Diarrhea can range in severity from an acute self-limited episode to a severe, life-threatening illness. To properly evaluate the complaint, the clinician must determine the patient’s normal bowel pattern and the nature of the current symptoms.
Approximately 10 L/d of fluid enter the duodenum of which all but 1.5 L/d are absorbed by the small intestine. The colon absorbs most of the remaining fluid, with less than 200 mL/d lost in the stool. Although diarrhea sometimes is defined as a stool weight of more than 200–300 g/24 h, quantification of stool weight is necessary only in some patients with chronic diarrhea. In most cases, the physician’s working definition of diarrhea is increased stool frequency (more than three bowel movements per day) or liquidity of feces.
The causes of diarrhea are myriad. In clinical practice, it is helpful to distinguish acute from chronic diarrhea, as the evaluation and treatment are entirely different (Tables 15–5 and 15–6).
++ Table Graphic Jump Location Table 15–5.Causes of acute infectious diarrhea. ||Download (.pdf) Table 15–5. Causes of acute infectious diarrhea.
|Noninflammatory Diarrhea ||Inflammatory Diarrhea |
Noroviruses, astrovirus, adenovirus, rotavirus, sapovirus coronavirus SARS-CoV-2
1. Preformed enterotoxin production
2. Enterotoxin production
Enterotoxigenic Escherichia coli (ETEC)
Vibrio cholera, Vibrio vulnificus
1. Cytotoxin production
Enterohemorrhagic E coli O157:H5 and O157:H7 (EHEC)
2. Mucosal invasion
Enteroinvasive E coli (EIEC)
Table Graphic Jump Location Table 15–6.Causes of chronic diarrhea. ||Download (.pdf) Table 15–6. Causes of chronic diarrhea.
CLUES: Stool volume decreases with fasting; increased stool osmotic gap
Medications: antacids, lactulose, sorbitol
Disaccharidase deficiency: lactose intolerance
Factitious diarrhea: magnesium (antacids, laxatives)
CLUES: Large volume (> 1 L/day); little change with fasting; normal stool osmotic gap
Hormonally mediated: VIPoma, carcinoid, medullary carcinoma of thyroid (calcitonin), Zollinger-Ellison syndrome (gastrin)
Factitious diarrhea (laxative abuse); phenolphthalein, cascara, senna
Bile salt malabsorption (idiopathic, ileal resection; Crohn ileitis; postcholecystectomy)
CLUES: Fever, hematochezia, abdominal pain
Malignancy: lymphoma, adenocarcinoma (with obstruction and pseudodiarrhea)
Common offenders: SSRIs, cholinesterase inhibitors, NSAIDs, proton pump inhibitors, angiotensin II receptor blockers, metformin, allopurinol
CLUES: Weight loss, abnormal laboratory values; fecal fat > 10 g/24 h
Small bowel mucosal disorders: celiac disease, tropical sprue, Whipple disease, eosinophilic gastroenteritis, small bowel resection (short bowel syndrome), Crohn disease
Lymphatic obstruction: lymphoma, carcinoid, infectious (tuberculosis, MAI), Kaposi sarcoma, sarcoidosis, retroperitoneal fibrosis
Pancreatic disease: chronic pancreatitis, pancreatic carcinoma
Bacterial overgrowth: motility disorders (diabetes, vagotomy), scleroderma, fistulas, small intestinal diverticula
CLUES: Systemic disease or prior abdominal surgery
Postsurgical: vagotomy, partial gastrectomy, blind ...