Diarrhea is an increase in the volume, wateriness, or frequency of bowel movements. (See also Diarrhea in Children.)
The frequency of bowel movements alone is not the defining feature of diarrhea. Some people normally move their bowels 3 to 5 times a day. People who eat large amounts of vegetable fiber may produce more than a pound (1/2 kilogram) of stool a day, but the stool in such cases is well formed and not watery. Diarrhea is often accompanied by gas, cramping, an urgency to defecate, and, if the diarrhea is caused by an infectious organism or a toxic substance, nausea and vomiting.
Complications
Diarrhea can lead to dehydration and a loss of electrolytes, such as sodium, potassium, magnesium, chloride, and bicarbonate, from the blood. If large amounts of fluid and electrolytes are lost, the person feels weak, and blood pressure can drop enough to cause fainting (syncope), heart rhythm abnormalities (arrhythmias), and other serious disorders. At particular risk are the very young, the very old, the debilitated, and people with very severe diarrhea.
Causes of Diarrhea
There are many different causes of diarrhea, depending on how long the diarrhea has lasted ( see Table: Some Causes and Features of Diarrhea).
The most common causes of acute diarrhea (lasting less than a week) are
Infection with viruses, bacteria, or parasites (gastroenteritis)
Drug side effects
The most common causes of chronic diarrhea (lasting more than 4 weeks) are
Drug side effects
Diarrhea that has been present for more than 4 weeks may be a lingering case of acute diarrhea or the early stage of a disorder that causes chronic diarrhea.
Classification
Normally, stool is 60 to 90% water. Diarrhea occurs when not enough water is removed from the stool, making the stool loose and poorly formed. Stool may contain too much water if it
Passes too quickly through the digestive tract
Contains certain substances that prevent the large intestine from absorbing water
Contains excess water secreted by the intestines
Rapid passage (transit) of stool is a common cause of diarrhea. For stool to have normal consistency, it must remain in the large intestine for a certain amount of time. Stool that leaves the large intestine too quickly is watery. Many medical conditions and treatments can decrease the amount of time that stool stays in the large intestine. These conditions include an overactive thyroid (hyperthyroidism); Zollinger-Ellison syndrome (a condition of over-production of acid by a tumor); surgical removal of part of the stomach, small intestine, or large intestine; surgical bypass of part of the intestine; inflammatory bowel disease (such as ulcerative colitis); surgical removal of the gallbladder (cholecystectomy
Osmotic diarrhealactose intolerance. The severity of osmotic diarrhea depends on how much of the osmotic substance is consumed. Diarrhea stops soon after the person stops eating or drinking the substance. Blood in the digestive tract also acts as an osmotic agent and results in black, tarry stools (melena). Another cause of osmotic diarrhea is an overgrowth of normal intestinal bacteria or the growth of bacteria normally not found in the intestines. Antibiotics can cause osmotic diarrhea by destroying the normal intestinal bacteria.
Secretory diarrheaCampylobacter) and parasites (for example, Cryptosporidiumgastrinoma, and vipoma—also can cause secretory diarrhea, as can some polyps.
Inflammatory diarrhea occurs when the lining of the large intestine becomes inflamed, ulcerated, or engorged and releases proteins, blood, mucus, and other fluids, which increase the bulk and fluid content of the stool. This type of diarrhea can be caused by many diseases, including ulcerative colitis, Crohn disease, tuberculosis, and cancers such as lymphoma and adenocarcinoma. When the lining of the rectum is affected, people often feel an urgent need to move their bowels and have frequent bowel movements because the inflamed rectum is more sensitive to expansion (distention) by stool.
Diarrhea caused by malabsorption is characterized by oil or grease in the stool and an oily rim around the toilet bowl after stool is flushed. Malabsorption of bile salts, which can result from certain disorders, can cause diarrhea by stimulating water and electrolyte secretion; the stools have a green or orange color.
Evaluation of Diarrhea
Not every episode of diarrhea requires immediate evaluation by a doctor. The following information can help people decide whether a doctor’s evaluation is needed and help them know what to expect during the evaluation.
Warning signs
Certain findings raise suspicion of a more serious cause of diarrhea.
Blood or pus in the stool
Fever
Signs of dehydration (such as decreased urination, lethargy or listlessness, extreme thirst, and a dry mouth)
Chronic diarrhea
Diarrhea at night
Weight loss
When to see a doctor
People who have warning signs of blood or pus in the stool, fever, or signs of dehydration should see a doctor right away, as should those with significant abdominal pain. Such people may need immediate testing, treatment, and sometimes admission to a hospital. If the only warning signs are chronic or nighttime diarrhea or weight loss, people should see a doctor within a week or so. People without warning signs should call a doctor if diarrhea lasts for more than 72 hours. Depending on the person's other symptoms, age, and medical history, the doctor may recommend the person have an examination or try at-home or over-the-counter treatments (see treatment of diarrhea).
What the doctor does
Doctors first ask questions about the person's symptoms and medical history. Doctors then do a physical examination. What they find during the history and physical examination often suggests a cause of the diarrhea and the tests that may need to be done ( see Table: Some Causes and Features of Diarrhea).
A doctor begins by asking how long the diarrhea has been going on and how severe it has been. Simultaneous occurrence of diarrhea in friends, family members, or other personal contacts is sought. Other important questions focus on
Circumstances around when it started (including recent travel, food ingested, and source of water)
Drug use (including any antibiotics within the previous 3 months)
Abdominal pain or vomiting
Frequency and timing of bowel movements
Changes in stool characteristics (for example, presence of blood, pus, oil or grease, or mucus and changes in color or consistency)
Changes in weight or appetite
Feeling an urgent need to defecate or to defecate constantly
The physical examination begins with the doctor's evaluation of the person's fluid and hydration status. A full examination of the abdomen is done, as is a digital rectal examination to check for the presence of blood.
Testing
The need for testing depends on what the doctor finds during the history and physical examination ( see Table: Some Causes and Features of Diarrhea). Acute watery diarrhea (lasting less than about 4 days) without warning signs is usually caused by a viral infection, and people who otherwise appear well do not require testing. People with warning signs of dehydration, bloody stool, fever, or severe abdominal pain typically need testing—particularly those who are very young or very old. In these people, doctors do blood tests to detect blood and electrolyte abnormalities and stool tests to detect blood, markers of inflammation, and the presence of infectious organisms (such as Campylobacter, Yersinia, amebas, Giardia, and Cryptosporidium). Some causes of infection are detected by looking under the microscope, whereas others require a culture (growing the organism in the laboratory) or special enzyme tests (for example, Shigella or Giardia). If the person has taken antibiotics within the past 2 to 3 months, the doctor may test the stool for Clostridioides difficile (formerly Clostridium difficile) toxin. A colonoscopy is usually not necessary.
For diarrhea lasting more than 4 weeks (more than 1 to 3 weeks for people who have a weakened immune system or who appear seriously ill), similar tests are done. In addition, the doctor may test the stool, including tests for fat (indicating malabsorption) , do blood tests, and do a colonoscopy to examine the lining of the rectum and colon and to gather samples to test for infection. People whose symptoms seem related to diet may have a breath test to look for hydrogen, which suggests they are not absorbing carbohydrates. Sometimes a biopsy (removal of a tissue specimen for examination under a microscope) of the rectal lining is done to look for inflammatory bowel disease. Sometimes the volume of stool over a 24-hour period is determined. Imaging tests, such as computed tomography (CT) enterography, may be needed if the doctor suspects certain tumors. If doctors are still uncertain about the diagnosis, they may need to assess the function of the pancreas. Depending on the person's symptoms, doctors may also do tests for thyroid or adrenal gland disease.
Treatment of Diarrhea
Treatment is directed at the cause of diarrhea, when possible. For example, dietary and drug causes are avoided, tumors are removed, and drugs are given to eradicate a parasitic infection. However, in many cases, the body heals itself. A viral cause usually resolves by itself in 24 to 48 hours.
Dehydration
Extra fluids containing a balance of water, sugars, and salts are needed for people who are dehydrated. As long as the person is not vomiting excessively, these fluids can be given by mouth ( see Treatment). Seriously ill people and those with significant electrolyte abnormalities require intravenous fluids and sometimes hospitalization.
Drugs
Salmonella, Shigella, and Clostridioides difficile
Over-the-counter drugs include adsorbents (for example, kaolin-pectin), which adhere to chemicals, toxins, and infectious organisms. Some adsorbents also help firm up the stool. Bismuth helps many people with diarrhea. It has a normal side effect of turning the stool black. Bulking agents used for chronic constipation
Key Points
In people with acute diarrhea, doctors examine the stool only if they suspect people have certain acute infections or if people have prolonged symptoms (that is, more than about 4 to 7 days) or warning signs.
Doctors avoid using antidiarrheal drugs if there is a possibility that the person has Clostridioides difficile, Salmonella, or Shigella.
