Update your Knowledge with MKSAP 18 Q&A: Answer and Critique


A: Crohn disease

Educational Objective

Diagnose Crohn disease.


The patient has Crohn colitis presenting as a chronic inflammatory diarrhea. Common symptoms are abdominal pain, diarrhea, and weight loss; overt gastrointestinal bleeding is a less common manifestation. Crohn disease has varied presentations that can make diagnosis difficult. The pattern of inflammation and histologic features in this case allow distinction of Crohn disease from other inflammatory conditions. Colonoscopy findings are consistent with Crohn colitis based on patchy distribution of mucosal inflammatory changes with normal intervening mucosa, called “skip areas.” The biopsy results show distorted and branching colonic crypts, which are indicative of chronic colitis. The skip areas of normal intervening mucosa and biopsy results for involved mucosa showing features of chronicity (distorted and branching colonic crypts) make Crohn disease the most likely diagnosis.

The patient is at risk for Giardia lamblia infection because she works in a child care center. However, Giardia is a small-bowel protozoal pathogen and does not cause the symptoms of colonic inflammation with bloody diarrhea. Although most patients with giardiasis are asymptomatic, those with symptoms note abdominal pain and cramping with diarrhea, often consisting of large-volume, watery, and foul-smelling stools. Symptoms may be acute or chronic.

Microscopic colitis does not cause bloody diarrhea but rather is a cause of chronic watery diarrhea predominantly in women, with a peak onset between ages 60 and 70 years. Also, colonoscopy results are normal in patients with this condition, with inflammation only seen on biopsy.

Ulcerative colitis typically presents with bloody diarrhea and abdominal discomfort, the severity of which is related to the extent and severity of inflammation. Because ulcerative colitis typically involves the rectum, tenesmus, urgency, rectal pain, and fecal incontinence are common. Patients with ulcerative colitis have distorted and branching colonic crypts on biopsy, but the distribution of inflammation begins in the rectum and progresses up the colon in a continuous and symmetric pattern, without skip areas.

Key Point

Colonoscopy results in Crohn disease show patchy distribution of mucosal inflammatory changes with “skip areas” of normal intervening mucosa, and biopsy results for involved mucosa show features of chronicity (distorted and branching colonic crypts).


Lee JM, Lee KM. Endoscopic diagnosis and differentiation of inflammatory bowel disease. Clin Endosc. 2016;49:370-5. [PMID: 27484813] doi:10.5946/ce.2016.090

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