Clinical overview
Urinary incontinence (UI), defined by the International Continence Society as the complaint of any involuntary loss of urine, is one of the most prevalent conditions in women's health, affecting a substantial minority of adult women and a majority of the elderly and parous. It is chronically under-reported — out of embarrassment, and from the mistaken belief that leakage is an inevitable consequence of childbearing or ageing — yet it is rarely dangerous and almost always improvable. Its impact is on dignity, work, physical activity, sexual function and mental health, and the burden of containment (pads, restricted fluids, "toilet-mapping") is itself disabling.
This is an HOTS objective focused on classification, definitions and pathophysiology, because correct classification is the clinical work: the type of incontinence dictates the entire management pathway, and the commonest errors are pathophysiological mislabels — treating overflow as overactive bladder, or treating a fistula as stress incontinence. The two dominant types are stress urinary incontinence (SUI) — leakage on effort or exertion — and urgency urinary incontinence (UUI), the key storage symptom of the overactive bladder (OAB) syndrome; many women have mixed UI. Two further patterns must always be actively excluded because they are managed entirely differently: overflow incontinence from chronic retention (Urinary retention) and continuous incontinence, which should always raise the suspicion of a fistula (Gynaecological fistulas). This chapter sets out the continence mechanism, the definitions and classification, the pathophysiology of each type, and the NICE-based stepped management — reshaped in recent years by the national pause on vaginal mesh. It links to Genital prolapse (which frequently coexists) and Climacteric and menopause (genitourinary atrophy).
Core knowledge
Definitions (ICS)
- Stress UI — involuntary leakage on effort/exertion or on sneezing/coughing.
- Urgency UI — involuntary leakage accompanied by, or immediately preceded by, urgency (a sudden compelling desire to void that is difficult to defer).
- Mixed UI — both of the above.
- Overactive bladder (OAB) syndrome — urgency, usually with frequency (≥8 voids/day) and nocturia, with (OAB-wet) or without (OAB-dry) urgency incontinence, in the absence of infection or other obvious pathology.
- Overflow incontinence — leakage from a chronically over-distended, poorly emptying bladder.
- Continuous incontinence — constant leakage, classically from a fistula or an ectopic ureter.
The continence mechanism
Figure C2.1 — Why continence fails: the pressure balance (urethral closure vs detrusor pressure), and the mechanisms of stress, urgency/OAB, overflow, mixed and continuous (fistula/ectopic ureter) incontinence.
Continence is maintained whenever urethral closure pressure exceeds intravesical (detrusor) pressure, both at rest and during rises in intra-abdominal pressure. The contributors:
- Urethral support — the anterior vaginal wall and its attachments (the pubourethral ligaments and the levator-ani "hammock", as described by DeLancey) provide a firm backboard against which the urethra is compressed when abdominal pressure rises (the pressure-transmission and integral theories). Intact support means a cough is transmitted equally to bladder and urethra, preserving the pressure gradient.
- Intrinsic sphincter — the smooth and striated urethral musculature and urethral wall tone generate the maximum urethral closure pressure (MUCP) at rest.
- Mucosal coaptation and the submucosal vascular plexus — seal the urethral lumen; both are oestrogen-dependent, which is why genitourinary atrophy worsens symptoms after the menopause (Climacteric and menopause).