Causes of diarrhea? 
Diarrhea affects all of us from time to time and is generally transient in nature, treated successfully by over-the-counter medications or altered diets. Patients generally seek medical attention when their diarrhea becomes more pronounced, prolonged, associated with fever, abdominal pain or rectal bleeding.

There are many different conditions that can lead to diarrhea, so when you visit your doctor, a detailed and accurate history is important. Your doctor will likely ask about the frequency, volume, duration and consistency and quality of the stool along with associated symptoms such as blood, mucous, puss, abdominal pain, fever, weight loss, etc.

Knowledge of your medications is important, especially if there has been a change recently, as these can certainly affect your bowel habits.

Be sure to tell your doctor about any other underlying medical conditions you may have, as this could be involved or result in diarrhea, as well. In that regard, all medical problems, past surgeries and family history are important factors in considering the cause for diarrhea. 
Other important factors:

  • Travel history 
  • Diet 
  • Medications (prescription and over-the-counter) 
  • Psychological stress 

A thorough dietary history is important to know. Certain poorly-absorbed foods may bring on symptoms of diarrhea.

Your doctor will likely perform a physical examination to evaluate your vital signs, temperature, and overall physical condition, with particular attention to the abdomen. He may also ask for stool samples for culture and the detection of blood.

Diarrhea is classified as either acute or chronic in nature. 

Acute diarrhea

Acute diarrhea is generally defined as diarrhea that has been present for less than several weeks. It presents with a sudden change in bowel habits, resulting in loose and frequent stools more voluminous in nature, sometimes associated with fever, malaise and/or dehydration. 

Causes. Infections are the most common cause of acute diarrhea. The organisms we see most frequently are E. Coli, Salmonella, Shigella, Clostridium Difficile (C. Difficile), Campylobacter and Giardia, as well as a variety of viral causes. Food poisoning is another cause of acute diarrhea, which is a result of various bacteria infecting food that has generally been stored improperly. 

Numerous medications may cause diarrhea. These can include antacids, antibiotics, antihypertensive medications, laxatives, magnesium supplements, potassium supplements and various cardiac medications. 

Ingestion of poorly-absorbed sugar may lead to diarrhea in certain people. These include fructose, lactose, mannitol and sorbitol. Some of these products are present in sugarless foods or drinks, and this is a quite common cause of acute diarrhea. 

Diagnosis. An evaluation of acute diarrhea consists of a visit with the doctor that includes a history and physical examination. Sometimes a flexible sigmoidoscopy is performed to look at the lining of the colon, and we may perform stool cultures and analysis to look for infectious causes. Blood tests or abdominal x-rays may also be considered. 

Treatment. Treatment for acute diarrhea consists mainly of replenishing fluid and electrolytes, along with antibiotics and antidiarrheal agents. Most patients respond well to outpatient treatment, but on occasion if severe dehydration develops or signs of toxicity occur, like fever or severe pain, then in that situation the patient may need to be hospitalized. 

Chronic diarrhea

Chronic Diarrhea is defined as diarrhea that persists for more than 4 weeks. 

Causes. There are many possible causes for chronic diarrhea:

  • Infections do not generally cause this condition. 
  • Medications– Medications may cause drug-induced diarrhea may without you realizing it. An example may be as simple as an antacid, which could lead to diarrhea if you are taking on a regular basis, as most of these contain magnesium. 
  • Surgery – We may see this condition after certain surgeries are performed; in particular, a vagotomy or gastrectomy, cholecystectomy (gallbladder removal) or bowel resection. 
  • Abdominal pelvic radiation therapy.
  • Endocrine diseases, including hyperthyroidism, diabetes mellitus, hypoparathyroidism or Addison's disease. 
  • Circulatory problems, such as congestive heart failure, vasculitis or poor bowel circulation. 
  • Immune deficiencysyndromes like AIDS or various neurologic diseases. 
  • Chronic bacterial infections also can be a cause -- the most common of these would be tuberculosis, or parasites like Giardia, Strongyloides, Yersinia. 
  • Inflammatory bowel disease, such as Crohn's disease, ileitis, or ulcerative colitis.These conditions lead to chronic inflammation of the lining of the bowel wall, resulting in seepage of secretions, mucous, blood and hypermotility, all resulting in chronic diarrhea. 
  • Occasionally diverticulitis of the colon or a collagenous colitis might also be a factor. 
  • Tumors of the colon, especially those in the lower part of the colon. These could be either colon cancers or colon polyps, as well as abdominal lymphomas or carcinoid tumors.
  • Glandular tumors like pancreatic carcinoma, gastrinoma, thyroid carcinoma or carcinoid tumors can also lead to diarrhea. 
  • Maldigestion or malabsorption – This could be secondary to a decrease in production of digestive enzymes from either the pancreas or the bile, resulting in poor absorption and thus diarrhea. Additionally, certain conditions of the lining of the small intestine, which prevent absorption of food and nutrients can result in a diarrhea state.

Diagnosis. In order to diagnose the cause of chronic diarrhea, a rather extensive work-up may be necessary. First of all it includes a careful history and physical examination. Various tests are employed, including blood counts, serum chemistries, liver function and thyroid tests, urine evaluation, stool examination for bacteria as well as parasites and blood and a possible stool collection for fat or electrolytes. 

Colonoscopy and/or upper endoscopy are frequently employed to evaluate the inside of the gastrointestinal (GI) tract and take specimens if necessary. Occasionally, upper or lower GI x-rays are also employed, as well as abdominal and pelvic sonography or CT scans of the abdomen.

Treatment. There is no one treatment for chronic diarrhea. The approach is dependent upon the actual cause, so once a work-up is completed, therapy can be directed at the specific cause for the chronic diarrhea. In rare cases, no cause is determined – this is called a chronic idiopathic diarrhea. In this case, dietary manipulation and various anti-diarrhea medications are employed. 

Diarrhea – loose, watery stools occurring more than three times in one day – is a common problem that usually lasts a day or two and goes away on its own without any special treatment. However, prolonged diarrhea can be a sign of other problems.

Diarrhea can cause dehydration, which means the body lacks enough fluid to function properly. Dehydration is particularly dangerous in children and the elderly, and it must be treated promptly to avoid serious health problems.

People of all ages can get diarrhea. The average adult has a bout of diarrhea about four times a year.