Constipation occurs in 15% of adults and up to one-third of elderly adults and is a common reason for seeking medical attention. It is more common in women. Older individuals are predisposed due to comorbid medical conditions, medications, poor eating habits, decreased mobility and, in some cases, inability to sit on a toilet (bed-bound patients). The first step in evaluating the patient is to determine what is meant by “constipation.” Patients may define constipation as infrequent stools (fewer than three in a week), hard stools, excessive straining, or a sense of incomplete evacuation.
Most patients have constipation that cannot be attributed to any structural abnormalities or systemic disease. Some of these patients have normal colonic transit time; however, a subset have slow colonic transit or defecatory disorders.
Normal colonic transit time is approximately 35 hours; more than 72 hours is significantly abnormal. Slow colonic transit is commonly idiopathic but may be part of a generalized gastrointestinal dysmotility syndrome. Patients may complain of infrequent bowel movements and abdominal bloating.
Slow transit is more common in women, some of whom have a history of psychosocial problems (depression, anxiety, eating disorder, childhood trauma) or sexual abuse. Normal defecation requires coordination between relaxation of the anal sphincter and pelvic floor musculature while abdominal pressure is increased.
Patients with defecatory disorders (also known dyssynergic defecation)—women more often than men— have impaired relaxation or paradoxical contraction of the anal sphincter and/or pelvic floor muscles during attempted defecation that impedes the bowel movement. This problem may be acquired during childhood or adulthood.
Patients may complain of excessive straining, sense of incomplete evacuation, or need for digital manipulation.
Patients with primary complaints of abdominal pain or bloating with alterations in bowel habits (constipation, or alternating constipation and diarrhea) may have irritable bowel syndrome.
Constipation may be caused by systemic disorders, medications, or obstructing colonic lesions. Systemic disorders can cause constipation because of neurologic gut dysfunction, myopathies, endocrine disorders, or electrolyte abnormalities (eg, hypercalcemia or hypokalemia); medication side effects are often responsible (eg, anticholinergics or opioids).
Colonic lesions that obstruct fecal passage, such as neoplasms and strictures, are an uncommon cause but important in new-onset constipation. Such lesions should be excluded in patients older than age 50 years, in patients with “alarm” symptoms or signs (hematochezia, weight loss, anemia, or positive fecal occult blood tests [FOBT] or fecal immunochemical tests [FIT]), and in patients with a family history of colon cancer or inflammatory bowel disease.
Defecatory difficulties also can be due to a variety of anorectal problems that impede or obstruct flow (perineal descent, rectal prolapse, rectocele), some of which may require surgery, and Hirschsprung disease (usually suggested by lifelong constipation).
Dietary and lifestyle measures: Adverse psychosocial issues should be identified and addressed. Patients should be instructed on normal defecatory function and optimal toileting habits, including regular timing, proper positioning, and abdominal pressure. Adequate dietary fluid and fiber intake should be emphasized.
Increased dietary fiber may cause distention or flatulence, which often diminishes over several days. Response to fiber therapy is not immediate, and increases in dosage should be made gradually over 7–10 days. Fiber is most likely to benefit patients with normal colonic transit, but it may not benefit patients with colonic inertia, defecatory disorders, opioid-induced constipation, or irritable bowel syndrome; it may even exacerbate symptoms in these patients. Regular exercise is associated with a decreased risk of constipation.
Laxatives: Laxatives may be given on an intermittent or chronic basis for constipation that does not respond to dietary and lifestyle changes. There is no evidence that long-term use of these agents is harmful.
Osmotic laxatives: Treatment usually is initiated with regular (daily) use of an osmotic laxative. Nonabsorbable osmotic agents increase secretion of water into the intestinal lumen, thereby softening stools and promoting defecation.
Magnesium hydroxide, nondigestible carbohydrates (sorbitol, lactulose), and polyethylene glycol are all efficacious and safe for treating acute and chronic cases. The dosages are adjusted to achieve soft to semi-liquid movements. Magnesium-containing saline laxatives should not be given to patients with chronic renal insufficiency.
Nondigestible carbohydrates may induce bloating, cramps, and flatulence. Polyethylene glycol 3350 (Miralax) is a component of solutions traditionally used for colonic lavage prior to colonoscopy and does not cause flatulence. When used in conventional doses, the onset of action of these osmotic agents is generally within 24 hours.
For more rapid treatment of acute constipation, purgative laxatives may be used, such as magnesium citrate. Magnesium citrate may cause hypermagnesemia.
Stimulant laxatives: For patients with incomplete response to osmotic agents, stimulant laxatives may be prescribed as needed as a “rescue” agent or on a regular basis three or four times a week. These agents stimulate fluid secretion and colonic contraction, resulting in a bowel movement within 6–12 hours after oral ingestion or 15–60 minutes after rectal administration. Oral agents are usually administered once daily at bedtime. Common preparations include bisacodyl, senna, and cascara.
Chloride secretory agents: Several agents stimulate intestinal chloride secretion either through activation of chloride channels (lubiprostone) or guanylcyclase C (linaclotide and plecanatide), resulting in increased intestinal fluid and accelerated colonic transit.
Opioid-receptor antagonists: Long-term use of opioids can cause constipation by inhibiting peristalsis and increasing intestinal fluid absorption. Methylnaltrexone (450 mg orally once daily), naloxegol (25 mg orally once daily) and naldemedine (0.2 mg orally once daily) are mu-opioid receptor antagonists that block peripheral opioid receptors (including in the gastrointestinal tract) without affecting central analgesia. They are approved for the treatment of opioid-induced constipation in patients receiving opioids for chronic noncancer pain.
Severe impaction of stool in the rectal vault may result in obstruction to further fecal flow, leading to partial or complete large bowel obstruction. Predisposing factors include medications (eg, opioids), severe psychiatric disease, prolonged bed rest, neurogenic disorders of the colon, and spinal cord disorders. Clinical presentation includes decreased appetite, nausea and vomiting, and abdominal pain and distention. There may be paradoxical “diarrhea” as liquid stool leaks around the impacted feces. Firm feces are palpable on digital examination of the rectal vault. Initial treatment is directed at relieving the impaction with enemas (saline, mineral oil, or diatrizoate) or digital disruption of the impacted fecal material.