The Irritable Bowel Syndrome (IBS) or ‘nervous colon’ is the commonest cause of chronic, intermittent abdominal complaints for millions of people all over the world.  The cardinal symptoms are seven: 1. abdominal pain, 2. bloating, 3. Intestinal cramps, 4. diarrhea, 5. constipation, 6. defecation urgency, and 7. relief with defecation.  Although all seven symptoms are not always present in all patients at all times, most patients will experience most of these symptoms over the years.  Nonetheless, the two most distinctive features of the IBS, which are ever present, are chronicity (duration of many months to many years) and intermittency (symptoms come and go depending on many factors).
        The disease can present at any age and can be a) diarrhea predominant, b) constipation predominant, and c) mixed with alternating diarrhea and constipation.  Patients may transition from one form to the other over the years or may have all forms at various times. The disorder can begin spontaneously or after an intestinal infection such as traveller’s diarrhea (post-infectious IBS).  The causes are not well understood but include genetic inheritance, environmental factors, anxiety, emotional trauma, altered bacterial flora, and myriad dietary sensitivities and intolerances.
         The diagnosis is made by ruling out other disorders because there is no diagnostic test for IBS and because the colon always appears normal when scoped.  Clinical diagnosis without supporting studies is safe when the symptoms have been present and unchanged for a long time.  In such cases a treatment trial is reasonable and if successful would avoid expensive and unnecessary workups.  However, if the IBS is recent or if the symptoms have changed drastically, an investigation by a gastroenterologist is in order unless initial, simple treatments succeed.
         There are two uncommon diseases that mimic IBS and need to be ruled out with proper studies: a) Celiac Disease, which is an autoimmune disorder caused by sensitivity to Gluten—a protein present in wheat, barley, and rye—can be ruled out with blood tests and a small intestinal biopsy obtained through an endoscope.  b) Colitis, which may only be visible through a microscope, can be ruled out by colonoscopy with multiple biopsies.
         Other mimicking disorders such as certain hormone-producing tumors can be ruled out with specific blood tests.  Food allergies, although commonly blamed, are seldom implicated in scientific studies but remain a prevalent myth.  Food sensitivities to onions, lettuce, spices, garlic, hot peppers, etc. commonly aggravate the IBS but do not actually cause it.  Lactose intolerance—a condition caused by the weak or deficient intestinal enzyme (lactase) that fails to digest the milk sugar (lactose) —can easily be ruled out by eliminating dairy products from the diet.  If symptoms disappear when dairy products are eliminated and if they reappear when the dairy products are reintroduced, then the diagnosis is confirmed and no further workup is required.
         The Syndrome of Small Intestinal Bacterial Overgrowth (SIBO) has come to the forefront lately with new research indicating that altered intestinal bacteria may contribute to the IBS as well as to Acid Reflux Disease (GERD), which can coexist with it.  Studies show that treating SIBO with non-absorbable antibiotics may cause both the IBS and the GERD to go into remission.  But the story is far from complete because other treatments (daily fiber, antispasmodics, antidepressants, anti-anxiety agents, special laxatives, and certain intraluminal anti-inflammatory agents such as mesalamine or sulfasalazine, and the myriad acid reducing medications) all seem to work in many cases.
         Other less common bacterial infections may also play a part in the IBS. Clostridium difficile, the agent of Antibiotic Colitis, can also mimic the IBS, especially when it becomes chronic.  Luckily, some of the non-absorbable antibiotics used to treat SIBO such as Rifaxamin are also active against C. difficile and may eradicate it and, at the same time, eradicate the undesirable gas-producing bacteria of SIBO.  In such cases, when the IBS is dually caused by SIBO and C. difficile, certain non-absorbable antibiotics might effect a long-term remission.  
         The simplest treatment of the IBS, which should always be tried first, is non-absorbable fiber.  Non-absorbable fiber comes under many names such as Metamucil but is essentially Psyllium hydorphylic mucilloid (ispaghula husk).  Taking enough fiber is often all that is needed to quiet down the IBS.  The Psyllium fiber absorbs and retains water in the gut lumen thus increasing the stool bulk and stool moisture.  Consequently, it has two opposing actions, a dichotomy that has led to wide spread misunderstanding.  By absorbing the excess water in the stool, it prevents diarrhea and by increasing the moisture and bulk of the stool it prevents constipation.
         The IBS is a common, mysterious, complex disorder whose etiologies are still poorly understood and whose treatments are still in evolution.