Case of diarrhoea

A 66year woman presented to our hospital with a 6week history of watery diarrhoea and central abdominal pain. She was taking naproxen occasionally with omeprazole for osteoarthritis but was not on any other regular medications. She had no significant medical history. On admission, physical examination was unremarkable. Laboratory evaluation showed an elevated C reactive protein of 95 mg/L and white cell count of 11.8×10/L. The remainder of her routine biochemistry was within normal ranges. On admission, faecal pathogen PCR panel for bacterial infection including Clostridioides difficile (C. difficile) was negative. Abdominal Xray showed mild thickening of the left colon. A recent faecal calprotectin that was elevated at 3620 μg/L (normal <50) was noted. A flexible sigmoidoscopy was performed and the appearance was as shown in (figure 1). Biopsies were taken (figure 2). Flexible sigmoidoscopy showed features of colitis with widespread pseudomembranes (a layer resembling a membrane over a mucosal surface) giving the endoscopic impression of C. difficile infection. However, repeated stool cultures were negative. Histology revealed a normal crypt architecture with pseudomembranes erupting from the surface of the mucosa. There was an excess of inflammatory cells in the lamina propria and a thickened subepithelial collagen band in keeping with a diagnosis of pseudomembranous collagenous colitis, a rare subtype of microscopic colitis (MC)/collagenous colitis (figure 2). Colonic pseudomembranes form from fibrinous exudate and acute inflammatory cells on the surface of the mucosa, most commonly driven by infection with C. difficile or ischaemia. However, rarer noninfectious causes have also been described including this variant of MC. Pseudomembranous collagenous colitis is uncommon. To date, there are only 15 case series/reports in the literature, with the largest case series having 10 patients. Typically, MC has a normal mucosal appearance, however, in 20% of patients inflammatory changes have been described. 4 A single case series of 10 patients reports inflammatory changes in all patients in addition to pseudomembranous collagenous colitis. Similar to classic MC, the use of nonsteroidal antiinflammatory drugs (NSAIDs) was also associated with statins, proton pump inhibitors and some antidepressants. This entity responds well to treatment with steroids as well as withdrawal of contributing medications. In our case, the patient was discharged with a 8week course of budesonide MMX 9 mg/day and advised to avoid NSAIDs. At followup 3 months later, her symptoms had resolved and a faecal calprotectin was undetectable (<3.8 μg/L). Giorgio Bartalucci, David Parham, Richard Felwick 1 Gastroenterology, University Hospital Southampton NHS Foundation Trust, Southampton, UK Histopathology, University Hospital Southampton NHS Foundation Trust, Southampton, UK