Porth's Essentials of Pathophysiology, 4e

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Disorders of the Bladder and Lower Urinary Tract

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the absence of urinary tract infection or other obvious pathology.” 25 The symptoms of urge incontinence, which are caused by involuntary bladder contractions dur- ing filling, may occur alone or in any combination. They constitute overactive bladder when they occur in the absence of other pathologic processes. 8,19,26–28 Regardless of the primary cause of overactive bladder, two types of mechanisms are thought to contribute to its symptomatology: those involving CNS and neural control of bladder sensation and emptying (neuro- genic) and those involving the smooth muscle of the bladder itself (myogenic). 8,26,27 The neurogenic theory for overactive bladder pro- poses that the CNS functions as an on–off switch- ing circuit for voluntary control of bladder function. Neurogenic causes of overactive bladder include stroke, Parkinson disease, and multiple sclerosis. Other neuro- genic causes of overactive bladder include increased sen- sitization of the afferent nerves that sense bladder filling or increased excitability to efferent nerves that produce bladder emptying. The myogenic causes of overactive bladder are thought to result from changes in the properties of the smooth muscle of the bladder itself. Bladder outlet obstruction can prompt such changes. It is hypothe- sized that the sustained increase in intravesical pressure that occurs with the outlet obstruction causes a partial destruction of the nerve endings that control bladder excitability. 7 This partial denervation produces hyper- excitability of the detrusor muscle, causing urgency and frequency of urination due to spontaneous bladder contractions. Disorders of detrusor muscle structure and excitability also can occur as the result of the aging process or disease conditions such as diabetes melli- tus. Incomplete bladder emptying, a common accom- paniment of overactive bladder, often exacerbates symptoms. Overflow Incontinence. Overflow incontinence is an involuntary loss of urine that occurs when intravesical pressure exceeds the maximal urethral pressure because of bladder distention in the absence of detrusor activ- ity. 8 It can occur with retention of urine owing to ner- vous system lesions or obstruction of the bladder neck or urethral stricture. Outflow obstruction may occur secondary to cystocele, uterine prolapse, or previous incontinence surgery in women. In men, one of the most common causes of obstructive incontinence is enlarge- ment of the prostate gland. Person with this type of incontinence may experience dribbling, weak urinary stream, hesitancy, frequency, and nocturia. Other Causes of Incontinence. Other causes of incontinence include decreased bladder compliance or distensibility. This abnormal bladder condition may result from radiation therapy, radical pelvic surgery, or interstitial cystitis. Many persons with this disor- der have severe urgency related to bladder hypersen- sitivity that results in loss of bladder elasticity, such that any small increase in bladder volume or detrusor

function causes a sharp rise in bladder pressure and severe urgency. Incontinence may occur as a transient and correct- able phenomenon, or it may not be totally correct- able and may occur with various degrees of frequency. Incontinence may also present as nocturnal enuresis with involuntary loss of urine during sleep, as post-micturi- tion dribble, or continuous urine leakage. 18 Among the transient causes of urinary incontinence are recurrent urinary tract infections; medications that alter bladder function or perception of bladder filling and the need to urinate; diuretics and conditions that increase blad- der filling; restricted mobility; and a state of confusion. Night sedation may cause someone to sleep through the signal that normally would waken them so they could get up and empty their bladder and avoid wetting the bed. Incontinence also may be caused by factors outside the lower urinary tract, such as the inability to locate, reach, or receive assistance in reaching an appropriate place to void. Diagnosis andTreatment Urinary incontinence is not a single disease but a symp- tom with many possible causes. As a symptom, it requires full investigation to establish its cause. 20–24,27 This usually is accomplished through a careful history, physical exam- ination, blood tests, and urinalysis. A voiding record (i.e., diary) may be used to determine the frequency, timing, and amount of voiding, as well as other factors associated with the incontinence. Because many drugs affect blad- der function, a full drug history is essential. Estimation of the PVR volume is recommended for all persons with incontinence. Treatment or management depends on the type of incontinence, accompanying health problems, and the person’s age. It includes behavioral methods; exercises to strengthen the pelvic floor muscles; pharmacologic measures; surgical interventions; and, when urine flow cannot be controlled, noncatheter devices to obstruct urine flow or collect urine as it is passed. 28,29 Indwelling catheters, although a solution to the problem of urinary incontinence, usually are considered only after all other treatment methods have failed. In some types of incon- tinence, such as that associated with spinal cord injury or meningomyelocele, self-catheterization may provide the best means for controlling urine elimination (see Chapter 36). Behavioral methods include fluid management, timed/prompted voiding, bladder retraining, and toi- leting assistance. Bladder retraining and biofeedback techniques seek to reestablish cortical control over blad- der function by having the person ignore urgency and respond only to cortical signals during waking hours. Exercises of the pelvic muscles or Kegel exercises involve repetitive contraction and relaxation of the pelvic floor muscles and are an essential component of patient- dependent behavioral interventions. 19 Pharmacologic treatment is aimed at using drugs to alter the physiologic mechanisms that contribute to the neurogenic or myogenic causes of incontinence