Achalasia (cont.)
How is esophageal function abnormal in achalasia?
In achalasia there is an inability of the lower
sphincter to relax and open to let food pass into the stomach. In at least half
of the patients, the lower sphincter resting pressure (the pressure in the lower
sphincter when the patient
is not swallowing) also is abnormally high. In addition to the abnormalities of
the lower sphincter, the muscle of the lower half of the esophagus does not
contract normally, that is, peristaltic waves do not occur, and, therefore, food
and saliva are not propelled down the esophagus and into the stomach. A few
patients with achalasia have high-pressure waves in the lower esophageal body
following swallows, but these high-pressure waves are not effective in pushing
food into the stomach. These patients are referred to as having "vigorous"
achalasia. These abnormalities of the lower sphincter and esophageal body are
responsible for food sticking in the esophagus.
What causes achalasia?
The cause of achalasia is unknown. Theories on causation invoke infection,
heredity or an abnormality of the immune system that causes the body itself to
damage the esophagus (autoimmune disease).
The esophagus contains both muscle and nerves. The
nerves coordinate the relaxation and opening of the sphincters as well as the
peristaltic waves in the body of the esophagus. Achalasia has effects on both
the muscles and nerves of the esophagus; however, the effects on the nerves are
believed to be the most important. Early in achalasia, inflammation can be seen
under the microscope in
the muscle of the lower esophagus, especially around the nerves. As the disease
progresses, the nerves begin to degenerate and ultimately disappear,
particularly the nerves that cause the lower esophageal sphincter to relax.
Still later in the progression of the disease, muscle cells begin to degenerate,
possibly because of the damage to the nerves. The result of these changes is a
lower sphincter that cannot relax and muscle in the lower esophageal body that
cannot support peristaltic waves. With time, the body of the esophagus stretches
and becomes very enlarged (dilated).
Next: What are the symptoms of achalasia? »
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