Melanosis coli, also pseudomelanosis coli, is a disorder of pigmentation of the wall of the colon

Colon (anatomy)

The colon is the last part of the digestive system in most vertebrates; it extracts water and salt from solid wastes before they are eliminated from the body, and is the site in which flora-aided fermentation of unabsorbed material occurs. Unlike the small intestine, the colon does not play a...

, often identified at the time of colonoscopy

Colonoscopy

Colonoscopy is the endoscopic examination of the large bowel and the distal part of the small bowel with a CCD camera or a fiber optic camera on a flexible tube passed through the anus. It may provide a visual diagnosis and grants the opportunity for biopsy or removal of suspected...

. It is benign, and may have no significant correlation with disease. The brown pigment is lipofuscin

Lipofuscin

Lipofuscin is the name given to finely granular yellow-brown pigment granules composed of lipid-containing residues of lysosomal digestion. It is considered one of the aging or "wear-and-tear" pigments, found in the liver, kidney, heart muscle, adrenals, nerve cells, and ganglion cells...

 in macrophage

Macrophage

Macrophages are cells produced by the differentiation of monocytes in tissues. Human macrophages are about in diameter. Monocytes and macrophages are phagocytes. Macrophages function in both non-specific defense as well as help initiate specific defense mechanisms of vertebrate animals...

s, not melanin

Melanin

Melanin is a pigment that is ubiquitous in nature, being found in most organisms . In animals melanin pigments are derivatives of the amino acid tyrosine. The most common form of biological melanin is eumelanin, a brown-black polymer of dihydroxyindole carboxylic acids, and their reduced forms...

.

Etiology

The most common cause of melanosis coli is the extended use of laxative

Laxative

Laxatives are foods, compounds, or drugs taken to induce bowel movements or to loosen the stool, most often taken to treat constipation. Certain stimulant, lubricant, and saline laxatives are used to evacuate the colon for rectal and/or bowel examinations, and may be supplemented by enemas under...

s, and commonly anthraquinone

Anthraquinone

Anthraquinone, also called anthracenedione or dioxoanthracene is an aromatic organic compound with formula . Several isomers are possible, each of which can be viewed as a quinone derivative...

 containing laxatives such as Senna and other plant glycosides. However, other causes are identified, including an increase in colonic epithelial apoptosis

Apoptosis

Apoptosis is the process of programmed cell death that may occur in multicellular organisms. Biochemical events lead to characteristic cell changes and death. These changes include blebbing, cell shrinkage, nuclear fragmentation, chromatin condensation, and chromosomal DNA fragmentation...

. Endoscopically

Endoscopy

Endoscopy means looking inside and typically refers to looking inside the body for medical reasons using an endoscope , an instrument used to examine the interior of a hollow organ or cavity of the body. Unlike most other medical imaging devices, endoscopes are inserted directly into the organ...

, the mucosa

Mucous membrane

The mucous membranes are linings of mostly endodermal origin, covered in epithelium, which are involved in absorption and secretion. They line cavities that are exposed to the external environment and internal organs...

 may show a brownish discoloration in a moire pattern

Moiré pattern

In physics, a moiré pattern is an interference pattern created, for example, when two grids are overlaid at an angle, or when they have slightly different mesh sizes.- Etymology :...

.

Histologic appearance

On biopsy

Biopsy

A biopsy is a medical test involving sampling of cells or tissues for examination. It is the medical removal of tissue from a living subject to determine the presence or extent of a disease. The tissue is generally examined under a microscope by a pathologist, and can also be analyzed chemically...

, melanosis coli shows characteristic pigment-laden macrophage

Macrophage

Macrophages are cells produced by the differentiation of monocytes in tissues. Human macrophages are about in diameter. Monocytes and macrophages are phagocytes. Macrophages function in both non-specific defense as well as help initiate specific defense mechanisms of vertebrate animals...

s within the mucosa on PAS

Periodic acid-Schiff

Periodic acid-Schiff is a staining method used to detect glycogen and other polysaccharides in tissues. The reaction of periodic acid oxidizes the diol functional groups in glucose and other sugars, creating aldehydes that react with the Schiff reagent to give a purple-magenta color...

 staining.

The histologic differential diagnosis

Differential diagnosis

A differential diagnosis is a systematic diagnostic method used to identify the presence of an entity where multiple alternatives are possible , and may also refer to any of the included candidate alternatives A differential diagnosis (sometimes abbreviated DDx, ddx, DD, D/Dx, or ΔΔ) is a...

 of mucosal pigmentation is: lipofuscin (melanosis coli), hemosiderin-laden macrophages, and melanin

Melanin

Melanin is a pigment that is ubiquitous in nature, being found in most organisms . In animals melanin pigments are derivatives of the amino acid tyrosine. The most common form of biological melanin is eumelanin, a brown-black polymer of dihydroxyindole carboxylic acids, and their reduced forms...

 (rare).

Relation to true melanoses

The condition is unrelated to true melanoses, such as Peutz-Jeghers syndrome

Peutz-Jeghers syndrome

Peutz–Jeghers syndrome, also known as hereditary intestinal polyposis syndrome, is an autosomal dominant genetic disease characterized by the development of benign hamartomatous polyps in the gastrointestinal tract and hyperpigmented macules on the lips and oral mucosa...

 and smoker's melanosis

Smoker's melanosis

Smoker's melanosis is characterized by flat, irregular hyperpigmentation of the connective tissue underlying the oral mucosa resulting from tobacco smoking. Basal cells and macrophages in the underlying connective tissue contain unusual amounts of melanin, which creates the darker pigmentation...

.

Peutz-Jegher syndrome causes pigmentation of the skin and mucous surfaces with melanin

Melanin

Melanin is a pigment that is ubiquitous in nature, being found in most organisms . In animals melanin pigments are derivatives of the amino acid tyrosine. The most common form of biological melanin is eumelanin, a brown-black polymer of dihydroxyindole carboxylic acids, and their reduced forms...

, and polyps in the digestive tract.

Non-colonic pseudomelanoses

Pseudomelanoses of other parts of the gastrointestinal tract have also been reported, and are of unclear relevance.

Patients with colostomies

Colostomy

A colostomy is a surgical procedure in which a stoma is formed by drawing the healthy end of the large intestine or colon through an incision in the anterior abdominal wall and suturing it into place. This opening, in conjunction with the attached stoma appliance, provides an alternative channel...

 can have melanosis involving the stoma

Stoma (medicine)

A stoma is an opening , either natural or surgically created, which connects a portion of the body cavity to the outside environment...

, which is also of no significance.

External links

• Endoscopic video of Melanosis coli, via the DAVE Project