General Principles in Older Adults
Patients with diarrhea most often complain of frequent stools (>3/day) or loose stools. However, other patients use the term diarrhea to describe fecal incontinence or fecal urgency. The etiology of acute diarrhea (lasting <2 weeks) in older adults is similar to that of younger adults, with a few exceptions. Most cases of acute diarrhea are related to viral or bacterial infections, but it can also be caused by medications, medication interactions, or dietary supplements. Clostridium difficile colitis is more prevalent in older adults because of more frequent hospitalizations, increased antibiotic use, and increased numbers of patients in institutional settings. C. difficile colonization in long-term care facilities has been estimated to be at least 50% in the United States. Chronic diarrhea, lasting longer than 2 weeks, may result from fecal impaction, medications, irritable bowel syndrome, IBD, obstruction from colon cancer, malabsorption, small bowel bacterial overgrowth, thyrotoxicosis, or lymphoma.
Small bowel bacterial overgrowth occurs when small bowel transit is slowed, or when the normal flora of the colon is altered with antibiotic treatment. The phenomenon causes premature fermentation of sugars by bacteria in the small bowel, leading to production of methane and/or hydrogen, which causes bloating and flatulence.
Lactase deficiency is common worldwide and is present in most individuals to some degree as they age, although it is less common in northern Europeans, North American Indians, and certain groups in Africa. Symptoms of bloating, abdominal distention, and loose stools usually begin in early adulthood, often worsening with age. Patients are usually aware that they are lactose intolerant; however, lactose intolerance can develop acutely after an episode of diarrhea because of other causes. This usually resolves, but may take several weeks or months in some patients. Celiac disease is an increasingly recognized cause of diarrhea and bloating in older adults. Whether this is occurring de novo in later life, or reflects chronic gluten intolerance is not clear. Uncommon causes of diarrhea include Whipple disease, jejunal diverticulosis, bowel ischemia, amyloidosis, lymphoma, and scleroderma with bacterial overgrowth.
A complete history and physical examination, including a rectal examination, may provide information on cause and direct further evaluation. Medication history may reveal a causative agent for the diarrhea, and recent antibiotic use or hospitalization should trigger a work-up for C. difficile. A history of recent weight loss raises the concern for malignancy, IBD, microcytic colitis, malabsorption, or thyrotoxicosis. Fluid status should be assessed in all older patients with diarrhea because they are particularly susceptible to dehydration. Characteristic signs of bloating and gas may indicate small bowel overgrowth, or even underlying celiac disease.
Stool cultures should be obtained to exclude infection in patients with acute diarrhea. Routine stool cultures usually give a specific diagnosis in only 20% to 30% of cases, likely because most diarrheas are caused by viruses such as rotavirus and Norwalk agent. C. difficile toxin assay (toxin A and possibly toxin B) should be obtained if there is a history of recent antibiotic use. For chronic diarrhea, qualitative or quantitative stool fat should be checked to detect steatorrhea, and a thyroid-stimulating hormone (TSH) should be performed. In patients with C. difficile who fail sequential therapy with metronidazole first and then oral vancomycin, third line antibiotics such as rifaxamin or fidaxomin can be used. Colonoscopy is appropriate in patients with a history of weight loss, bloody diarrhea, and diarrhea lasting >4 weeks. If the colonoscopy appears grossly normal, biopsies should be obtained to rule out microscopic colitis, which has a much higher prevalence in older adults. The mucosa may look normal, however biopsies demonstrate white cell infiltrates in the submucosa. Colonoscopy has a risk of causing perforation in patients with acute diarrhea caused by colitis, and should be used cautiously in patients with acute IBD or severe colitis. X-rays and CT scan of the abdomen may demonstrate bowel wall thickening with severe enteritis or colitis, and are also useful if complications such as perforation or abscess formation are suspected. In patients who are suspected to have small bowel bacterial overgrowth, a positive breath hydrogen/methane test will confirm early fermentation of ingested sugars in the small bowel. Serum antibodies to tissue transglutaminase (tTG), gliadin, and endomysial antigens are often positive in patients with celiac disease, with immunoglobulin (Ig) A tTG being the most sensitive and specific. The diagnosis is made on demonstration of villous damage and atrophy in small bowel biopsies performed during upper endoscopy.
Treatment of diarrhea is based on the underlying cause. In those with no evidence of acute infection and no blood in the stool, loperamide (≤8/day) is generally effective in treating symptoms. Bismuth subsalicylate, which has bactericidal action, can also be used. C. difficile is usually treated with metronidazole, and vancomycin is used for moderate-severe colitis or very ill patients. Older patients have a response to metronidazole that is less than that of younger patients (85% vs. 95%), and relapse of C. difficile diarrhea is more common in the older patient. Antidiarrhea agents should be avoided in C. difficile colitis because of the risk of precipitating ileus and megacolon. Care must be exercised in older adults with commonly used antimotility products, such as Lomotil, which contain atropine. In microscopic colitis, treatment is generally aimed at slowing colonic transit with the use of loperamide. Other alternatives include bismuth subsalicylate, prednisone, cholestyramine, or the 5-ASA products. Deodorized tincture of opium often improves symptoms in patients who fail to respond to other treatments. If small bowel overgrowth is present, then treatment with bismuth-containing medications may be helpful in mild cases. For severe small bowel overgrowth, treatment with 14–21 days of antibiotics to eradicate the bacteria is needed. A variety of antibiotics have been shown to be effective, including ciprofloxacin, neomycin, and rifaximin. If the underlying cause of slow intestinal transit is not addressed, or is not treatable, then overgrowth is likely to recur. Elimination of gluten is the treatment for celiac disease, and has become easier with the increase in gluten-free foods. Medication review is often helpful in patients with refractory celiac disease, as medications have been shown to be an unsuspected source of gluten. Web-based patient support groups are often a valuable resource for this kind of information.