Collagenous colitis

This code represents collagenous colitis, a microscopic inflammatory bowel disease characterized by chronic watery diarrhea. Histologically, it is defined by a thickened subepithelial collagen layer in the colon, along with increased intraepithelial lymphocytes and chronic inflammatory cells in the lamina propria.

Apply this code when documentation explicitly states a diagnosis of collagenous colitis, typically confirmed by colonoscopy with biopsy. This diagnosis is often made in patients presenting with chronic, non-bloody watery diarrhea, particularly in middle-aged or older adults.

• Ensure the pathology report specifically identifies "collagenous colitis" to support this diagnosis.
• Do not confuse with lymphocytic colitis (K52.832), which has similar symptoms but distinct histological findings.
• Code any associated symptoms, such as diarrhea (R19.7), as secondary diagnoses.