Symptoms to Diagnosis

A case of refractory diarrhea

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A 68-year-old white woman with irritable bowel syndrome has had worsening symptoms of right-sided abdominal pain, excessive bloating, and loose stools. Her bowel movements have increased from one a day to two or three a day. She has not noted any mucus or blood in the stool. She cannot identify any alleviating or aggravating factors, and the pain is not related to eating.

She consumes a normal diet, including meat and dairy. Over-the-counter antidiarrheal medications do not relieve the symptoms. She has had no fevers, chills, or night sweats, and she has not lost weight over the past year.

Her medical history includes breast cancer (in remission), alcohol abuse (in remission), and hypothyroidism, osteoporosis, and supraventricular tachycardia, all controlled with treatment as noted below. She has never undergone abdominal surgery.

A general review of systems is normal. Her current medications include oxybutynin (available as Ditropan, others), calcium polycarbophil (FiberCon, others), risedronate (Actonel), levothyroxine (Synthroid, others), simethicone (Maalox Anti-Gas, others), atenolol (Tenormin), trazodone (Desyrel), a calcium supplement, and aspirin. She began taking duloxetine (Cymbalta) 18 months ago, and the dose was increased from 60 mg to 90 mg 1 week before this visit.

She has never smoked, and she has abstained from alcohol for 10 years. She has no family history of colon cancer, celiac disease, or inflammatory bowel disease. She has not traveled outside the country in the past several years, and she notes no change in her source of drinking water.

On physical examination, she does not appear to be in acute distress. Her pulse is 64 and her blood pressure is 112/78 mm Hg. The cardiopulmonary examination is normal. Her abdomen is soft, symmetrical, nondistended, and nontender. Bowel sounds are normal. No abdominal masses, palpable organomegaly, or abdominal bruits are noted.

Results of basic laboratory tests, including thyroid-stimulating hormone (TSH), complete blood count, blood chemistries, renal function, and liver function, are normal. Colonoscopy shows normal mucosa as far as the cecum.

DIFFERENTIAL DIAGNOSIS

1. In addition to irritable bowel syndrome, which of these can explain her symptoms?

  • Ulcerative colitis
  • Celiac disease
  • Microscopic colitis
  • Hyperthyroidism
  • Lactase deficiency

Ulcerative colitis typically presents with blood and mucus in the stool and gross abnormalities on colonoscopy, none of which is present in this patient.

Hyperthyroidism can be ruled out by the normal TSH level.

Lactase deficiency or lactose intolerance is unlikely because it is present in only 15% of people of northern European descent (compared with 80% of blacks and Hispanics and up to 100% of Native Americans and Asians). 1 Furthermore, her pain is apparently not related to consuming dairy products.

The hydrogen breath test can aid in the diagnosis of lactase deficiency. This test relies on the breakdown of malabsorbed lactose by colonic flora. This is the most widely used test for this deficiency, but its high false-negative rate of 25% means that a negative result does not exclude the diagnosis and should not be relied on in working up a patient with chronic diarrhea. 2 Simply noting whether symptoms develop after ingesting 50 g of lactose is clinically useful when lactase deficiency is suspected.

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