Constipation

See Anorectal Physiology Testing for the diagnostic toolkit referenced below, and Rectocele / Rectal Prolapse (Procidentia) / Solitary Rectal Ulcer Syndrome (SRUS) for anatomic causes of obstructed defecation that overlap with constipation workup. Content below is from a textbook reference chapter (Sabiston Ch52 - Pelvic Floor Disorders & Constipation), not primary literature.

Overview

A frequent condition, affecting more than 50% of the population over 65, though it can present at younger ages in a smaller subset. Several medical conditions can contribute — metabolic, endocrine, neurologic, and psychiatric disorders. In adults, new-onset constipation is always a worrisome symptom and the primary cause must be excluded — hypothyroidism and medication-induced constipation are common causes. The presence of colorectal malignancy and other causes of colonic obstruction must be excluded with colonoscopy.

Initial management

Patients should be counseled to increase fluid intake to 1.5–2 L/day and increase dietary fiber. Polyethylene-glycol-based products (e.g. MiraLAX), probiotics, and over-the-counter products may help. Stimulant laxatives (bisacodyl, senna) should not be used long-term. A locally acting chloride channel activator (lubiprostone; Amitiza), a guanylate cyclase agonist (Linzess), and/or a serotonin 5-HT4 agonist (Motegrity) can all be used to treat symptoms.

Long-term constipation resistant to medical treatment and laxatives should be further investigated.

Rome IV criteria for functional constipation

Functional constipation is diagnosed if (1) there are at least two of the following symptoms, during at least 25% of defecations, for at least 3 months: straining, lumpy or hard stools, a sensation of incomplete evacuation, sensation of anorectal obstruction/blockage, need for manual maneuvers to facilitate defecation (e.g. digital evacuation, support of the pelvic floor), or fewer than three spontaneous bowel movements per week; (2) loose stools rarely present without the use of laxatives; and (3) there are insufficient criteria for irritable bowel syndrome.

In the presence of obstructed defecation symptoms, defecography, anorectal manometry, balloon expulsion testing, and electromyography can exclude the presence of pelvic floor disorders (see Anorectal Physiology Testing). Measuring colonic transit time with radio-opaque markers (Sitzmark) can establish the diagnosis of slow transit constipation (colonic inertia) — which can have a neuropathic origin even without a specific histologic change having been demonstrated.

Slow transit constipation

Bowel movement frequency in these patients varies from 1–2 per week to as infrequent as one per month. Some patients are unable to have a complete bowel movement without laxatives or enemas. Severe constipation is associated with abdominal distension, abdominal pain, and nausea, and these symptoms can significantly impair quality of life. Chronic symptoms can present from childhood or adolescence. Slow transit constipation can present with a megacolon on plain x-ray; water-soluble enema or colon CT can show a redundant, hypotonic colon, and colonoscopy similarly demonstrates a dilated hypotonic colon. In a subset of patients, the colon can appear normal (not dilated) on radiologic exam, making diagnosis and the decision to pursue surgical treatment more challenging.

Surgical treatment is indicated in highly symptomatic patients who failed aggressive medical therapy and whose quality of life is severely impaired:

• Total abdominal colectomy with ileorectal anastomosis (TAC-IRA), or colectomy with ileorectal anastomosis (CIRA) — has demonstrated good clinical improvement with acceptable morbidity, and can be performed with minimally invasive technique. Despite that, reported long-term follow-up shows postoperative diarrhea in 5–15%, abdominal pain in 30–50%, small bowel obstruction in 10–20%, fecal incontinence, and recurrence of constipation in 10–30% — yet most patients report satisfaction with functional results after colectomy and IRA overall.
• Segmental colon resections based on transit-time measurements are no longer recommended.
• A permanent ostomy (usually an ileostomy) is described as the extreme therapeutic solution proposed to patients with intractable constipation.

Open items / gaps

• No primary trial data on the newer constipation medications (lubiprostone, linaclotide, prucalopride) referenced above by brand name.
• No detail on how anismus (paradoxical puborectalis contraction, diagnosed by EMG per Anorectal Physiology Testing) is specifically treated (e.g. biofeedback protocols) — worth a dedicated source.