Diarrhea

Diarrhea is the passage of loose or watery bowel movements.

Bowel movements usually occur more frequently, but an increase in the frequency of stool without a change in the consistency is not diarrhea. People who eat large amounts of vegetable fiber, for example, may move their bowels 3 to 5 times a day, but the stool in such cases is usually firm and well formed.

Diarrhea is a common problem among older people. Most often, diarrhea begins suddenly. Although diarrhea is always likely to be annoying, fortunately it typically lasts for a brief period and resolves on its own. However, persistent diarrhea can cause dehydration and requires treatment.

Causes

Diarrhea is the result of the stool containing too much liquid. The excess liquid is primarily water. The amount of water remaining in the stool can become excessive if too little is absorbed from material moving through the digestive tract or if the body adds more water to the material.

Sometimes the excess liquid consists of more than just water. Among people who cannot absorb fats or carbohydrates adequately, excess fats or carbohydrates remain in the stool in addition to excess water, resulting in diarrhea. Among people whose large intestine becomes inflamed or infected, diarrhea can involve a combination of excess water and blood, mucus, and tissue from the lining of the large intestine.

Diarrhea that develops suddenly and lasts briefly is most often caused by an infection resulting from a virus, bacteria, or parasites. Sometimes bacteria produce diarrhea by releasing a toxin. The toxin can end up in the digestive tract even in people who do not have an infection, for example, when food contaminated with the substance is eaten. Other times bacteria that have already infected the intestine release the toxin from within the digestive tract. When diarrhea is caused by microorganisms or ingestion of chemical toxins, it is sometimes referred to as gastroenteritis. Outbreaks of gastroenteritis can occur in sites where people live close together and have frequent contact, such as nursing homes. Alternatively, when diarrhea is caused by food contaminated with microorganisms or toxins, it may be referred to as food poisoning. In some cases, the cause of sudden, brief diarrhea is a new drug, an increase in the dose of a drug, or a change in diet (such as drinking more juice or eating more fruit or dairy products). Rarely, the cause is ischemia of the colon, if the colon's blood supply is suddenly decreased due to a blockage in an artery.

Diarrhea that persists can have a variety of causes. Infection can cause persistent diarrhea. Overgrowth of bacteria normally present in the small intestine is another cause. Clostridium difficile is a type of bacteria that commonly causes such an overgrowth. Overgrowth with C. difficile or with other types of bacteria may occur after treatment with antibiotics.

Eating foods that contain hexitol, sorbitol, and mannitol can also cause persistent diarrhea. Inability to absorb certain nutrients, such as lactose (milk sugar) and fructose can result in diarrhea. People who have difficulty digesting fatty foods may develop diarrhea. Certain drugs can cause diarrhea, including antacids that contain magnesium. People who have had a portion of their intestines removed may develop persistent diarrhea. Rarely, abnormal growths in the digestive tract, such as polyps and tumors, cause persistent diarrhea.

Symptoms

In diarrhea, the consistency of stool can be anything from soft and pasty to completely watery. The color can range from brown to clear. Black stools may indicate bleeding in the digestive tract, although some drugs used to treat diarrhea (those containing bismuth subsalicylate) turn the stools black. When a black color is caused by blood (melena), the stools usually appear tarry and are foul smelling. Rarely, stools are loose and red from blood (for example, if hemorrhoids are present or if ischemia of the colon develops).

Crampy pain and excessive flatulence (gas) may occur. People with diarrhea often feel an urgency to move their bowels. Some people experience nausea, with or without vomiting, especially if the diarrhea is caused by an infection. Fever may develop if the diarrhea is caused by an infection.

Light-headedness and weakness may occur if diarrhea leads to dehydration, which in turn can cause blood pressure to drop. Blood pressure can drop enough to cause fainting (syncope) or heart rhythm abnormalities (arrhythmias). Rapid breathing or shortness of breath, loss of appetite, nausea, and fatigue may occur, causing blood and other body fluids to be too acidic (a condition called metabolic acidosis).

Diagnosis

Diarrhea should be evaluated by a doctor if it is accompanied by light-headedness or blood in the stool or in any case in which it lasts for more than 3 days. A doctor first tries to determine whether the diarrhea began suddenly and has been present for a short time or whether it has been persistent (lasting more than 3 weeks).

When diarrhea is not severe and has lasted less than 1 week, the symptoms and physical examination alone are often enough to determine the cause and necessary treatment. The doctor tries to determine whether changes in drugs or diet may be the cause; whether the person has other symptoms, such as a fever or pain; and whether the person has been exposed to people with an infection.

When diarrhea persists longer than 3 weeks, stool samples may be examined. Examination of stool samples reveals if the stool is formed or watery and if it contains fat, blood, or other substances. The volume of stool over 24 hours may also be determined. Samples can be tested for infectious organisms, including certain bacteria and parasites. The doctor may examine the lining of the anus and rectum using sigmoidoscopy. Sometimes a biopsy (removal and microscopic examination of tissue) of the rectal lining is performed.

Treatment

Treatment of diarrhea depends on its cause. Most people with diarrhea only have to remove the cause and suppress the diarrhea until the body heals itself. For example, diarrhea is sometimes cured when a person eliminates foods that have recently been added to the diet. If diarrhea develops while taking a certain drug, the diarrhea may be cured if the drug can be discontinued or replaced with another drug. If diarrhea is caused by a viral infection, it generally resolves by itself in 24 to 48 hours. Diarrhea caused by a bacterial infection may resolve by itself, but sometimes it requires treatment with an antibiotic. Diarrhea caused by a parasitic infection is treated with antiparasitic drugs.

Many prescription and nonprescription drugs are available for the treatment of diarrhea. Nonprescription drugs include adsorbents (for example, kaolin-pectin), which adhere to chemicals, toxins, and some infectious organisms. Some adsorbents can also help firm up the stool. Bismuth helps many people with diarrhea. One side effect of bismuth is that it turns the stool black. Another nonprescription drug used is loperamide.

Prescription drugs used to treat diarrhea include opioids, codeine, and diphenoxylate. Bulking agents used for chronic constipation, such as psyllium and methylcellulose, can sometimes help relieve chronic diarrhea as well.

Diarrhea tends to cause dehydration if it lasts more than a day or two. As long as the person is not vomiting and does not feel nauseated, drinking fluids containing a balance of water, sugars, and salts can be very effective. One example of such a fluid is 8 ounces of fruit juice mixed with a teaspoon of corn syrup or honey and a pinch of salt, followed by 8 ounces of water mixed with a half-teaspoon of baking soda (sodium bicarbonate).

If, however, the person is vomiting or is unable to drink enough fluids to remain hydrated, hospitalization and treatment with water and salts given intravenously may be necessary.