Female Incontinence: Classification & Definitions

Urinary incontinence is an extremely common problem that affects people in the United States and worldwide.  For women, urinary incontinence is relatively uncommon early in life, has a peak around menopause and then continues to rise for women into their 80's.  It is estimated that 20-30% of young adult women, 30-40% of middle-aged women and 30-50% of elderly women have incontinence.[1]

Normal Voiding

While the bladder fills with urine, pressure remains stable due to intrinsic properties of the bladder.  The ability of the bladder to maintain a stable pressure is based on natural viscoelastic properties of the bladder wall and receptors within the bladder that help it relax and accommodate as it fills.  Stable pressures contribute to continence; in addition, normal anatomic pelvic support, an intact urinary sphincter and neural control of the storage and voiding process are essential.

When the bladder is full, a complex neurological process  consisting of conscious and unconscious activity -  allows normal voiding.  Once volitionally committed to voiding, the striated sphincter relaxes followed by increasing detrusor activity leading to increased bladder pressures.  Once the proximal urethra and bladder neck open, voiding begins.

In men, the bladder neck is intimately associated with the prostate and provides an additional component of continence.  In women, there is no bladder neck mechanism and continence relies solely on the urethral sphincter which is composed of a layer of longitudinal intrinsic urethral smooth muscle and a larger extrinsic striated muscle that extends throughout the proximal 2/3rds of urethra.  Continence therefore relies on watertight apposition of the urethral lumen and external compression of the lumen by the external muscle.  Finally, adequate structural support by the pelvic floor musculature is required to keep the urethra from moving during increases in abdominal pressure.

Classification of Urinary Incontinence

Incontinence is classified into a number of categories that are not mutually exclusive:

• stress urinary incontinence
• urgency urge incontinence
• mixed (stress/urge) incontinence
• mixed symptoms
• overflow incontinence
• extraurethral incontinence
• occult/latent stress incontinence
• situational incontinence
• nocturnal enuresis

Wein AJ, Rackley RR. Overactive bladder: a better understanding of pathophysiology,
diagnosis and management. J Urol 2006;175:S5–10.

Stress Urinary Incontinence (SUI)

SUI refers to the involuntary leakage of urine with exertion, usually cough, sneeze or straining.  On examination, leakage can be viewed with increasing abdominal pressure without bladder contractions.  The etiology of SUI can be considered related to hypermobility (due to loss of strength or function of pelvic support structures) or intrinsic sphincter deficiency.  Risk factors for SUI can be considered by etiology and include:

URETHRAL HYPERMOBILITY

• Pregnancy
• Multiparity
• Vaginal delivery (direct injury to pelvic soft tissues and partial denervation of pelvic floor)
• Forceps delivery
• Third-degree perineal tear
• Increased duration of labor
• High birth weight (>4000 g=8lb 13oz)
• Chronic abdominal straining
• Neurologic injury (specifically pudendal nerve injury)

INTRINSIC SPHINCTER DEFICIENCY

• Previous urethral or periurethral surgery 
• Neurologic insult
• Surgical: hysterectomy or other pelvic surgeries
• Medical: multiple sclerosis, diabetic neuropathy
• Pelvic radiation: can affect neurologic function or damage local tissues leading to poor co-aptation of the urethra 

Urgency Urge Incontinence (UUI)

UUI refers to the involuntary leakage of urine accompanied by or immediately preceded by a sense of urgency.[2]  Patients often complain of frequent small losses of urine between micturitions or catastrophic leak with complete bladder emptying.  

UI may be related to, but is not the same as Overactive Bladder (OAB).  OAB, also known as the urgency frequency symptom syndrome, refers specifically to a clinical constellation of urgency, with or without incontinence, frequency and nocturia.[3]  Overactivity can vary in severity and symptoms among patients.  Some patients demonstrate phasic detrusor activity, which describes strong contractions as the bladder fills and may or may not lead to incontinence.  In contrast, terminal detrusor activity refers to a single, involuntary contraction of the bladder at maximal capacity that leads to incontinence and is most commonly seen in elderly patients or those with neurologic compromise.  

Mixed Urinary Incontinence (MUI)

MUI refers to the combination of SUI and UI symptoms; a patient may have involuntary leakage with urgency AND with exertion.  40% of women with SUI will have mixed, OAB symptoms.  

Other Types of Incontinence

Overflow incontinence: leakage of urine associated with urinary retention

Extraurethral incontinence: urine leakage through channels other than the urethra (e.g., fistula or ectopic ureter)

Occult/Latent stress incontinence: Masked by prolapse, evident on reduction of prolapse

Situational incontinence: coital (incontinence with sexual intercourse), giggle incontinence

Nocturnal enuresis: loss of urine occurring during sleep

Later blog entries will focus on the evaluation and management of incontinence in men and women.

[1] Nitti. The Prevalence of Urinary Incontinence.  Rev Urol. 2001; 3(Suppl 1): S2–S6.
[2] Abrams P, Artibani W, Cardozo L,et al: Reviewing the ICS 2002 terminology report: the ongoing debate. Neurourol Urodyn 2009; 28: 287
[3] Chapple CR, Artibani W, Cardozo LD, et al. The role of urinary urgency and its measurement in the overactive bladder symptom syndrome: current concepts and future prospects. BJU Int 2005;95:335–40

Other resources for understanding incontinence include:
Chapple and Milsom.  Chapter 63: Urinary Incontinence and Pelvic Prolapse in Campbell-Walsh Urology , Tenth Edition. Eds, Wein, Kavoussi, Novick, Partin, Peters.  2012.

Abrams P: ICS standardization documents. 2002
http://www.icsoffice.org/ASPNET_Membership/Membership/Documents/Documents.aspx