Seminar

More than 200 million people worldwide live with incontinence. Given the magnitude of this disorder, primary care physicians should be encouraged to participate in the assessment and treatment of urinary incontinence (panel 1). Incontinence occurs frequently from middle age onwards and is associated with a reduced quality of life.1 The yearly direct cost of urinary incontinence in the USA alone is US$16·3 billion, of which three-quarters is for the management of women who have the condition.2 The Seminar aims to explain the mechanisms and the pathophysiology leading to incontinence, review the epidemiology, and provide a practical approach to the assessment and treatment of the disorder in women. Normal continence in women Normal continence in women is a complex coordination between the bladder, urethra, pelvic muscles, and surrounding connective tissues. Storage of urine is under voluntary control and modulated by the pontine micturition centre. The bladder is compliant through the range of physiological bladder filling (empty to capacity, typically 500–600 mL) and accommodates increasing urinary volume without increasing bladder pressure. This mechanical distension is unparalleled in any other organ and is accomplished by specialised function of the detrusor smooth muscle and neurological modulation.3 In infants, bladder fullness prompts a detrusor contraction that empties the bladder. With childhood bladder training, we learn to respond to the sensation of urge at volumes of 200–300 mL and make a decision about whether the time and place for voiding is appropriate.4 The urethra is 3–4 cm long and maintains sufficient pressure to prevent urine passage during times of physiological increases such as cough or physical activities. The skeletal muscle in the female urethra (rhabdosphincter) is composed of small, type I fibres located predominantly in the middle third region of the urethra. Urethral smooth muscle is deposited in longitudinal and circular layers. Both skeletal and smooth muscles contribute to resting tone, whereas skeletal muscle responds to rises in intra-abdominal pressures.5 Pelvic muscles are major contributors to continence. Levator ani contraction pulls the vagina forward toward the pubic symphysis, creating a backstop for the urinary tract. This stable backstop compresses the two walls of the urethra, thus preventing leakage of urine during cough or similar intra-abdominal increase