Chronic Constipation & Fecal Incontinence
Screen for alarms and culprits, climb the laxative ladder, then test the outlet
Definition and first evaluation
Rome IV functional constipation. Two or more of the following for the last 3 months, with onset at least 6 months earlier: straining, lumpy or hard stools, a sense of incomplete evacuation, a sense of anorectal blockage, or manual maneuvers (digital evacuation, perineal support)—each in more than a quarter of defecations—or fewer than 3 spontaneous bowel movements per week. Loose stools are rare without laxatives, and IBS criteria are not met. When abdominal pain linked to defecation dominates (at least 1 day per week), the label is IBS with constipation; the two lie on a spectrum.
Alarm features. Colonoscopy is indicated for:
- Hematochezia or a positive fecal immunochemical test
- Unintentional weight loss or iron-deficiency anemia
- Family history of colorectal cancer or inflammatory bowel disease
- New-onset constipation or change in bowel habit in an older adult
- Overdue colorectal cancer screening
Everyone else. Without alarms, colonoscopy adds nothing beyond age-appropriate screening. A limited panel—CBC, TSH, calcium and glucose—screens for anemia and the common metabolic causes. The digital rectal exam is essential: it finds fissures, masses, impaction and paradoxical sphincter contraction on bearing down.
Secondary causes
| Category | Examples |
|---|---|
| Medications | Opioids; anticholinergics (TCAs, first-generation antihistamines, antipsychotics, oxybutynin); verapamil; iron; aluminum- and calcium-containing antacids; clonidine; ondansetron; bile acid sequestrants |
| Endocrine and metabolic | Hypothyroidism, hypercalcemia, hypokalemia, diabetes with autonomic neuropathy, pregnancy |
| Neurologic | Parkinson disease, multiple sclerosis, spinal cord injury or lesions, Hirschsprung disease (children) |
| Structural | Colorectal cancer, strictures, anal fissure (painful withholding), rectocele |
Verapamil is by far the most constipating calcium channel blocker; dihydropyridines such as amlodipine cause much less. Stopping or swapping a culprit drug beats adding a laxative.
Stepwise treatment
- Lifestyle and fiberFiber to 20–35 g/day (soluble psyllium preferred) with fluids; sit on the toilet after meals to use the gastrocolic reflex, feet raised on a stool.
- Osmotic laxativePolyethylene glycol 3350, 17 g daily.
- Stimulant laxativeSenna or bisacodyl, added or as rescue.
- Secretagogue or prokineticLinaclotide, plecanatide, lubiprostone or prucalopride.
- Physiologic testingAnorectal manometry and balloon expulsion, then a transit study, before escalating further.
| Class | Examples | Mechanism | Cautions |
|---|---|---|---|
| Bulk-forming | Psyllium | Holds water, adds bulk | Bloating; may worsen slow transit or dyssynergia |
| Osmotic | PEG 3350, lactulose, magnesium salts | Nonabsorbed solutes draw water into the lumen | Lactulose bloats; magnesium → hypermagnesemia in CKD |
| Stimulant | Senna, bisacodyl | Myenteric plexus stimulation → peristalsis and secretion | Cramping; melanosis coli with senna |
| Secretagogue | Linaclotide, plecanatide; lubiprostone | Guanylate cyclase-C agonist (↑cGMP → CFTR Cl⁻/HCO₃⁻ secretion); ClC-2 channel activator | Diarrhea; nausea with lubiprostone |
| Prokinetic | Prucalopride | Selective 5-HT4 agonist | Headache, diarrhea |
| PAMORA | Methylnaltrexone, naloxegol, naldemedine | Peripheral μ-opioid receptor antagonist | Opioid-induced only; contraindicated in bowel obstruction |
Specific agents. PEG has the best evidence of any laxative. Avoid magnesium salts in advanced CKD; sodium phosphate enemas and oral preparations can cause hyperphosphatemia and acute phosphate nephropathy in CKD, dehydration and older adults. Stimulant laxatives are safe for long-term use. Chronic anthraquinone (senna) use produces melanosis coli—brown mucosa from lipofuscin-laden macrophages in the lamina propria—which is benign and reversible.
Opioid-induced constipation. Opioids bind enteric μ-receptors, slowing transit and reducing secretion, and tolerance to this effect does not develop. Every opioid prescription should come with a scheduled stimulant laxative (senna, plus PEG as needed); docusate alone is ineffective. When laxatives fail, add a peripherally acting μ-opioid receptor antagonist: methylnaltrexone (subcutaneous or oral), naloxegol or naldemedine. These do not cross the blood-brain barrier—methylnaltrexone is a charged quaternary amine—so analgesia is preserved. They are contraindicated with known or suspected mechanical obstruction because of perforation risk.
Refractory constipation: outlet versus colon
Laxative-refractory constipation has three physiologic subtypes: normal-transit (most common, overlapping with IBS-C), dyssynergic defecation, and slow-transit constipation. Test the outlet first, because dyssynergia itself slows transit and can masquerade as colonic inertia.
| Feature | Dyssynergic defecation | Slow transit |
|---|---|---|
| Problem | Puborectalis and external anal sphincter contract paradoxically or fail to relax while straining | Weak colonic propulsion (colonic inertia) |
| Symptoms | Excessive straining, incomplete evacuation, digital maneuvers | Infrequent stools, no urge, bloating |
| Key test | Anorectal manometry + balloon expulsion (cannot expel a 50-mL balloon within 1–2 min) | Radiopaque marker study (>5 of 24 markers on day-5 film) or wireless motility capsule |
| Treatment | Biofeedback (pelvic floor retraining), superior to laxatives | Laxatives, secretagogues, prucalopride; subtotal colectomy with ileorectal anastomosis if severe and refractory |
Fecal impaction and fecal incontinence
Fecal impaction. Older adults who are immobile, cognitively impaired, dehydrated or taking opioids and anticholinergics develop a hard stool mass in the rectum. Liquid stool seeps around it, producing overflow "diarrhea" and soiling, often with anorexia, abdominal pain, urinary retention or delirium. DRE usually confirms it; an abdominal radiograph finds a more proximal impaction. Treat with manual disimpaction, then enemas (tap water or mineral oil), then a daily PEG regimen to prevent recurrence. Untreated impaction can cause stercoral ulceration and perforation.
Loperamide for "diarrhea" in an immobile, constipated older patient worsens impaction—do a rectal exam first.
Fecal incontinence. Common causes include:
- Obstetric anal sphincter injury (third- or fourth-degree tears, forceps), which may surface decades later after menopause
- Pudendal neuropathy from prolonged labor or chronic straining
- Overflow from impaction
- Neurologic disease: spinal cord injury, multiple sclerosis, diabetic neuropathy, dementia
- Diarrhea of any cause, rectal prolapse, anorectal surgery
Evaluation and treatment. DRE assesses resting tone and squeeze; anorectal manometry and endoanal ultrasound define sphincter function and defects. First-line care firms and regularizes stool—fiber (psyllium) for bulk, loperamide to slow transit and raise internal sphincter tone, scheduled toileting—combined with biofeedback and pelvic floor exercises. Overflow incontinence is treated by clearing the impaction, never with antidiarrheals. A discrete sphincter defect that fails conservative care is repaired with overlapping sphincteroplasty; sacral nerve stimulation is an option for refractory cases, and a colostomy is the last resort.