Chronic diarrhoea, lasting more than 3 or 4 weeks, is a common condition with a wide variety of different possible causes. Estimates suggest 5% of the population have experienced chronic diarrhoea and sought medical advice about it. All gastroenterologists see many patients whose principal complaint is frequent, loose stools, and will be aware of investigations that are needed to diagnose serious conditions such as inflammatory bowel disease (IBD) or colorectal cancer (CRC). Most people who present with chronic diarrhoea will not have these conditions and, if less common disorders are not considered, may be given a diagnosis of diarrhoea-predominant irritable bowel syndrome (IBS-D) or perhaps functional diarrhoea.1 Many different treatments are used for IBS-D and often benefit only a small proportion of patients, leaving many with unmet needs, seeking further investigation, advice and treatment.
Guidelines for the investigation of chronic diarrhoea in adults have recently been updated.2 These guidelines provide recommendations for investigating most patients who have chronic diarrhoea, and reflect the now greater availability of simple tests such as faecal calprotectin, coeliac serology, lower gastrointestinal endoscopy and tests for bile acid diarrhoea (BAD). The criteria for functional gastrointestinal disorders were revised in 2016 (Rome IV), with modifications made to the definitions of the various functional bowel disorders (FBD).1 The revised criteria recognise a continuum between functional diarrhoea and IBS-D, and the usefulness of the Bristol stool form scale (BSFS) types 6 and 7 for defining diarrhoea. Approaches to the clinical evaluation of patients are indicated in those articles,1–2 which provide much of the evidence discussed here, backed up by my clinical experience, highlighting certain mistakes that can be made in the management of chronic diarrhoea.