1. Chronic Diarrhea: Approach to the Patient
diagnostic evaluation must be rationally directed by a careful history and physical examination
history, physical examination, and routine blood studies
characterize the mechanism of diarrhea
identify diagnostically helpful associations
assess the patient's fluid/electrolyte and nutritional status
onset, duration, pattern, aggravating (especially diet) and relieving factors, and stool characteristics of the diarrhea
note presence or absence of fecal incontinence, fever, weight loss, pain, certain exposures (travel, medications, contacts with diarrhea), and common extraintestinal manifestations (skin changes, arthralgias, oral aphthous ulcers)
The laboratory tools available to evaluate the very common problem of chronic diarrhea are extensive, and many are costly and invasive. As such, the diagnostic evaluation must be rationally directed by a careful history and physical examination (Fig. 40-3A). When this strategy is unrevealing, simple triage tests are often warranted to direct the choice of more complex investigations (Fig. 40-3B). The history, physical examination (Table 40-4), and routine blood studies should attempt to characterize the mechanism of diarrhea, identify diagnostically helpful associations, and assess the patient's fluid/electrolyte and nutritional status. Patients should be questioned about the onset, duration, pattern, aggravating (especially diet) and relieving factors, and stool characteristics of their diarrhea. The presence or absence of fecal incontinence, fever, weight loss, pain, certain exposures (travel, medications, contacts with diarrhea), and common extraintestinal manifestations (skin changes, arthralgias, oral aphthous ulcers) should be noted.

2. Chronic Diarrhea: Approach to the Patient
family history of IBD or sprue
physical findings may offer clues such as a thyroid mass, wheezing, heart murmurs, edema, hepatomegaly, abdominal masses, lymphadenopathy, mucocutaneous abnormalities, perianal fistulae, or anal sphincter laxity
peripheral blood
leukocytosis, elevated sedimentation rate, or C-reactive protein suggests inflammation
anemia reflects blood loss or nutritional deficiencies
eosinophilia may occur with parasitoses, neoplasia, collagen-vascular disease, allergy, or eosinophilic gastroenteritis
blood chemistries may demonstrate electrolyte, hepatic, or other metabolic disturbances
measuring tissue transglutaminase antibodies may help detect celiac disease
A family history of IBD or sprue may indicate those possibilities. Physical findings may offer clues such as a thyroid mass, wheezing, heart murmurs, edema, hepatomegaly, abdominal masses, lymphadenopathy, mucocutaneous abnormalities, perianal fistulae, or anal sphincter laxity. Peripheral blood leukocytosis, elevated sedimentation rate, or C-reactive protein suggests inflammation; anemia reflects blood loss or nutritional deficiencies; or eosinophilia may occur with parasitoses, neoplasia, collagen-vascular disease, allergy, or eosinophilic gastroenteritis. Blood chemistries may demonstrate electrolyte, hepatic, or other metabolic disturbances. Measuring tissue transglutaminase antibodies may help detect celiac disease.

3. INITIAL MANAGEMENT BASED ON ACCOMPANYING SYMPTOMS OR FEATURES
Chronic Diarrhea
Exclude iatrogenic problem: medication, surgery
Blood
p.r.
Colonoscopy + biopsy
Features
e.g., stool, suggest malabsorption
Small bowel: imaging, biopsy, aspirate
Pain aggravated before bm, relieved with bm, sense incomplete evacuation
Suspect IBS
Limited screen for organic disease
No blood, features of malabsorption
Consider functional diarrhea
Dietary exclusion,
e.g., lactose, sorbitol

4. EVALUATION BASED ON FINDINGS FROM A LIMITED AGE APPROPRIATE SCREEN FOR ORGANIC DISEASE
Chronic Diarrhea
Limited screen for organic disease
Low Hb, Alb
Abnormal MCV, MCH
Excess fat in stool
Colonoscopy + biopsy
Small bowel: imaging, biopsy, aspirate
Stool fat >20g/day
Pancreatic function
Normal and stool fat <14g/day
Full gut transit
Titrate Rx to speed of transit
Low K+
Stool volume, OSM, pH
Laxative screen
Hormonal screen
Screening tests all normal
Opioid Rx + follow-up
Persistent chronic diarrhea

5. Chronic Diarrhea

6. Chronic Diarrhea
Diarrhea lasting > 4 weeks

7. Major Causes of Diarrhea According to Predominant Physiologic Mechanism
Chronic Diarrhea
Secretory
Inflammatory
Dysmotility
Osmotic
Steatorrheal
Factitial

8. Secretory Causes of Diarrhea
Due to derangements in fluid and electrolyte transport across the enterocolonic mucosa.
Characterized by a watery, large volume fecal outputs that are typically painless and persist with fasting.
No fecal osmotic gap.

9. Secretory Causes of Diarrhea
Hormones
Medications
Metastatic GI carcinoid tumors
Primary bronchial carcinoids
Gastrinoma
Pancreatic cholera
VIPoma
Medullary carcinoma of the thyroid
Systemic mastocytosis
Colorectal villous adenoma
Stimulant laxatives
Chronic ethanol consumption
Environmental toxins

10. Secretory Causes of Diarrhea
Bowel Resection, Mucosal Disease, Enterocolic Fistula
Congenital Defects in Ion Absorption
Congenital chloridorrhea
Addison’s Disease

11. Osmotic Causes of Diarrhea
When ingested, poorly absorbable, osmotically active solutes draw enough fluid into the lumen to exceed the resorptive capacity of the colon
fecal water output increases in proportion to such solute load
Ceases with fasting or with discontinuation of the causative agent

12. Osmotic Causes of Diarrhea
Osmotic laxatives
Carbohydrate Malabsorption
Magnesium containing antacids
Health supplements
laxatives
Acquired or congenital defects in brush border disaccharidases and other enzymes
Lactase deficiency

13. Steatorrheal Causes of Diarrhea
Increased in fecal output is caused by the osmotic effects of fatty acids, especially after bacterial hydroxylation and to a lesser extent by a neutral fat
Quantitatively: stool fat>7g/d
Rapid transit diarrhea may result in fecal fat up to 14g/d
Daily fecal fat averages
15-25g with SI diseases
>32 g with pancreatic exocrine insufficiency

14. Steatorrheal Causes of Diarrhea
Intraluminal Maldigestion
Mucosal Maldigestion
Chronic pancreatitis
Cystic fibrosis
Pancreatic duct obstruction
somatostatinoma
Celiac disease
Tropical sprue
Whipple’s disease
Mycobacterium avium intracellulare infection in AIDS patient
Abetalipoprotenemia
Giardia infection
Colchicine, cholestyramine, neomycin
Chronic schemia

15. Steatorrheal Causes of Diarrhea
Postmucosal Lymphatic Obstruction
Congenital intestinal lymphangiectasia
Acquired lymphatic obstruction secondary to trauma, tumor, or infection

16. Inflammatory Causes of Diarrhea
Accompanied by pain, fever, bleeding and other manifestation of inflammation
Mechanism of diarrhea may be due to exudation, fat malabsorption, disrupted fluid/electrolyte absorption, hypersecretion or hypermotility from release of inflammatory mediators
Stool analysis: leukocytes or leukocyte derived protein (calprotectin)

17. Inflammatory Causes of Diarrhea
with severe inflammation, exudative protein loss can lead to anasarca
middle aged or older person with chronic inflammatory type diarrhea, especially with blood, should be carefully evaluated to exclude colorectal tumor

18. Inflammatory Causes of Diarrhea
Idiopathic Inflammatory Bowel Disease
Primary or Secondary Forms of Immunodefeciency
Crohn’s disease
Chronic ulcerative colitis
Microscopic colitis
hypogammaglobulinemia

19. Inflammatory Causes of Diarrhea
Eosinophilic Gastroenteritis
Other causes
Hypersensitivity to certain food
Radiation enterocolitis
Chronic graft vs host disease
Behcet’s syndrome
Cronkite-Canada Syndrome

20. Dysmotility Causes of Diarrhea
Rapid transit time may accompany many diarrheas as a secondary or contributing phenomenon, but primary dysmotility is an unusual etiology
Stool features often suggest a secretory diarrhea, but mild steatorrhea of up to 14 g/d can be produced by maldigestion from rapid transit alone

21. Factitial Causes Accounts for up to 15% unexplained diarrheas
Munchausen syndrome( deception or self injury) or eating disorders (self administer laxatives alone or in combination with other medication(diuretics)
Women with histories of psychiatric illness and disproportionately from careers in health care
Hypotension and hypokalemia

22. Dysmotility Causes of Diarrhea
Hyperthyroidism, carcinoid syndrome, certain drugs( PG and prokinetic drugs) may produce hypermotility with diarrhea
Primary visceral neuropathies or idiopathic acquired intestinal obstruction
Diabetic diarrhea
Irritable bowel syndrome