Overcoming Diagnostic Anchoring: Refractory Collagenous Colitis Masking Resectable Pancreatic Adenocarcinoma

Abstract

Presentation
We report an 80-year-old female with refractory Collagenous Colitis (CC) presenting with progressive weight loss and altered bowel habits over two years. Her symptoms were initially attributed to CC, creating a diagnostic anchor.

Diagnosis
Initial endoscopy and CT scan (January 2024) were inconclusive. Persistent constitutional symptoms prompted a repeat CT (September 2025), revealing a suspicious pancreatic head mass. Endoscopic Ultrasound (EUS) with fine needle biopsy (FNB) confirmed invasive ductal adenocarcinoma.

Treatment
A staging PET-CT scan confirmed localised disease. Following regional MDM review, the patient (ECOG status 1) was deemed fit for potentially curative-intent surgery (Whipple Procedure). However, she is currently reluctant to undergo the operation and has been provided time to consider her options.

Discussion
This case highlights anchoring bias. In established microscopic colitis, the development of persistent weight loss, new abdominal pain, or lack of response to standard therapy should prompt reconsideration of the diagnosis and early cross-sectional imaging.