Blog

Introduction

Definition

In patients presenting with diarrhea it is important to distinguish: 

• “true diarrhea,” i. e., too frequent, too fluid, too much volume (over 250−300 g/day) 
• “false diarrhea,” i. e., too frequent, too fluid, but without an increase in stool volume, often caused by fecal impaction in the distal colon (either due to anorectal dysfunction or colorectal stenosis), secondary dissolution and passage of liquid stool 
• increased frequency of essentially normal, formed stool (e. g., irritable bowel syndrome, proctitis).

All three problems may be referred to as “diarrhea” by patients. Targeted clinical questioning is required to differentiate these conditions because “false diarrhea” suggests acute constipation as the underlying cause and requires specific management.

Similarly, the final group represents either functional variation within the normal physiological range, or indicates the presence of distal colorectal disease. Finally, diarrhea must be distinguished from fecal incontinence (uncontrolled evacuation of rectal contents), a common and often unrecognized problem.

Pathophysiology

The distinction between acute and chronic diarrhea is established in clinical practice and serves as the basis for the following summary. The causes of diarrhea can be further divided into five groups on the basis of pathophysiology, although in many cases several pathological processes can be operating simultaneously.

Location of Disease

Diarrhea can also be categorized on the basis of which part of the gastrointestinal tract is affected. Diarrhea is a common symptom of colonic disease that, if persistent, is usually simple to diagnose by endoscopy, e. g., ulcerative colitis, Crohn disease, carcinoma.

The assessment and classification of diarrhea caused by small bowel disease is more difficult. Small bowel diarrhea can occur either due to increased passage of ileal effluent (most commonly secretory diarrhea) or the presence of osmotically active substances in the stool such as excess bile acid, laxatives, or undigested nutrients (e. g., lactose, free fatty acid; osmotic diarrhea). In both cases diarrhea occurs only if the ability of the colon to absorb water and form stool is exceeded.

Duration of Disease

In clinical practice physicians make the distinction between acute (days to weeks) and chronic or chronic, recurrent (more than three weeks) diarrhea, although the three-week cut-off is arbitrary.

Acute Diarrhea

General Considerations on Practical Management

Symptomatic Therapy

There are many different causes of acute diarrheal illness and infective, parasitic, toxic, allergic, and iatrogenic causes must be considered. Acute diarrhea is common, but generally mild and self-limiting. An important question to consider in the management of acute diarrhea is whether immediate investigation is required, or alternatively empirical, symptomatic treatment followed by investigation if the condition does not respond. This decision is based on the severity, type, and duration of symptoms, as well as the general condition of the patient.

Primary Investigation

Immediate investigation is only required for acute diarrhea in exceptional circumstances:

• bloody stool
• severe systemic upset, most commonly high fever, dehydration, collapse
• high-volume diarrhea
• severe underlying disease
• recent travel in the Tropics
• employment in the catering industry
• epidemic diarrheal illness
• infants and young children
• recent antibiotic therapy (see below).

---

Infectious and Parasitic Diarrheal Disease

Classification

Acute diarrhea caused by infective agents is divided into two groups:

• noninflammatory causes (e. g., mediated by toxins), “choleric”
• inflammatory causes (e. g., mediated by invasive infection), “dysentery”.

Noninflammatory Causes

The small bowel is most commonly affected. Typical signs of noninflammatory acute diarrheal disease include high volume, watery diarrhea that can rapidly lead to hypotension, acidosis, and shock, usually without causing a fever.

Important causes include Vibrio cholera, enterotoxigenic E. coli (ETEC), Rotavirus, and Norwalk virus. Giardia and Cryptosporidium are common parasitic causes and produce a similar, although less acute, presentation of the disease. This form of diarrheal disease is mediated by enterotoxins and leukocytes in the stool are not observed.

Inflammatory Causes

The colon is most commonly affected. Inflammatory causes of acute diarrheal disease generally produce smaller volumes of stool than toxic diarrheal disease. The stool is often bloody and purulent containing large numbers of leukocytes. Abdominal pain and high fevers often accompany the diarrheal illness.

Common causes include Shigella species, Campylobacter jejuni, Salmonella, enteroinvasive E. coli (EIEC), and Clostridium difficile (usually after antibiotic therapy as an inpatient). Entamoeba histolytica must be considered in patients returning from the Tropics. Diarrhea associated with fever, arthritis, and erythema nodosum is typical for Yersinia enterocolitica infection.

Food Poisoning

Acute vomiting and diarrhea in a group that shared food, often within six hours of ingestion, strongly suggests food poisoning caused by food contaminated by toxin-producing bacteria (e. g., Staphylococcus aureus, Clostridium perfringens, Bacillus cereus).

Investigation

The infective agent can be identified in only 40−60% of patients with infectious diarrhea. In Europe the average incidence of acute, infectious diarrheal disease includes 14% Salmonella, 14% Campylobacter, 4.3% Clostridium difficile, 3.4% Rota virus, 2.5% Shigella, and 2.5% parasitic. However, marked regional differences exist, and in patients returning from the Tropics and in immunocompromised patients (including AIDS) the prevalence of pathogenic protozoal infection is much higher. A summary of parasitic infections that can be associated with diarrhea is provided in image below.

---

Antibiotic-Associated Diarrhea (Pseudomembranous Colitis)

Between 5−25% of patients treated with broad spectrum antibiotics develop a diarrheal illness two to 20 days after starting therapy. The most common infectious cause of antibiotic-associated diarrhea are the toxins (A and B) produced by Clostridium difficile, a bacterium that proliferates when normal gut flora are suppressed.

The severity of the clinical illness and its duration is very variable; severe disease with fatal outcome can occur. The endoscopic findings (80% in the left hemicolon) vary between diffuse mucosal erythema and severe ulcerative disease with pseudomembrane formation. The diagnosis is confirmed by the detection of C. difficile toxin in the stool.

---

Diarrhea Caused by Toxins

Diarrhea can be caused by endogenous and exogenous toxins.

Endogenous Toxins

Uremia is the most common endogenous toxic cause of diarrhea. This is an important mechanism contributing to diarrhea, which is commonly seen in severe infection and other systemic diseases.

Exogenous Toxins

Arsenic and mercury are exogenous toxins that cause severe diarrhea. If the possibility of arsenic intoxication is raised, the diagnosis can be established by chemical analysis of the arsenic content in the hair and nails. In acute poisoning the green color and garlic odor of the vomitus and diarrhea suggest the diagnosis.

Mercury intoxication most commonly presents acutely with large volume, frequently bloody diarrhea, stained black by the presence of mercury salts (e. g., HgS). Only oral ingestion of mercury salts causes disease; in contrast to the inhalation of mercury vapor, the presence of metallic mercury in the gastrointestinal tract is harmless.

Fungal Poisoning

Mushroom or toadstool poisoning should be considered in patients presenting with acute vomiting and diarrhea. If the symptoms present within three hours of ingestion, this is usually a (generally mild) food poisoning caused by rotten fungi, or rarely trehalose intolerance (a complex carbohydrate found in fungi).

Life-threatening poisoning by Amanita phalloides occurs six to 10 hours after ingestion with vomiting, abdominal colic, and diarrhea often followed by a brief symptomatic recovery before an acute, usually fatal, liver failure supervenes.

Medications

Many drugs can cause diarrhea (e. g., iron preparations, magnesium-containing antacids, colchicine, chemotherapeutic agents, biguanide hypoglycemics).

The possibility of covert laxative use must always be considered. Paradoxically, laxatives are a frequent cause of diarrhea in individuals seeking medical attention for diarrhea. Patients may also create factitious diarrhea by the addition of water or urine to the stool.

Food Allergy

Similar to other organs, the bowel can be affected by allergic reactions. However, this is an uncommon cause of diarrhea. Diarrhea of sudden onset and brief duration, shortly after exposure to a particular foodstuff is typical (e. g., shellfish, eggs, strawberries); with recurrent episodes of gastrointestinal symptoms after repeated exposure. Allergic phenomena affecting other organs are frequent, most commonly the skin (e. g., angioedema, urticaria).

Diagnosis is based on a suggestive clinical history and resolution of symptoms with an exclusion diet sometimes confirmed by trial exposure and skin tests. An allergic etiology for eosinophilic gastroenteritis has been proposed. Abdominal pain, followed by bloody diarrhea, may also occur as a gastrointestinal manifestation of Henoch−Schönlein purpura.

Chronic Diarrhea

General Considerations

Chronic diarrhea (lasting more than 3 weeks) is rarely caused by infectious disease.

Chronic diarrhea is a common symptom with many potential underlying causes.

In general, a focused clinical history provides an initial assessment and provisional segregation of patients with functional (common) and organic (relatively rare) disorders.

Chronic diarrhea that occurs at night, as well as during the day, and is associated withweight loss or rectal bleeding always requires urgent investigation to exclude organic disease.

Functional diarrhea is likely in patients 40 years old with a long history of symptoms, in good general and nutritional health. The provisional diagnosis is supported if colonoscopy and laboratory tests (full blood count, renal and liver biochemistry, inflammatory indices, stool microscopy) are normal.

Chronic Diarrhea with Abnormal Findings on Endoscopy

Ulcerative Colitis

Clinical Features

The first presentation of ulcerative colitis can be difficult to distinguish from infectious gastroenteritis (e. g., Campylobacter jejuni, Salmonella species, Clostridium difficile), because both can present with bloody, mucopurulent diarrhea with intermittent fevers. Repeated stool microscopy and culture for pathogenic organisms and parasites is required. At later stages the diagnosis becomes less difficult.

The disease often “begins” at a relatively young age, between 15 and 50 years, and there is a slight predisposition in women. The diarrhea is usually painless, although anorectal inflammation may cause tenesmus. Rectal bleeding is a common symptom, often mixed with a mucopurulent discharge, with or without the passage of stool.

In ulcerative proctitis (no colonic involvement) diarrhea may not occur. In such cases, formed stool is passed with blood on the surface of the stool. The diagnosis must not be mistaken for hemorrhoids! Microcytic, hypochromic (iron-deficiency) anemia with a leukocytosis (left shift), and raised inflammatory indices are common (less so in isolated proctitis).

Clinical Course and Complications

Ulcerative colitis is a chronic relapsing, and remitting disease. As well as an acute form with sudden onset of severe diarrhea and systemic upset, relatively mild forms exist in which these features are not present and in which mucopurulent or bloody rectal discharge are the only symptoms.

Local complications include severe bleeding, toxic dilation (megacolon), and perforation. Extra-intestinal complications of ulcerative colitis affect the eyes (e. g., uveitis, episcleritis), skin (erythema nodosum, pyoderma gangrenosum), joints (polyarthralgia, sacroiliitis), blood vessels (vasculitis), and bile ducts (pansclerosing cholangitis).

Diagnosis

The most important investigation in ulcerative colitis is colonoscopy, in particular, examination of the rectum and sigmoid colon. Endoscopy reveals an erythematous, granular mucosa without the normal vascular pattern with contact bleeding on light touch. Larger mucosal lesions (erosions and ulcers) are more commonly observed in the colon than the rectum. The extent of the disease process can also be established at endoscopy.

In contrast to Crohn disease, the distal colorectum is always affected, mucosal disease in the affected bowel is continuous and evenly distributed. With increasing duration of ulcerative colitis there is progressive scarring and shrinkage of the diseased bowel with narrowing and shortening of the affected bowel (drain pipe colon).

Increased Risk of Malignant Disease

The risk of colonic carcinoma is significantly raised in ulcerative colitis, particularly in patients with pancolitis and over 10 years, history of disease (5−8% risk of carcinoma at 15 years, disease duration, 12% risk at 20 years).

In patients with chronic pancolitis (8−10 years) regular colonoscopic surveillance with systematic biopsy is recommended for the early diagnosis of dysplasia and carcinoma.

Toxic Megacolon

In a patient with severe ulcerative colitis the presence of toxic megacolon is indicated by systemic upset, dilated abdomen, and ileus, together with massive colonic dilation (8 cm) on the plain abdominal radiograph. This life-threatening complication has a high risk of perforation and immediate surgical management should always be considered.

Differential Diagnosis

The diagnosis of ulcerative colitis is based on:

• typical clinical history
• characteristic endoscopic findings
• exclusion of other conditions with a similar clinical and endoscopic findings including:
  • Crohn disease − chronic infectious enterocolitis (Entamoeba histolytica, tuberculosis)
  • ischemic colitis
  • radiation colitis
  • pseudomembranous colitis
  • venereal proctitis (Neisseria gonorrhoeae, Chlamydia, herpes simplex virus), differentiation from ulcerative proctitis can be difficult on clinical grounds
  • collagenous colitis and microscopic colitis, endoscopy normal in these conditions.

“Conventional” infectious gastroenteritis (e. g., Campylobacter jejuni) may cause a temporary, self-limiting hemorrhagic colitis. Together with the clinical history and examination, the appearance, distribution, and histology of mucosal lesions on endoscopy and biopsy differentiate ulcerative colitis from Crohn disease. On occasion, it is difficult to differentiate these conditions and overlapping syndromes are known (indeterminate colitis).

---

Venereal Diseases of the Anorectum

The primary manifestation of sexually transmitted disease in the anorectum is not rare, particularly in homosexual men. The majority of these conditions are not specific to this anatomical location, e. g., herpes simplex virus, condylomata accuminata, molluscum contagiosum.

Syphilis can present as perianal condylomata lata. Chlamydia and Neisseria gonorrhoeae cause hemorrhagic proctitis that can be diagnosed by rectal swab and culture. In homosexual men (also patients with HIV) sexual transmission of pathogens such as protozoa and fungi must be considered (e. g., Amoeba, Cryptosporidium, Candida).

Lymphogranuloma venereum causes an ulcerative proctitis limited to the rectum that if not diagnosed and treated appropriately has a tendency to cause scarring with the formation of a rectal stricture 4−5 cm above the anal canal. Mucosal biopsy demonstrates a nonspecific granulomatous inflammation. The differential diagnosis includes carcinoma, Crohn disease, and tuberculosis. The diagnosis is established by rectal swab and culture, or evidence of chlamydial disease on serology.

---

Ischemic (Entero)Colitis

Bloody diarrhea is also observed in ischemic (entero)colitis. This condition is a consequence of either an obliterative angiopathy of blood vessels serving the bowel (e. g., thromboembolism, vasculitis) or reduced perfusion through patent mesenteric vessels (e. g., shock, myocardial infarction, cardiac failure).

The location and extent of affected bowel depends on the regional anatomy of the mesenteric blood supply (celiac trunk, superior mesenteric artery, inferior mesenteric artery). The splenic flexure, descending and sigmoid colon are the most commonly affected segments.

The diagnosis of ischemic bowel is suggested if symptoms present during or immediately after an episode of cardiovascular shock or if a clear history of postprandial abdominal pain (mesenteric angina) is present. Ischemic colitis has been described after vascular graft surgery for aortic or aorto-iliac disease in which the inferior mesenteric artery is sacrificed and the blood supply through the remaining vessels is insufficient. An aorto-iliac steal syndrome has also been described.

Ischemic colitis has been observed in patients with coagulation disorders, women taking the contraceptive pill, systemic vasculitis, and even in long-distance runners. Mesenteric ischemia can also occur proximal to stenotic lesions (e. g., cancer) in the sigmoid and rectum. Isolated ulcers at the splenic flexure, descending or sigmoid colon may indicate ischemia.

READ MORE: Acute Mesenteric Ischemia – An Overview

---

Crohn Disease (Segmental Granulomatous Ileocolitis)

Clinical Features

The presentation of Crohn disease is similar to ulcerative colitis; with the important difference that bloody diarrhea is less common and abdominal pain, fever, and weight loss are more common. The condition is a chronic inflammatory bowel disease of unknown etiology.

The inflammatory process involves the full thickness of the bowel wall and can affect any part of the gastrointestinal tract; most commonly the right colon and terminal ileum. Patchy segmental involvement is typical with areas of macroscopically normal and inflamed mucosa observed on endoscopy. The small bowel is affected in 30−35%, the terminal ileum and right colon in 40−45%, and the left colon in 15− 20%. In contrast to ulcerative colitis, the distal colon and rectum are often spared (i. e., normal sigmoidoscopy). However, perianal complications, commonly fistula, are present in 30−35%.

Laboratory tests usually reveal a mild to moderate anemia and leukocytosis with toxic granulation. Thrombophilia and raised inflammatory indices are common. Low albumin, as a result of the inflammatory enteropathy, is often observed. Evidence of malabsorption (e. g., steatorrhea, vitamin B12 deficiency) may be present in ileal disease.

Clinical Course and Complications

Crohn disease typically follows a chronic course over years with exacerbations and long remissions. Acute, severe exacerbations are rare compared to ulcerative colitis and lifethreatening complications such as severe bleeding and free perforation are exceptional. Rather, stenotic disease with recurrent episodes of obstruction is common, especially in small bowel disease. Transmural fistulae with local abscess formation are also observed.

Systemic complications also occur, most commonly affecting the joints (e. g., polyarthralgia), skin (e. g., erythema nodosum), and eyes (e. g., uveitis). In contrast to ulcerative colitis, postoperative complications are common following bowel resection for Crohn disease, with local recurrence at the anastomosis occurring in over 50% of cases.

Diagnosis

The diagnosis of Crohn disease is based on typical endoscopic and radiological findings demonstrating segmental, discontinuous distribution of disease with areas of deep transmural, linear, and polymorphic ulceration resulting in a cobblestone appearance of the affected bowel.

Differential Diagnosis

The clinical, endoscopic, and radiological findings of Crohn disease may also occur in chronic infections of the gastrointestinal tract (e. g., actinomycosis, tuberculosis, Yersinia, Campylobacter) as a consequence of medications (e. g., nonsteroidal antiinflammatory agents), in malignant lymphoma, diverticulitis, or intestinal ischemia. As a result, the diagnosis of Crohn disease should be made with caution if presenting for the first time with an acute episode.

---

Gastrointestinal Tuberculosis

Clinical Features

The ileocecal region is the most common site for gastrointestinal tuberculosis causing diarrhea, abdominal pain, and weight loss. Gastrointestinal tuberculosis rarely presents as a primary disease in Western populations; it often occurs as a complication of severe disseminated pulmonary disease. In immigrants to Western countries the most common cause is local reactivation of disease, usually with evidence of old pulmonary tuberculosis on chest radiography.

Clinical examination sometimes reveals a fullness in the right iliac fossa on palpation; fecal blood loss is common. Anemia and evidence of chronic infection are rarely absent on laboratory testing.

Investigation

In addition to typical changes on chest radiography and the presence of acid-fast bacilli in the sputum, gastrointestinal endoscopy and radiology reveal infiltration, ulceration, and deformation of the cecum and ascending colon. The differential diagnosis for these findings is that of inflammatory bowel disease. Histology and evidence of tuberculosis on culture of biopsy specimens are diagnostic.

---

Malignant Small Bowel Tumors

Epidemiology

Small bowel malignancy is very rare. When it occurs, small bowel adenocarcinoma is most often seen in the duodenum, becoming less common in the jejunum and ileum. This contrasts with lymphoma, which is more common in the distal small bowel. Carcinoid tumors (see below) and gastrointestinal stromal tumors (GIST) are other potentially malignant tumors of the small bowel.

Clinical Features

Malignant and benign small bowel tumors become symptomatic when their size and location leads to partial or complete bowel obstruction with postprandial colic, nausea, and vomiting. Tumors that are not obstructive are usually asymptomatic or present with nonspecific abdominal symptoms, which are difficult to associate with the tumor.

Malignant small bowel tumors also cause bleeding (often occult anemia) and perforation. Diarrhea occurs in association with hormone-secreting, neuroendocrine small bowel tumors.

Small bowel lymphoma sometimes cause diarrhea, anemia, and B-symptoms (fever, night sweats, weight loss) before bowel obstruction occurs.

In patients with HIV, Kaposi sarcoma must also be considered as a cause of altered bowel habit, gastrointestinal bleeding, and more rarely, bowel obstruction.

Diagnosis

In patients with bowel obstruction, radiological investigations (computed tomography [CT] or abdominal radiography) demonstrate ileus (dilated bowel, multiple fluid levels) above the stenosis caused by the tumor. Only for duodenal tumors can conventional upper gastrointestinal endoscopy be used to demonstrate and perform biopsies.

In patients with abdominal symptoms without obstruction, in whom a small bowel tumor is suspected, the following investigations can be applied: radiological investigations of the small bowel (classic double-contrast studies of the small bowel, CT, or magnetic resonance imaging [MRI] small bowel imaging), enteroscopy, and capsule endoscopy. Radiologic investigations are diagnostic only for relatively large tumors.

Push enteroscopy can detect and biopsy lesions in the proximal one-third of the small bowel. A more complete, noninvasive visual representation of the complete small bowel is possible with double balloon enteroscopy or capsule endoscopy. Radiology and capsule endoscopy provide a provisional diagnosis. However, histological confirmation is not possible. In this situation surgery provides definitive diagnosis and therapy.

---

Benign Small Bowel Tumors

More than half of all small bowel tumors, including adenoma, leiomyoma, lipoma, and angioma, are benign. In most cases these are asymptomatic and are chance findings at surgery or autopsy. Symptoms only occur when these lesions cause small bowel obstruction.

---

Colorectal Carcinoma

Epidemiology

Colorectal carcinoma is the second or third most common malignant disease in Western populations. The lifetime risk of developing colorectal cancer is approximately 5%. The incidence increases with age in a linear fashion.

Clinical Features

Most colorectal cancers remain asymptomatic until the disease is at an advanced stage. Good general health does not exclude underlying colorectal carcinoma; abdominal pain independent of defecation is rarely present. The most common presentation is a change in bowel habit. Large tumors can occasionally be palpated on abdominal examination. Bleeding can occur from the surface of the tumor leading to anemia or overt rectal bleeding.

Anemia of unknown cause and/or rectal bleeding must always raise the suspicion of colorectal carcinoma and must be investigated by urgent endoscopy.

Occult blood loss may be present before other symptoms develop and can be used for early detection of colorectal carcinoma (fecal occult blood test). This investigation is only appropriate as a screening test in asymptomatic patients. Those patients with anemia or overt rectal bleeding must be investigated by endoscopy. Fecal occult blood testing is superfluous in this situation.

Advanced colon carcinoma occasionally causes large bowel obstruction. Complete obstruction causes an acute abdomen, nausea, and vomiting with dilated large and small bowel above the stenosis. This acute presentation is usually preceded by a change in bowel habit and stool consistency with alternating constipation and diarrhea, bloating, and abdominal colic.

Rectal carcinoma rarely causes obstruction and presents with tenesmus and continence problems (involuntary passage of stool with wind), although these symptoms are nonspecific.

The possibility of colorectal carcinoma must be considered in all patients with a change in bowel habit, especially those above the age of 40.

Occasionally, the first presentation of colorectal carcinoma is as a consequence of metastatic liver disease (e. g., hepatomegaly, jaundice, weight loss). In these cases imaging by ultrasound, CT, or MRI (with guided liver biopsy) is crucial to establish the diagnosis.

Fever and sepsis may also be the first manifestation of colorectal carcinoma; probably because the tumor facilitates the translocation of bacteria into the blood stream from the bowel.

Diagnosis

If alarm symptoms (e. g., change of bowel habit, rectal bleeding, anemia) raise suspicion of colorectal carcinoma a colonoscopy must be performed. Conventional radiology (e. g., barium enema) has an auxiliary role in patients with narrow stenosing lesions that the endoscope cannot pass. So-called “virtual colonoscopy” (CT or MRI colonoscopy) may be available if colonoscopic examination is incomplete.

Only deep-seated rectal tumors can be detected by digital examination and this is not a reliable screening test in any circumstances because so few lesions can be palpated.

Serological carcinoembryonic antigen (CEA) assessment and fecal occult blood testing (a screening test in asymptomatic patients) are not appropriate investigations for the diagnosis of colorectal cancer.

---

Colorectal Polyps

Colorectal Polyps Epidemiology

Almost 50% of individuals in Western populations will develop a colorectal polyp in their lifetime. Colorectal polyps can be divided into two main groups based on histology:

• nonneoplastic, hyperplastic polyps that very rarely carry a risk of malignant change
• neoplastic, adenomatous polyps (tubular, villous, or tubulo-villous adenoma); approximately 10% of these polyps will develop into colorectal carcinoma in a period of five to 10 years and are considered to be precancerous lesions. Juvenile polyps (hamartoma) are a further, very rare polypoid lesion of the large bowel.

Clinical Features

Colorectal polyps are usually asymptomatic. Similar to colorectal carcinoma, rectal bleeding and obstructive symptoms (e. g., change in bowel habit) only occur with large lesions. However, villous adenoma occasionally presents with the passage of rectal mucous and diarrhea, rarely with secondary hypokalemia. The diagnosis of colorectal polyps is usually made at colonoscopy.

The indications for investigation are usually symptoms that are not associated with the presence of polyps (e. g., abdominal pain). Because of the high prevalence of precancerous colorectal polyps many countries recommend screening investigations for asymptomatic individuals above 50 years. Patients in whom a colorectal polyp has developed are at an increased risk of developing further polyps and should be entered into a colonoscopic surveillance program.

Diagnosis

The majority of colorectal polyps are asymptomatic. Therefore, most of these lesions are incidental findings at colonoscopy. Most polyps can be completely resected during the same investigation. This provides a histological diagnosis that is important for prognosis.

Colorectal adenoma are precancerous and their removal at endoscopy can reduce the incidence of colorectal carcinoma by up to 80%.

---

Hereditary Colorectal Carcinoma

A variety of genetic mutations can increase the risk of colorectal polyps and carcinoma. The presentation of patients with these conditions and the investigation of their symptoms are similar to those with sporadic polyps and carcinoma.

Hereditary nonpolyposis colorectal carcinoma (HNPCC) or Lynch syndrome is the most common of these rare syndromes (3−5 %). This condition is inherited in an autosomal dominant manner. Colorectal carcinoma usually develops in affected individuals after the age of 45. The incidence of other malignancies is increased by the same mutation (e. g., endometrial, urogenital, ovarian, gastric, etc.).

The second most common form (0.5−1 %) of hereditary colorectal carcinoma is familial adenomatous polyposis (FAP). The cause is a mutation on the adenomatous polyposis coli (APC) gene on chromosome 5 and is also inherited in an autosomal dominant manner. Patients develop hundreds to thousands of colorectal polyps during adolescent years and always develop cancer. For this reason prophylactic panproctocolectomy is recommended to these individuals at a young age.

A variant of FAP is Gardener syndrome, a condition defined by the presence of colorectal polyps with mesenchymal neoplasms including osteoma, fibroma, and desmoid tumors. From around 45 years of age a proportion of FAP patients develop a malignancy at the ampulla of Vater; usually presenting with extrahepatic jaundice.

Turcot syndrome (adenoma combined with brain tumors), Cronkite−Canada syndrome (hamartoma with alopecia and nail dystrophia), and Peutz−Jeghers syndrome (hamartoma throughout the gastrointestinal tract with perioral pigmentation) are further hereditary syndromes that are associated with increased incidence of colorectal carcinoma.

In the two most prevalent hereditary colorectal cancer syndromes (HNPCC, FAP) genetic testing reveals typical mutations in most patients. Upon detection of a hereditary cancer syndrome in a patient, first degree family members should be offered appropriate screening.

The possibility of hereditary colorectal carcinoma should be considered in all patients that develop colorectal polyps under age 50. Always obtain a family medical history.

---

Diverticulosis and Diverticulitis

Epidemiology

A large proportion of Western populations develop large bowel diverticula with prevalence increasing with age. There is no gender predisposition. At least 1% of these patients develop diverticulitis.

Clinical Features

Diverticulosis is asymptomatic. The condition is often an incidental finding on colonoscopy and is most common in the sigmoid colon. There is an epidemiological association between diverticulosis and constipation, although the pathological link is unclear.

Diverticulitis is a local bacterial infection, which is probably the result of a local perforation in the region of a diverticulum. The severity of diverticulitis, localization, and extent of abdominal pain depends on the site of disease, degree of peritoneal irritation, and spread of infection. On occasion, extensive perforation occurs with diffuse peritonitis and abscess formation. Most commonly, diverticulitis causes local, usually left-sided, abdominal pain, sometimes termed a “left-sided appendicitis.”

Complications

Other complications of diverticulosis include diverticular bleeding and a portion of patients develop large bowel stenosis (usually in the sigmoid colon); probably as a result of muscle wall thickening and recurrent diverticulitis. Stenosis can cause a change in bowel habit with alternating constipation and diarrhea. More severe narrowing causes partial bowel obstruction with abdominal colic and bloating.

Rare complications of diverticulitis include dysuria caused by an inflamed diverticulum in close proximity to the bladder and even fistula formation between the bowel and the bladder. In the latter case bowel gas can pass with the urine (pneumaturia). Similarly, left-sided hydronephrosis has been reported as a complication of sigmoid diverticular disease.

Diagnosis

Uncomplicated diverticulosis is often an incidental finding at colonoscopy or barium enema. However, the diagnosis of diverticulitis is not established at endoscopy but rather by CT. Ultrasound or MRI are alternative diagnostic techniques. The condition is recognized by the presence of thickened colonic wall and, if present, local abscess formation.

Chronic Diarrhea Without Abnormal Findings on Endoscopy

Lactase Deficiency

The possibility of lactase deficiency should be considered in patients with diarrhea of unknown cause. Congenital lactase deficiency has been described in infants.

Acquired lactase deficiency and milk intolerance can develop in adults (very frequent in noncaucasians). In acquired lactase deficiency (i. e., milk tolerated in childhood) diffuse abdominal discomfort, bloating, flatulence, and diarrhea develop after ingestion of milk. The diagnosis can be confirmed by a lactose tolerance test with assessment of hydrogen gas in the breath after a 50 g lactose test meal. A rise in hydrogen gas in expired air (to above 20 ppm) with the development of typical symptoms indicates lactase deficiency in the small bowel mucosa. Elimination of significant quantities of milk from the diet is therapeutic.

In addition to the idiopathic form, secondary lactose intolerance is frequently caused by a number of gastrointestinal diseases (e. g., infectious gastroenteritis, celiac disease, Crohn disease). Further rare causes of disaccharidase deficiency include: sucrose-isomaltose intolerance in children (a congenital, autosomal recessive disease) and trehalose intolerance (following ingestion of certain fungi).

Psychogenic Diarrhea

Diarrhea is known to occur with anxiety states, such as fear of an upcoming event (e. g., examinations); an impressive demonstration of psychosomatic regulation. Affected individuals are usually those who react sensitively to external stressors. Upon direct questioning, a long history of variable bowel habit is often obtained and psychogenic diarrhea probably belongs to the same category of conditions as irritable bowel syndrome (although by definition abdominal pain is absent).

Malassimilation (Maldigestion and Malabsorption)

Introduction

Chronic diarrhea and weight loss are suggestive of a malassimilation syndrome if symptoms and signs of nutritional deficiency are present, e. g., macrocytotic (folate or vitamin B12 deficiency) or microcytic, hypochromic (iron-deficiency) anemia, peripheral edema (hypoproteinemia), tetany, bone pain (calcium and vitamin D deficiency), hemorrhagic diathesis (vitamin K deficiency), glossitis, and peripheral neuropathy (vitamin B deficiency).

Pathogenesis

Malassimilation can be caused by many different disturbances of the digestive process. The end effect of these conditions is the loss of essential nutrients from the diet with the stool. The causes of malassimilation can be divided into two main groups (maldigestion and malabsorption) and various subgroups.

Maldigestion is caused by deficiencies of bile or digestive enzyme secretion (or action) resulting in impaired emulsification of fat or hydrolysis of carbohydrate, protein, or fat into smaller molecules.

Malabsorption is characterized by impaired uptake of the products of digestion from the lumen of the bowel into the blood and lymphatic systems. Causes include:

• mucosal disease (e. g., celiac disease, Crohn disease)
• reduced absorptive surface (e. g., small bowel resection, entero-enteric fistula)
• reduced contact time (e. g., carcinoid syndrome)
• disturbed mesenteric blood supply (e. g., mesenteric ischemia) or lymphatic drainage (e. g., tuberculosis, malignancy).

Clinical Features

The most reliable, objective sign of malassimilation is the presence of steatorrhea, i. e., stool fat excretion in excess of 7 g/day at a dietary intake of 100 g/day. However, steatorrhea is absent in the rare, inherited malabsorption conditions in which an isolated failure of the small bowel impairs digestion or absorption of particular nutrients (e. g., disacharidase deficiency, glucose−galactose transporter dysfunction, Hartnup disease, and other syndromes related to amino acid malabsorption). In contrast, steatorrhea is likely to be present in patients that present with oily, odiferous, high-volume diarrhea over 300 g/day.

Diagnosis

The investigation of malassimilation must address two questions:

• Is malassimilation present? (Biochemical evidence of nutritional deficiency or steatorrhea.)
• If yes, what is the cause? (Small bowel assessment by endoscopy and biopsy, radiology, assessment of pancreatic function.)

The blood count and “small bowel screen” are important for the diagnosis of malassimilation. Anemia is usually present in celiac disease and may be the only indication of disease in some patients. Typically, there is a polymorphic picture with evidence of iron, folate, and vitamin B12 malabsorption. Primary pernicious anemia is easily distinguished by the presence of gastric (not duodenal) atrophy and the presence antiparietal cell antibodies. In addition, 50% of patients with celiac disease have Howell−Jolly bodies on the blood film indicative of splenic atrophy.

The “small bowel screen” should include important biochemical markers that are abnormal in malabsorption such as reduced albumin, urea, calcium, phosphate, iron, serum lipids, prothrombin, and raised alkaline phosphatase (osteomalacia). Abnormalities of blood count and “small bowel screen” are usually less marked in maldigestion.

---

Primary Malabsorption – Celiac Disease (Endemic Sprue)

Pathogenesis

Celiac disease in adults and children is caused by a gluten-sensitive, immune-mediated enteropathy (gluten or gliadin is a protein found in cereal crops, including wheat, barley, and rye). In certain individuals (genetic predisposition) the presence of gluten in the diet triggers immune-mediated mucosal damage in the small bowel. This is usually reversible after exclusion of gluten from the diet.

New methods of screening in Europe have shown that celiac disease is one of the most common genetic diseases with a prevalence of between 1:130 and 1:300. The probability that first degree relatives are affected lies between 10−20%. The disease affects both sexes with equal frequency and presents most commonly in middle age, with a tendency to abrupt changes in clinical course (e. g., occult to overt disease).

Clinical Features

The fully developed disease presents with severe diarrhea, significant weight loss, general weakness, and typical features of nutritional deficiencies that clearly point to the diagnosis. In this situation the diagnosis is quickly confirmed by specific investigations. In patients with a short history and severe disease the clinical differential includes underlying malignancy.

The further differential diagnosis of celiac disease includes Crohn disease, hyperthyroidism, anorexia nervosa, severe laxative abuse, and Addison disease.

Atypical and occult presentations of celiac disease are up to 10 times more frequent than that of the fully developed clinical picture. Patients often present with mono- or oligosymptomatic disease. The diagnosis is often delayed in those with isolated iron deficiency anemia or osteomalacia until malabsorption is considered and appropriate investigations performed.

In 5−10% of patients with celiac disease diarrhea is absent. There may even be a tendency to constipation. The most important complication of untreated celiac disease is the increased risk of intestinal malignancy, in particular T-cell lymphoma. This risk is particularly high in patients with refractory sprue, ulcerative jejunitis, and the rare collagenous sprue; all conditions that do not respond to the gluten-free diet.

In severe disease, physical examination may reveal, in addition to cachexia, a bloated “doughy” abdomen, peripheral edema, hypotonia, and increased skin pigmentation (without mucosal pigmentation in contrast to Addison disease). These findings are absent when the disease is controlled.

Diagnosis

The diagnosis of celiac disease is suggested by serological tests and confirmed by small bowel biopsy. IgA and IgG antigliadin antibodies do not have sufficient specificity or sensitivity for diagnosis, indeed antigliadin IgA antibodies can be detected in up to 90% of healthy, elderly individuals. In contrast antiendomysial antibodies offer high diagnostic accuracy.

The antigenic target for antiendomysial antibodies was recently discovered to be the enzyme tissue transglutaminase. The detection of specific IgA and IgG transglutaminase antibodies further increase the specificity and sensitivity of serological tests.

The typical clinical presentation, positive serology, and typical changes on small bowel histology all suggest the diagnosis of celiac disease. Confirmation is provided if a gluten-free diet produces clinical remission, reduction in autoantibody titers, and normalization of small bowel histology.

This response is important because identical histology is found in tropical sprue and hypogammaglobulinemia with sprue. Similar changes are also found in a range of other intestinal disorders (e. g., gastric resection, parasitic infection, certain medications) although these tend to be localized rather than diffuse findings.

In other causes of malassimilation small bowel histology is either normal (e. g., maldigestion, postresection, endocrine− hormonal disease) or demonstrates changes diagnostic of other conditions (e. g., Whipple disease, amyloidosis, intestinal lymphangiectasia, abetalipoproteinemia).

Tropical Sprue

Tropical sprue is an infectious disease (unknown pathogen) that occurs primarily in the Far East, India, Central America, and Puerto Rico. The clinical presentation is similar to celiac disease. However, here the condition responds to antibiotics rather than dietary therapy.

---

Maldigestion and Secondary Malabsorption

Steatorrhea without abnormal small bowel histology suggests the presence of secondary malabsorption or maldigestion. Steatorrhea caused by obstruction of the biliary tract is easy to recognize because of concurrent jaundice.

Typical findings in pancreatic steatorrhea due to chronic pancreatitis include pancreatic calcification, exocrine pancreatic insufficiency, and an abnormal glucose tolerance test.

---

Steatorrhea and Bile Acid Malabsorption

Whipple Disease

Whipple disease is a rare condition that usually presents in a manner similar to celiac disease. Early recognition of this potentially lethal disease is important because effective treatment is available. Whipple disease most commonly affects middle-aged men.

Rheumatic symptoms typically present before those of malassimilation, sometimes by several years. The diagnosis is based on the presence of pathognomonic PAS-positive macrophages in the small bowel biopsy. On ultrasound or at laparotomy, enlarged mesenteric lymph nodes are evident.

The Gram-positive intracellular bacteria that causes Whipple disease, Tropheryma whippelei, has recently been identified and cultured. PCR techniques are now available allowing direct confirmation of the infectious agent. Prolonged antibiotic therapy can induce long-term remission and cure the disease.

Small Bowel Bacterial Overgrowth (SBO)

Pathogenesis. There are almost no bacteria in the proximal small bowel, but the level of colonization increases through the ileum although not to the levels observed in the colon. Small bowel bacterial overgrowth (SBO) is commonly present after ileocecal resection or formation of a blind-ending small bowel loop. Rare causes of SBO include small bowel diverticula, fistula, stenosis, or severe disturbances of small bowel motility (e. g., scleroderma). Increased bacterial colonization of the small bowel increases bile acid deconjugation leading to triglyceride malabsorption and steatorrhea. In addition, deconjugated bile acid has a direct toxic effect on small bowel mucosal function, inhibiting sodium resorption by the enterocytes. In addition, bacterial overgrowth impairs vitamin B12 absorption, although folate levels are increased (produced by bacterial metabolism).

Clinical Features. Patients with SBO may be asymptomatic or present with evidence of malabsorption. Common symptoms include diarrhea, steatorrhea, and vitamin B12 deficiency anemia.

Diagnosis. The diagnostic “gold standard” is quantitative bacterial culture of jejunal aspirates obtained at endoscopy; a population density of 105 bacteria/mL is considered pathologic. Alternatively the diagnosis is suggested by a positive hydrogen breath test (75 g glucose test meal); a simple but nonspecific investigation. The ideal treatment of SBO is management of the underlying condition. This is rarely possible and antibiotic therapy to reduce bacterial overgrowth is usually attempted. This can achieve several months of clinical remission in some patients, whereas relapse occurs in others within weeks.

Short Bowel Syndrome

Extensive small bowel resection causes secondary malabsorption due to reduction in the absorptive area of the bowel, reduced gastrointestinal transit time, and bile acid malabsorption. Due to the remarkable capacity of the remaining bowel to adapt, if more than 100 cm of ileum remains it is usually possible to maintain adequate nutrition by mouth using careful nutrition and fluid management (especially if the colon is preserved).

Milk products should be avoided as secondary lactase deficiency is common after small bowel resection. Supplements of fat-soluble vitamins are necessary because of steatorrhea. Replacement of vitamin B12 and trace elements is of particular importance after extensive ileal resection.

Intestinal Lymphangiectasia

Intestinal lymphangiectasia is caused by obstruction to the lymphatic drainage of the bowel. This condition can be congenital or acquired secondary to abdominal trauma, malignancy, chronic pancreatitis, and occasionally severe cardiac failure. As a consequence, the transport of chylomicrons and lipoproteins is impaired, leading to fat malabsorption and also a protein-losing state.

The combination of steatorrhea, hypoalbuminemia, and lymphopenia is typical for intestinal lymphangiectasia. The diagnosis is established by small bowel biopsy. Treatment is directed against the underlying condition. Medium-chain triglycerides can reduce diarrhea and steatorrhea because these are not absorbed via the lymphatic system but directly into the blood stream.

Endocrine and Hormonal Causes of Diarrhea

Endocrine Disease

• Hyperthyroidism is a common cause of diarrhea mediated by an endocrine disease; steatorrhea is occasionally present.
• Hypoparathyroidism occasionally causes diarrhea. Note: celiac disease must always be excluded in patients presenting with diarrhea and hypocalcemia.
• Adrenal insufficiency (Addison disease) is occasionally accompanied by diarrhea.
• Severe insulin-dependant diabetes mellitus may cause diarrhea. This is not due to pancreatic exocrine insufficiency, but a diabetic neuropathy affecting the autonomic nervous system. Peripheral neuropathy, together with evidence of autonomic dysfunction in other visceral organs may be present (e. g., orthostatic hypotension, atonic bladder, impotence, abnormal sweating).
• Diabetic autonomic neuropathy/dysfunction is closely related to glucose control and the severity of the underlying disease. Pancreatic disease (chronic pancreatitis, pancreatic cancer) as a cause of both diabetes mellitus and steatorrhea must always be excluded.

Hormone-Secreting Tumors

Diarrhea is a prominent symptom in several rare hormone-secreting tumors of the pancreas (gastrinoma [Zollinger−Ellison syndrome], VIPoma [Verner− Morrison syndrome]) and the gastrointestinal tract (neuroendocrine tumors, carcinoid syndrome). Common features of these conditions include:

• similar embryological origin (neural crest)
• typical morphological and histochemical features
• production of various polypeptide hormones by the same biochemical system (APUD = amino precursor uptake decarboxylation).

Carcinoid Syndrome

Clinical Features. Diarrhea is often the first symptom that occurs in carcinoid disease, often preceding other features by several years. In advanced disease it is present in 75% of cases. However, the possibility of carcinoid syndrome is usually considered by the examining doctor only when flushing occurs . This vasomotor phenomenon is usually accompanied by diarrhea, abdominal colic, and respiratory symptoms, and can be triggered by alimentary (dietary) or emotional stimuli. This is a pathognomonic feature of carcinoid syndrome and is rarely missed. Another classic late symptom is endocardial fibrosis with valvular insufficiency or stenosis exclusively affecting the right heart (Hedinger syndrome). Other patients with carcinoid syndrome present with prominent asthmatic symptoms.

Pathophysiology. Carcinoid syndrome is caused by hormone-secreting, metastatic neuroendocrine tumors (carcinoid) in the gastrointestinal tract, rarely by bronchial neuroendocrine tumors (when present, endocardial fibrosis affects the left heart), and gonadal neuroendocrine tumors (cystic ovarian and testicular teratoma with carcinoid tissue). Carcinoid symptoms may occur as part of a paraneoplastic syndrome caused by carcinoma of the lung, pancreas, stomach, or liver. The most common site of the primary carcinoid tumor, single or multiple, is usually in the ileocecal region. Neuroendocrine tumors occasionally cause small bowel stenosis and present with acute obstruction, more rarely with bleeding. However in general, neuroendocrine tumors of the gastrointestinal tract present with characteristic symptoms, such as flushing, only after the development of liver metastases. Carcinoid syndrome presents most commonly in patients between 40 and 70 years of age, without sexual predisposition.

Diagnosis. The production of 5-hydroxytryptamine (serotonin) is important for diagnosis. The 5-hydroxytryptamine level in the plasma is usually raised. However, it is simpler and more reliable to assess the 5-hydroxyindole acetic acid (5-HIAA) level in the urine over 24 hours. 5-HIAA is an end product of serotonin metabolism that is almost always highly elevated in patients with carcinoid syndrome. The differential diagnosis of carcinoid syndrome is limited. Diarrhea and occasionally steatorrhea can be observed in generalized mastocytosis probably as a result of increased histamine release in the small bowel mucosa.

Verner−Morrison Syndrome (VIPoma)

Diarrhea caused by rare, noninsulin-secreting pancreatic adenomas (Verner−Morrison syndrome) is caused by increased secretion of vasoactive intestinal peptide (VIP). The resulting disease is characterized by massive, watery diarrhea (often 10 L/day) with gross electrolyte depletion and shock (“pancreatic cholera”). Similar to gastrinoma, one or several non--cell adenoma or a diffuse islet cell hyperplasia are present, the removal of which is curative. The tumors can be benign or malignant. It is simple to differentiate VIPoma from gastrinoma by the measurement of serum gastrin.

Caution: diarrhea and hypokalemia are much more commonly caused by laxative abuse.

References

• Fine KD, Schiller LR. AGA technical review on the evaluation and management of chronic diarrhea. Gastroenterology 1999; 116:1464–86.
• Guerrant RL, Bobak DA. Bacterial and protozoal gastroenteritis. N Engl J Med 1991; 325:327–40.
• Guerrant RL, Van Gilder T, Steiner TS et al. Practice guidelines for the management of infectious diarrhea. Clin Infect Dis 2001; 32: 331–51.
• Kaufmann M, Fried M. Enzymdefekte und Malabsorption. In: Adler, Beglinger, Manns, Müller-Lissner, Schmiegel (Hrsg.). Klinische Gastroenterologie und Stoffwechsel Heidelberg: Springer 2000.
• Kaufmann M, Risti B, Fried M. Die Whipple-Erkrankung. Internist 1996; 37:895–902.
• Lynch HT, de la Chapelle A. Genomic medicine: hereditary colorectal cancer. N Engl J Med 2003; 348:919–32.
• Müllhaupt B, Fried M. Chronisch-infektiöse Darmkrankheiten. In: Adler, Beglinger, Manns, Müller-Lissner, Schmiegel (Hrsg.). Klinische Gastroenterologie und Stoffwechsel Heidelberg: Springer 2000.
• Ransohoff DF, Sandler RS. Screening for colorectal cancer. N Engl J Med 2002; 346:40–4.
• Thielman NM, Guerrant RL. Acute infectious diarrhea. N Engl J Med 2004; 350:38–47.