A 78-year-old male nursing home resident is brought to the physician because of abdominal pain and discomfort. He has a history of advanced dementia and is only partially able to verbalize his symptoms. He has had intermittent abdominal discomfort for years, with no other related symptoms. He denies diarrhea and rectal bleeding but has not had a bowel movement in approximately 5 days. The patient is largely bed-bound, and only has minimal activity with the help of nurses and physical therapists. Past regular colonoscopies have shown only benign lesions. His other medical problems include dementia, coronary artery disease, hypertension, spinal stenosis, and osteoarthritis of his hips and knees. Abdominal examination does not show tenderness, masses, or hepatosplenomegaly, although fullness is appreciated. The remainder of the examination shows no abnormalities. Polyethylene glycol is administered and produces a bowel movement within 24 hours. The mechanism of action of polyethylene glycol in this patient is most similar to the pathophysiology of which of the following disorders?

Question

A 78-year-old male nursing home resident is brought to the physician because of abdominal pain and discomfort.  He has a history of advanced dementia and is only partially able to verbalize his symptoms.  He has had intermittent abdominal discomfort for years, with no other related symptoms.  He denies diarrhea and rectal bleeding but has not had a bowel movement in approximately 5 days.  The patient is largely bed-bound, and only has minimal activity with the help of nurses and physical therapists.  Past regular colonoscopies have shown only benign lesions.  His other medical problems include dementia, coronary artery disease, hypertension, spinal stenosis, and osteoarthritis of his hips and knees.  Abdominal examination does not show tenderness, masses, or hepatosplenomegaly, although fullness is appreciated.  The remainder of the examination shows no abnormalities.  Polyethylene glycol is administered and produces a bowel movement within 24 hours.  The mechanism of action of polyethylene glycol in this patient is most similar to the pathophysiology of which of the following disorders?

Quizplus · Accepted Answer

Constipation is common in elderly, debilitated patients as well as those on chronic opiate therapy. Because lifestyle changes are not an option in patients such as this one, constipation in this population is commonly treated with osmotic laxatives (e.g., magnesium citrate, polyethylene glycol), stool softeners, and enemas. Osmotic laxatives are nonabsorbable or poorly absorbable substances that attract water into the intestinal lumen, thus distending the intestinal wall and increasing peristalsis. The laxative effect is usually fairly rapid. Magnesium hydroxide (and other magnesium-containing compounds, such as magnesium citrate) is another osmotic laxative that is often used, although its efficacy is questionable and there is not enough evidence to support its widespread use. Lactase deficiency is a disease state characterized by osmotic diarrhea. Inherited or acquired deficiency of the intestinal brush border enzyme lactase (i.e., disaccharidase) causes inability to break down lactose into glucose and galactose. Undigested lactose is a nonabsorbable osmotic substance, and its accumulation in the small intestine leads to an increase in the secretion of water and electrolytes into the intestinal lumen. Lactase deficiency (i.e., lactose intolerance) presents with abdominal pain and distension and watery diarrhea. Abdominal pain and distention result from the metabolism of lactose by normal gut flora through fermentation, which causes the production of gas. The symptoms resolve when milk-containing products are eliminated from the diet. (Choice A) Irritable bowel syndrome is a functional intestinal disorder that presents with diarrhea alternating with constipation, abdominal pain, and distention without organic cause. Fecal water and electrolyte content are normal. (Choice B) Diarrhea in Crohn's disease is of the secretory type, which is characterized by high electrolyte content due to poor absorption and increased losses from the inflamed intestinal mucosa. (Choice D) Diarrhea in carcinoid syndrome is secretory and high in electrolytes. (Choice E) Rectal prolapse is a protrusion of rectal mucosa through the anus associated with pregnancy and constipation; it can also be seen in severe diarrhea. Another important cause of rectal prolapse is cystic fibrosis, particularly in children. Educational objective: Polyethylene glycol is an osmotic laxative. Diarrhea associated with lactase deficiency is also osmotic and occurs due to accumulation of nonabsorbable lactose in the intestinal lumen. Magnesium hydroxide (and other magnesium-containing compounds, such as magnesium citrate) is another osmotic laxative that is often used, although its efficacy is questionable and there is not enough evidence to support its widespread use. __________ References: Approach to fecal incontinence and constipation in older hospitalized patients. (http://www.ncbi.nlm.nih.gov/pubmed/21441765) Review of the treatment options for chronic constipation. (http://www.ncbi.nlm.nih.gov/pubmed/17955081)

A 78-Year-Old Male Nursing Home Resident Is Brought to the Physician