Dysfunction of the Anorectum - Incontinence

ESSENTIALS OF DIAGNOSIS

• Inability to control elimination of rectal contents.

• Characterization of rectal contents that are uncontrolled.

• Characterization of timing of incontinence.

General Considerations

Continence is dependent upon rectal compliance, anorectal sensation, anorectal reflexes, and anal sphincter function. The stool consistency (liquid versus solid) and quantity of stool also affect continence. The incidence of fecal incontinence is difficult to assess due to underreporting and lack of agreement as to what constitutes incontinence (eg, minor seepage versus complete incontinence). Although it is well accepted that incontinence is more commonly found in parous women, a high prevalence also occurs in men.

In women, the external sphincter is a thin band of muscle anteriorly, and thus especially susceptible to complete transection in this location resulting in incontinence. Obstetrical trauma during delivery may cause mechanical injury to the external sphincter. There is an increased incidence of incontinence after third-degree perineal tears, multiple vaginal deliveries, and infection of an episiotomy repair.

Neurogenic causes of incontinence include pudendal nerve stretch secondary to prolonged labor or to chronic straining during defecation. Vaginal deliveries are associated with reversible pudendal nerve injury in 80% of primagravida births. The injury may be unilateral or bilateral. If the nerve injury is permanent or is repeated multiple times, denervation and weakening of the external sphincter and pelvic floor result. The neuropathy and sphincter dysfunction progress because a weakened pelvic floor is unable to withstand increased intraabdominal pressure leading to further perineal descent and stretch injury. Similarly, descending perineum syndrome leads to cumulative stretch injury. Straining causes descent of the pelvic floor resulting in stretch of the pudendal nerve over the ischial spine.

Incontinence may also result from the treatment of perianal abscesses, fistula-in-ano, or perianal Crohn's disease due to disruption or division of the external sphincter.

Other causes of incontinence include systemic diseases affecting either the muscular or neurologic systems (eg, scleroderma, multiple sclerosis, dermatomyositis, and diabetes) or local anorectal problems (eg, radiation proctitis with fibrosis and decreased rectal compliance and tumors of the distal colon and rectum). Incontinence may also occur in people with normal anorectal neuromuscular function due to diarrhea or fecal impaction with overflow incontinence.

Clinical Findings

A. Symptoms and Signs It is important to distinguish complete incontinence (which has major social consequences and virtually always denotes a significant neurologic or muscular disorder) from . results in lack of control of gas, liquid, and solid stool. By contrast patients with partial incontinence have the ability to control solid stool but varying inability to control liquid stool and/or gas. Urgency, seepage, and soiling may occur regularly or intermittently, depending on the nature of the stool presenting to the rectum. Seepage of small amounts of fecal-stained mucus is extremely common with aging due to prolapsed hemorrhoidal tissue and inadequate dietary fiber. Soiling with urgency may be seen in patients with normal sphincteric function but a poorly distensible rectum due to proctitis or irritable bowel syndrome. However patients complaining of gross incontinence of solid fecal matter or an inability to sense stool until after incontinence has occurred often have a neurologic or muscular injury. Physical examination should include inspection and digital examination. On inspection, one should look for evidence of seepage or maceration of the perianal skin. The presence of external hemorrhoids or prolapsed internal hemorrhoids should be noted. Patients with gross incontinence may have a patulous anus. The anus should be inspected when the patient is instructed to squeeze: damage to the external sphincter may result in asymmetry or focal loss of corrugation of the anal verge. The patient should be instructed to perform a Valsalva to look for exaggerated descent of the perineum with straining or prolapse of hemorrhoidal tissue. Neurologic function is assessed grossly by looking for an anal wink and by testing for cutaneous pinprick sensation on both sides of the perianal gluteal region. Digital examination may detect a reduction in resting sphincter tone (primarily internal sphincter) or diminished voluntary squeeze pressures (primarily external sphincter).