Melanosis Coli
(Pseudomelanosis
Coli)
Medical Author: Melissa C. Stoppler, MD
Medical Editor: Jay W. Marks, MD
What is melanosis coli?
Melanosis coli is a condition usually associated with
chronic laxative use in which dark pigment is deposited in
the lamina propria
(one of the lining layers) of the large intestine
(colon). The pigment deposition results in a characteristic dark brown to black
discoloration of the lining of the large intestine. This condition is sometimes called
pseudomelanosis coli because the pigment deposits consist of a pigment known as
lipofuscin and do not contain melanin as implied by the term "melanosis."
Lipofuscin is a cellular pigment that forms when cells are destroyed, often
called "wear and tear" pigment that can be found throughout the body.
The dark color of the intestinal lining may be uniform
or patterned, and the discoloration may be slight or very pronounced. The
intensity and pattern of the discoloration may even vary among different sites
in the colon of a patient. The condition may also be reversed upon
discontinuation of laxative use. In some cases, the wall of the colon appears
normal to the eye, but microscopic evaluation of biopsies by a pathologist reveals areas of pigment in
the colon's lining. The pigment in melanosis coli does not accumulate in polyps
or tumors of the large intestine.
What are the symptoms of melanosis coli?
Melanosis coli does not cause
symptoms.
What causes melanosis coli?
Melanosis coli usually results from chronic use
of laxatives of the anthranoid group. Some examples of anthranoid laxatives are
senna and rhubarb derivatives. Many of these laxatives have been in use for
hundreds of years. In 1997, the U.S. Food and Drug Administration (FDA) banned
the use of the popular anthranoid laxative phenolphthalein due to fears that it
might be carcinogenic (cancer-causing). Animal studies had shown that extremely
high doses of phenolphthalein led to tumors in animals, but it has never been
shown to cause cancers in humans.
The anthranoid laxatives pass through the gastrointestinal tract unabsorbed
until they reach the large intestine, where they are changed into their active
forms. The resulting active compounds cause damage to the cells in the lining of
the intestine and leads to apoptosis (a form of
cell death). The damaged (apoptotic) cells appear as darkly pigmented bodies that may be taken up by
scavenger cells known as macrophages. When enough cells have been damaged, the
characteristic pigmentation of the bowel wall develops.
Next: How is melanosis coli diagnosed? »
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