are more likely to be affected by urgency urinary incontinence and mixed urinary incontinence than SUI.
Multiple studies report different prevalence rates of urinary incontinence between different racial groups. African-American women are less affected by SUI compared to Caucasian women, with one population-based study showing prevalence rates of SUI in Caucasian women of 39.2% compared to 25.0% in African-American women...