Passing a stool weight or volume greater than 200g or 200mL per 24hours, and it is a symptom instead of a disease

Fundamental process that causes all diarrheal diseases is incomplete absorption of water from intestinal luminal contents

Condition of altered intestinal water and electrolyte transport

Distinguish from decal incontinence where problem is anal sphincter dysfunction instead of dysregulated intestinal fluid or electrolyte absorption

Distinguish from fecal impaction: patients with chronic constipation may develop fecal impaction from inability to expel a large fecal mass through the anus and rectal distention causes relaxation of internal anal sphincter and there is induction of secretions proximal to obstructing stool, liquid stool then passes around the impaction

Diarrhoea is an adverse effect of nearly all medications, make sure to establish temporal relationship between starting use of drug and onset of diarrhoea. E.g. antacids, nutritional supplements that contain Mg2+, antibiotics, PPIs, SSRIs, NSAIDs

Caffeine may cause increased intestinal fluid secretion by elevating intracellular cAMP levels

Antibiotics alter colonic bacterial flora that may then decrease colonic bacterial fermentation of malabsorbed carbohydrates or lead to Clostridium difficile infection

Mesenteric vasoconstriction agents decrease mesenteric blood flow and causes malabsorption

NSAIDs or mycophenolate mofetil are agents that incite intestinal inflammation, thus causing diarrhoea

Chemotherapy causes intestinal or colonic crypt damage, thus impairing water absorption and resulting in apoptotic enterocolopathy

Acute diarrhoea is straightforward as most commonly caused by infection and is self-limited. Note: stool testing and other studies are indicated in the presence of certain clinical or epidemiological features

Chronic diarrhoea warrants diagnostic evaluation, is less likely to resolve on its own and presents a broad differential diagnosis.

Intentionally self-inflicted disorder, frequently surreptitious laxative ingestion, most commonly in women of higher socioeconomic status and often employed in medical field

Can use colonoscopy to evaluate factitious diarrhoea as pseudo-melanosis coli is potential clue found on colonoscopy (brownish discolouration of colonic mucosa caused by accumulation of lipofuscin pigment in macrophages of lamina propria, occurs with use of anthraquinone laxatives)

Stool osmolality can never be less than that of plasma, so a low osmolality of <290 mOsm/kg can only result from adding a hypotonic solution such as water or urine to the stool

High stool osmolality of >600 mOsm/kg can be due to addition of hypertonic solutions such as tomato juice or blood

Abdominal pain, erosive esophagitis, enlarged gastric folds, duodenal ulcers