Diarrhea and constipation

Constipation: Treatment After the cause of constipation is characterized, a treatment decision can be made. Slow-transit constipation requires aggressive medical or surgical treatment; anismus or pelvic floor dysfunction usually responds to biofeedback management (Fig. 40-4). However, only ~60% of patients with severe constipation are found to have such a physiologic disorder (half with colonic transit delay and half with evacuation disorder).

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Approach to the Patient: Constipation A careful history should explore the patient's symptoms and confirm whether he or she is indeed constipated based on frequency (e.g., fewer than three bowel movements per week), consistency (lumpy/hard), excessive straining, prolonged defecation time, or need to support the perineum or digitate the anorectum. In the vast majority of cases (probably 90%), there is no underlying cause (e.g., cancer, depression, or hypothyroidism), and constipation responds to ample hydration, exercise, and supplementation of dietary fiber (15–25 g/d).

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ANORECTAL AND PELVIC FLOOR TESTS Pelvic floor dysfunction is suggested by the inability to evacuate the rectum, a feeling of persistent rectal fullness, rectal pain, the need to extract stool from the rectum digitally, application of pressure on the posterior wall of the vagina, support of the perineum during straining, and excessive straining. These significant symptoms should be contrasted with the sense of incomplete rectal evacuation, which is common in IBS.

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A therapeutic trial is often appropriate, definitive, and highly cost effective when a specific diagnosis is suggested on the initial physician encounter.

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CONSTIPATION Definition Constipation is a common complaint in clinical practice and usually refers to persistent, difficult, infrequent, or seemingly incomplete defecation. Because of the wide range of normal bowel habits, constipation is difficult to define precisely. Most persons have at least three bowel movements per week; however, low stool frequency alone is not the sole criterion for the diagnosis of constipation.

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FACTITIAL CAUSES Factitial diarrhea accounts for up to 15% of unexplained diarrheas referred to tertiary care centers. Either as a form of Munchausen syndrome (deception or self-injury for secondary gain) or eating disorders, some patients covertly selfadminister laxatives alone or in combination with other medications (e.g., diuretics) or surreptitiously add water or urine to stool sent for analysis. Such patients are typically women, often with histories of psychiatric illness and disproportionately from careers in health care.

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Postmucosal Lymphatic Obstruction The pathophysiology of this condition, which is due to the rare congenital intestinal lymphangiectasia or to acquired lymphatic obstruction secondary to trauma, tumor, or infection, leads to the unique constellation of fat malabsorption with enteric losses of protein (often causing edema) and lymphocytopenia. Carbohydrate and amino acid absorption are preserved. INFLAMMATORY CAUSES Inflammatory diarrheas are generally accompanied by pain, fever, bleeding, or other manifestations of inflammation.

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OSMOTIC CAUSES Osmotic diarrhea occurs when ingested, poorly absorbable, osmotically active solutes draw enough fluid into the lumen to exceed the reabsorptive capacity of the colon. Fecal water output increases in proportion to such a solute load. Osmotic diarrhea characteristically ceases with fasting or with discontinuation of the causative agent.

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OTHER CAUSES Side effects from medications are probably the most common noninfectious cause of acute diarrhea, and etiology may be suggested by a temporal association between use and symptom onset. Although innumerable medications may produce diarrhea, some of the more frequently incriminated include antibiotics, cardiac antidysrhythmics, antihypertensives, nonsteroidal anti-inflammatory drugs (NSAIDs), certain antidepressants, chemotherapeutic agents, bronchodilators, antacids, and laxatives.

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SECRETORY CAUSES Secretory diarrheas are due to derangements in fluid and electrolyte transport across the enterocolonic mucosa. They are characterized clinically by watery, large-volume fecal outputs that are typically painless and persist with fasting. Because there is no malabsorbed solute, stool osmolality is accounted for by normal endogenous electrolytes with no fecal osmotic gap. Medications Side effects from regular ingestion of drugs and toxins are the most common secretory causes of chronic diarrhea.

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Acute Diarrhea More than 90% of cases of acute diarrhea are caused by infectious agents; these cases are often accompanied by vomiting, fever, and abdominal pain. The remaining 10% or so are caused by medications, toxic ingestions, ischemia, and other conditions. INFECTIOUS AGENTS Most infectious diarrheas are acquired by fecal-oral transmission or, more commonly, via ingestion of food or water contaminated with pathogens from human or animal feces.

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Neural Control The small intestine and colon have intrinsic and extrinsic innervation. The intrinsic innervation, also called the enteric nervous system, comprises myenteric, submucosal, and mucosal neuronal layers. The function of these layers is modulated by interneurons through the actions of neurotransmitter amines or peptides, including acetylcholine, vasoactive intestinal peptide (VIP), opioids, norepinephrine, serotonin, ATP, and nitric oxide. The myenteric plexus regulates smooth-muscle function, and the submucosal plexus affects secretion, absorption, and mucosal blood flow.

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ACUTE DIARRHEA: TREATMENT Fluid and electrolyte replacement are of central importance to all forms of acute diarrhea. Fluid replacement alone may suffice for mild cases. Oral sugarelectrolyte solutions (sport drinks or designed formulations) should be instituted promptly with severe diarrhea to limit dehydration, which is the major cause of death. Profoundly dehydrated patients, especially infants and the elderly, require IV rehydration.

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Table 40-2 Association between Pathobiology of Causative Agents and Clinical Features in Acute Infectious Diarrhea Pathobiolo gy/Agents bation Incu miting Vo Abd ominal Pain ever F rrhea Dia Period Toxin producers Preforme d toxin Bacillus cereus, Staphylococcus aureus, h 1–8 4+ 3– 1–2+ –1+ 0 4+, watery 3– Clostridi um perfringens h 8–24 Enterotox in Vibrio cholerae, enterotoxigenic Escherichia coli, Klebsiella pneumoniae, Aeromonas h 8–72 4+ 2– 1–2+ –1+ 0 4+, watery 3– species Enteroadhe rent Enteropat hogenic and d 1–8 1+ 0– 1–3+ –2+ 0 2+, 1– enteroadh...

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Colonic Motility and Tone The small intestinal MMC only rarely continues into the colon. However, short duration or phasic contractions mix colonic contents, and high-amplitude (75 mmHg) propagated contractions (HAPCs) are sometimes associated with mass movements through the colon and normally occur approximately five times per day, usually on awakening in the morning and postprandially. Increased frequency of HAPCs may result in diarrhea or urgency. The predominant phasic contractions in the colon are irregular and nonpropagated and serve a "mixing" function. ...

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Harrison's Internal Medicine Chapter 40. Diarrhea and Constipation DIARRHEA AND CONSTIPATION: INTRODUCTION Diarrhea and constipation are exceedingly common and together exact an enormous toll in terms of mortality, morbidity, social inconvenience, loss of work productivity, and consumption of medical resources. Worldwide, 1 billion individuals suffer one or more episodes of acute diarrhea each year.

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