Differential Diagnosis

 Irritable bowel syndrome (IBS) is a disorder of unknown etiology characterized by cramping abdominal pain and a change in bowel habit  which manifests as either diarrhea IBD-D or constipation IBD-C.  Associated symptoms may include nausea and postprandial bloating.  Women are affected more often than men, and the onset of disease is usually before the age of 35.  Caucasians are affected more often than non-whites, and Jews show a higher prevalence than non-Jews. 

 Empiric therapy for possible underlying lactose intolerance may be initiated based on symptoms.  In patients with intractable diarrhea, following a lactose free diet may improve symptoms.  The hydrogen breath test may be performed if further confirmation is needed or if there is confusion as to the diagnosis. In patients who lack warning signs (guiac positive stools or hematochezia, fever, anemia, or weight loss) the diagnosis may be made clinically when there is a history of abdominal pain associated with altered bowel habits for at least three months duration. Extensive investigation with labs, radiographic studies or endoscopic exams are not necessary in patients less than 50 years at initial presentation who lack warning signs. If celiac disease is a possible etiology, then appropriate serologic studies should be performed.

Therapy should start with an evaluation of possible inciting stressors either dietary or environmental.  Instructing patients to keep a diary is often informative at this stage.  If any such stressors are identified, they should be avoided if possible. Patients should also be instructed to try eating smaller meal volumes and to initiate an exercise program.  If symptoms persist, fiber supplementation may prove beneficial.  If constipation is a predominant symptom, fiber along with copious amounts of water should be prescribed.  Conversely, if diarrhea is the predominant symptom, then fiber should be taken with a minimal amount of water in an effort to increase stool bulk. Polyethylene glycol is an effective next step in patients with IBD-C. For female not male patients with IBD-C luboprostone or tegaserod are other options. For symptom control, serotonin reuptake inhibitors may be helpful. Patients with diarrhea predominant IBS may benefit from loperamide (Imodium) or diphenoxylate with atropine (Lomotil).  If these agents fail a trial of a tricyclic antidepressant at low doses may be effective in controlling both diarrhea and abdominal pain.  If the diarrhea still proves refractory, a trial of verapamil or cholestyramine may provide relief.  Abdominal cramping may respond to therapy with hyoscyamine, donnatal, or dicyclomine given prior to meals.  Rifaximin may prove helpful with contolling bloating.