Microscopic colitis is the most frequent diagnosis of patients with watery chronic diarrhoea and macroscopically normal colonoscopy in a context of clinical practice

It has been suggested that the diagnostic study of watery chronic diarrhoea of functional characteristics should include a limited number of diagnostic tests, but which and in what order is not well established. Aim: To evaluate the frequency of microscopic colitis (MC) and other diagnosis in patients with watery chronic diarrhoea without organic characteristics in a context of clinical practice to establish the best diagnostic strategy. All patients submitted for a colonoscopy due to watery chronic diarrhoea in the 2015–2016 period were included. Watery chronic diarrhoea was defined as the presence of non-bloody diarrhoea with ≥2 stools/day or at least 3 weekly episodes of ≥3 stools/day, lasting ≥4 weeks. We excluded patients with alternating diarrhoea-constipation and those with auto-limited diarrhoea at the time of colonoscopy. In all of them, standard blood analyses (including RCP and coeliac serology),faecal occult blood and stool parasites were negative. Colonoscopy plus multiple mucosal sampling if normal and a battery of tests to rule out specific entities were performed. Functional diarrhoea was defined when the results of all tests were normal and diarrhoea persisted. The consumption of drugs (SIRE registry, Catsalut, Catalonia), associated autoimmune diseases and smoking were recorded. We evaluated 159 patients, but 21 not finishing the diagnostic workup were excluded. Finally, 138 (58 ± 1.4 years, 77% women) were included. The colonic biopsies were diagnostic of MC in 43 (31%) (16 collagenous colitis, 22 lymphocytic colitis, 5 incomplete MC). In 14 out of 95 remaining patients, diarrhoea was self-limiting. In 39 patients (group 'others'), a specific diagnosis (28%) was achieved resolving the diarrhoea (bile acid diarrhoea, 17; diarrhoea due to sugar malabsorption, 9; metformin diarrhoea, 6; celiac disease/gluten sensitivity, 6; parasitic infection, 1). In 42 (30%) patients, all the tests were normal and were diagnosed with functional diarrhoea. There were no differences between the 3 groups (MC, Others, Functional) for sex, smoking, associated diseases, and consumption of NSAIDs, PPIs, statins, SSRI, β-blockers. There were differences in age (65 ± 2.4; 53 ± 2.5; 55 ± 2.6; p = 0.002), and the mean number of drugs consumed (2.7 ± 0.4; 1.2 ± 0.2; 2.2 ± 0.3; p = 0.012). A specific diagnosis was obtained in 60% of patients with watery chronic diarrhoea suggesting ‘functional characteristics’, being microscopic colitis the most frequent diagnosis. Colonoscopy with multiple colon sampling should be the first diagnostic test in such patients.