William C. Shiel Jr., MD, FACP, FACR
William C. Shiel Jr., MD, FACP, FACR
Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.
In this Article
What causes dyspepsia (indigestion)?
It's not surprising that many gastrointestinal diseases have been associated with dyspepsia. However, many non-gastrointestinal diseases also have been associated with dyspepsia. Examples of the latter include diabetes, thyroid disease, hyperparathyroidism (overactive parathyroid glands), and severe kidney disease. It is not clear, however, how these non-gastrointestinal diseases might cause dyspepsia. A second important cause of dyspepsia is drugs. It turns out that many drugs are frequently associated with dyspepsia, for example, nonsteroidal anti-inflammatory drugs (NSAIDs such as ibuprofen), antibiotics, and estrogens). In fact, most drugs are reported to cause dyspepsia in at least some patients.
As discussed previously, most dyspepsia (not due to non-gastrointestinal diseases or drugs) is believed to be due to abnormal function of the muscles of the organs of the gastrointestinal tract or the nerves controlling the organs. The nervous control of the gastrointestinal tract, however, is complex. A system of nerves runs the entire length of the gastrointestinal tract from the esophagus to the anus in the muscular walls of the organs. These nerves communicate with other nerves that travel to and from the spinal cord. Nerves within the spinal cord, in turn, travel to and from the brain. (The gastrointestinal tract is exceeded in the numbers of nerves it contains only by the spinal cord and brain.) Thus, abnormal function of the nervous system in dyspepsia might occur in a gastrointestinal muscular organ, the spinal cord, or the brain.
The nervous system controlling the gastrointestinal organs, as with most other organs, contains both sensory and motor nerves. The sensory nerves continuously sense what is happening (activity) within the organ and relay this information to nerves in the organ's wall. From there, information can be relayed to the spinal cord and brain. The information is received and processed in the organ's wall, the spinal cord, or the brain. Then, based on this sensory input and the way the input is processed, commands (responses) are sent to the organ over the motor nerves. Two of the most common motor responses in the intestine are contraction or relaxation of the muscle of the organ and secretion of fluid and/or mucus into the organ.
As already mentioned, abnormal function of the nerves of the gastrointestinal organs, at least theoretically, might occur in the organ, spinal cord, or brain. Moreover, the abnormalities might occur in the sensory nerves, the motor nerves, or at processing centers in the intestine, spinal cord, or brain.
Some researchers argue that the cause of functional diseases is abnormalities in the function of sensory nerves. For example, normal activities, such as stretching of the small intestine by food, may give rise to sensory signals that are sent to the spinal cord and brain, where they are perceived as painful. Other researchers argue that the cause of functional diseases is abnormalities in the function of motor nerves. For example, abnormal commands through the motor nerves might produce painful spasm (contraction) of the muscles. Still others argue that abnormally functioning processing centers are responsible for functional diseases because they misinterpret normal sensations or send abnormal commands to the organ. In fact, some functional diseases may be due to sensory dysfunction, motor dysfunction, or both sensory and motor dysfunction. Others may be due to abnormalities within the processing centers.
An important concept that is relevant to these several potential mechanisms (causes) of functional diseases is the concept of "visceral hypersensitivity". This concept states that diseases affecting the gastrointestinal organs (viscera) "sensitize" (alter the responsiveness of) the sensory nerves or the processing centers to sensations coming from the organ. According to this theory, a disease such as colitis (inflammation of the colon) can cause permanent changes in the sensitivity of the nerves or processing centers of the colon. As a result of this prior inflammation, normal stimuli are perceived (felt) as abnormal (for example, as being painful). Thus, a normal colonic contraction may be painful. It is not clear what prior diseases might lead to hypersensitivity in people, although infectious diseases (bacterial or viral) of the gastrointestinal tract are mentioned most often. Visceral hypersensitivity has been demonstrated clearly in animals and people. Its role in the common functional diseases, however, is unclear.
Another potential cause of dyspepsia is bacterial overgrowth of the small intestine (small intestinal bacterial overgrowth or SIBO), although the frequency with which this condition causes dyspepsia has not been determined, and there is little research in the area. The relationship between overgrowth and dyspepsia needs to be pursued, however, since many of the symptoms of dyspepsia are also symptoms of bacterial overgrowth. Overgrowth can be diagnosed by hydrogen breath testing and is treated primarily with antibiotics.
Other diseases and conditions can aggravate functional diseases, including dyspepsia. Anxiety and/or depression are probably the most commonly-recognized exacerbating factors for patients with functional diseases. Another aggravating factor is the menstrual cycle. During their periods, women often note that their functional symptoms are worse. This corresponds to the time during which the female hormones, estrogen and progesterone, are at their highest levels. Furthermore, it has been observed that treating women who have dyspepsia with leuprolide (Lupron), an injectable drug that shuts off the body's production of estrogen and progesterone, is effective at reducing symptoms of dyspepsia in premenopausal women. These observations support a role for hormones in the intensification of functional symptoms.
Medically Reviewed by a Doctor on 4/15/2014
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