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Difficulty: MediumPathology and Biopsy Interpretation

A 66-year-old woman presents to the clinic with a 3-month history of frequent, watery, nonbloody diarrhea. She reports 5 to 7 loose bowel movements per day, sometimes awakening her at night. She has a medical history of osteoarthritis and depression, for which she takes celecoxib and sertraline. Vital signs are within normal limits, and physical examination of the abdomen is unremarkable. Laboratory tests, including a complete blood count, comprehensive metabolic panel, and thyroid-stimulating hormone, are normal. Stool studies are negative for ova and parasites, and a stool culture yields normal flora. A colonoscopy is performed, which reveals a structurally intact, normal-appearing mucosal surface from the rectum to the cecum. Random colonic biopsies are obtained. Histologic examination demonstrates a thickened, subepithelial, eosinophilic, acellular band measuring 20 micrometers in depth. The surface epithelium is intact but infiltrated by an increased number of intraepithelial lymphocytes. The crypt architecture is completely normal, with no evidence of cryptitis or crypt abscesses. Based on the clinical presentation and histopathologic findings, which of the following is the most likely diagnosis?

  1. A
    Lymphocytic colitis
  2. B
    Crohn disease
  3. Collagenous colitisAnswer
  4. D
    Intestinal amyloidosis
  5. E
    Eosinophilic gastroenteritis

Answer

Collagenous colitis
The patient's presentation of chronic, watery, nonbloody diarrhea with a macroscopically normal colonoscopy and microscopic evidence of a thickened subepithelial eosinophilic band is characteristic of collagenous colitis. This condition is a subtype of microscopic colitis most commonly seen in older women and is often associated with the use of NSAIDs (e.g., celecoxib), proton pump inhibitors, or SSRIs (e.g., sertraline). The definitive diagnosis relies entirely on the histopathologic finding of an acellular collagen band typically greater than 10 micrometers in depth, situated directly beneath the surface epithelium, accompanied by increased intraepithelial lymphocytes and normal, parallel crypt architecture.

Step-by-Step Solution

1
Identify the patient's primary clinical syndrome.
Chronic, watery, nonbloody diarrhea in an older female with a macroscopically normal colon on endoscopy.
This specific clinical presentation strongly suggests microscopic colitis, which necessitates the histopathologic examination of random colonic biopsies to establish a diagnosis.
2
Analyze the histopathologic biopsy findings provided in the stem.
The biopsy demonstrates a thickened subepithelial eosinophilic band (20 micrometers) and increased intraepithelial lymphocytes, while preserving normal crypt architecture.
The subepithelial collagen band is the pathognomonic feature used to differentiate the specific subtypes of microscopic colitis.
3
Synthesize the clinical and pathologic data to formulate the correct diagnosis.
The combination of watery diarrhea, normal gross endoscopy, and a prominent subepithelial collagen band confirms the diagnosis.
These findings are strictly specific for collagenous colitis, definitively distinguishing it from lymphocytic colitis and other etiologies of chronic diarrhea.

Key Concept

The diagnosis of collagenous colitis relies on a clinical history of chronic watery diarrhea, a macroscopically normal colon on endoscopy, and colonic biopsies demonstrating a characteristic thickened subepithelial collagen band with increased intraepithelial lymphocytes.
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Topics

Pathology and Biopsy Interpretation

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