Urge incontinence

Alternative names:

detrusor instability; irritable bladder; spasmodic bladder; unstable bladder; urgency incontinence

Definition:

A condition characterized by a strong desire to urinate immediately before an involuntary bladder contraction with a loss of a large amount of urine.

Causes, incidence, and risk factors:

NORMAL URINATION:
The ability to hold urine and maintain continence is dependent on normal function of the lower urinary tract, the kidneys, and the nervous system. Additionally, the person must possess the physical and psychological ability to recognize and appropriately respond to the urge to urinate.

The process of urination involves two phases: 1) the filling and storage phase, and 2) the emptying phase. Normally during the filling and storage phase, the bladder begins to fill with urine from the kidneys. The bladder stretches to accommodate the increasing amounts of urine. The first sensation of the need to urinate occurs when approximately 200 ml of urine is stored. The healthy nervous system will respond to this stretching sensation by alerting you to the need to urinate while also allowing the bladder to continue to fill. The average person can hold approximately 350 to 450 ml of urine. The ability to fill and store urine properly requires a functional sphincter (muscle controlling output of urine from bladder) and a stable bladder wall muscle (detrusor).

The emptying phase requires the ability of the detrusor muscle to appropriately contract to force urine out of the bladder. Additionally, the body must also be able to simultaneously relax the sphincter to allow the urine to pass out of the body.

During infancy, the bladder contracts automatically when a certain volume of urine is reached within its walls. As an individual learns to control urination, bladder muscle contraction is prevented by constant inhibition from the brain (cerebral cortex) as the individual consciously delays urination. Undesired bladder muscle contraction may occur as the result of a break in the neurological pathway from the cerebral cortex to the bladder. It can also occur if the bladder is so irritable that the normal inhibitory neurological impulses (messages that slow down or prevent an action) are insufficient to keep the bladder muscle relaxed as urine fills the bladder.

URGE INCONTINENCE:
Urge incontinence is basically a storage problem in which the bladder muscle contracts inappropriately. Often these contractions occur regardless of the amount of urine that is in the bladder. Urge incontinence may result from neurological injuries (such as spinal cord injury or stroke), neurological diseases (such as multiple sclerosis), infection, bladder cancer, bladder stones, bladder inflammation, or bladder outlet obstruction (enlarged prostate). However, the majority of cases are classified as idiopathic--a specific cause cannot be identified.

Irritable bladder may occur in either males or females at any age, however it is more common in women and the elderly. It is second only to stress incontinence as the most common cause of urinary incontinence (involuntary loss of urine). Approximately 1 to 2% of the adult females are affected by the problem.