Curriculum · Gastroenterology
Differentiating inflammatory from non-inflammatory diarrhoea
How it presents
The table sets a viral cause against a bacterial one. A viral cause involves the small intestine and gives watery diarrhea with a lot of vomiting, while abdominal pain and cramps, tenesmus, anorexia, fever and systemic illness are mild or not there at all. A bacterial cause involves the colon and gives bloody, mucoid diarrhea; vomiting is much less, and abdominal pain and cramps, tenesmus, anorexia, fever and systemic illness are the marked findings. In a child, fever and abdominal pain with non mucus diarrhea point to viral gastroenteritis.
How it is diagnosed
Fecal leukocytes can be there or not with a viral cause, and are more often there with a bacterial one, so their absence does not close the question. Alongside the stool itself, the history is asked for epidemiological clues that might favor a particular etiology, such as travel or antibiotic use. When the diarrhea is chronic rather than acute the list is grouped along a different line. In an immunocompetent adult in a developed country an infectious cause is uncommon, Giardia lamblia excepted, so the question is which other condition is at work. Microscopic colitis is common, especially in older women, and is easily missed. Small intestinal bacterial overgrowth is increasingly recognized and frequently over-tested and treated. Bile acid malabsorption is a common but underdiagnosed cause of chronic watery diarrhea, particularly after cholecystectomy or with ileal disease. Colonoscopy is advised for most patients with chronic diarrhea, and steatorrhea points the work toward small-bowel malabsorption such as celiac disease, bacterial overgrowth and pancreatic insufficiency. The stool pattern separates the two kinds: osmotic diarrhea comes with eating, improves with fasting and is typically not nocturnal, while secretory diarrhea is large in volume, watery and nocturnal and is unchanged by fasting. Lactase deficiency is the commonest cause of the osmotic kind.