Outlet Dysfunction Constipation

Outlet dysfunction constipation (obstructed defecation) is difficulty evacuating stool due to functional or structural abnormality of the rectum and anal canal, despite adequate colonic transit.

• Functional causes: dyssynergic defecation (paradoxical puborectalis contraction, inadequate rectal propulsion), rectal hyposensitivity.
• Structural causes: rectocele, enterocele, rectal intussusception, rectal prolapse, sigmoidocele, anal stenosis, perineal descent, anismus after surgery.
• It accounts for up to half of patients with chronic constipation referred to tertiary clinics; women are affected more, especially after childbirth.

Excessive straining, sense of incomplete evacuation, anorectal blockage, need for digital manoeuvres (vaginal splinting, perineal pressure, digital extraction), need for enemas or suppositories, and prolonged toilet time.

• Stool consistency may be soft; urge may be absent.
• Digital rectal examination shows failure of the anal sphincter to relax or a paradoxical contraction during simulated evacuation, perineal descent, and a rectocele on posterior vaginal wall palpation.
• Differential diagnosis: slow transit constipation, constipation predominant irritable bowel syndrome, Hirschsprung disease, rectal cancer, stricture, hypothyroidism, hypercalcaemia, drug effects, spinal cord disease, pelvic mass.
• Complications: haemorrhoids, fissure, solitary rectal ulcer, rectal prolapse, faecal impaction, faecal incontinence, urinary symptoms, reduced quality of life.

Digital rectal examination during bearing down.

• Balloon expulsion test (normal expulsion of a 50 mL water-filled balloon within 1 minute).
• Anorectal manometry (high resolution) and surface electromyography to show dyssynergia.
• Defecography (barium or MR) to identify rectocele, intussusception, descent, enterocele.
• Colonic transit test (radio-opaque markers) to exclude coexisting slow transit.
• Colonoscopy if alarm features; bloods for thyroid function, calcium, glucose.

Supportive: toilet posture (squatting position with a footstool, trunk leaning forward), regular timing after meals, fibre 25 to 30 g daily, fluids, avoid straining beyond 5 minutes.

Pharmacological

• Osmotic laxatives: macrogol 17 g once or twice daily, or lactulose 15 to 30 mL twice daily.
• Stool softening suppositories: glycerol 4 g, bisacodyl 10 mg; sodium citrate micro-enema 5 mL before toileting.
• Prucalopride 2 mg daily (1 mg in age over 65 years or renal impairment) for coexisting slow transit.
• Botulinum toxin A 50 to 100 units into puborectalis is limited to short-term benefit.

Procedures

• Biofeedback pelvic floor retraining, once or twice weekly for 5 to 6 sessions, is the main treatment for functional disorders (success about 70 percent).
• Surgery for structural causes: transvaginal or transanal rectocele repair, laparoscopic ventral mesh rectopexy for intussusception, resection of redundant sigmoid.
• Sacral nerve stimulation in selected cases.

Special groups: post-partum women (pelvic floor physiotherapy), elderly (exclude impaction), men (exclude prostatic cause).

Red flags: new onset after age 50 years, rectal bleeding, weight loss, anaemia, stricture, neurological signs.

Follow-up: review at 6 to 8 weeks after biofeedback; repeat manometry if no improvement.