Collagenous enterocolitis manifesting as watery diarrhoea and iron-deficiency anaemia

A 56-year-old Caucasian woman presented with epigastric pain, watery diarrhoea, bloating and flatulence following treatment with duloxetine and venlafaxine for anxiety and depression. Abdominal examination was benign. Blood work revealed haemoglobin of 96 g/L (115-160 g/L), iron 6 μmol/L (10-33 μmol/L), transferrin saturation 0.08 (0.20-0.55), ferritin 26 μg/L (15-180 μg/L), albumin 46 g/L (35-50 g/L), pre-albumin 293 mg/L (170-370 mg/L), total IgA 2.64 g/L (0.78-3.58 g/L) and anti-tTG IgA 5 units (<20 units). Faecal occult blood tests were 3/3 positive and stool cultures were negative. CT enterography was normal. Colonic biopsy revealed collagenous colitis, while duodenal biopsy showed collagenous sprue with blunted to completely flattened villi and markedly thickened subepithelial collagen table entrapping capillaries and lymphocytes. The patient started a gluten-free diet, loperamide and ferrous gluconate. Her symptoms resolved and a faecal immunochemical test performed 6 months later was negative.