Melanosis Coli

R. Fleischmann

■ Definition

Melanosis coli presents as dark brown pigmentation of the mucosa that may have a zebra-striped or reticulated appearance. The pigment, which is actually not melanin, but rather lipo-fuscin, is deposited extracellularly in macrophages. Because the pigment is not melanin, this phenomenon is also correctly called pseudomelanosis coli.

Clinical Picture

Pseudomelanosis Coli Leoparden

Fig. 15.2 Pseudo-melanosis coli.

Mosaiclike brown mucosal coloration. Tiny polyps usually remain lighter in color.

Fig. 15.2 Pseudo-melanosis coli.

Mosaiclike brown mucosal coloration. Tiny polyps usually remain lighter in color.

Melanosis coli is most often found in women with surreptitious heavy use of laxatives and who are seeking medical attention for chronic diarrhea. Low levels of potassium are often evident. The condition begins to reverse 12-18 months after laxative use is discontinued.

Diagnosis

, Sigmoidoscopy reveals dark pigmentation of the mucosa (Figs. 15.1, 15.2). Changes are most pronounced in the right hemicolon and cecum.

Endoscopic diagnostic criteria

► Dark pigmentation of the mucosa, from light brown to black, sometimes with a leopard-skin pattern.

► In advanced cases, the colon is dilated with loss of haustra.

► Tiny polyps and inflammatory mucosa often remain light against an otherwise dark background (Fig. 15.2). These should be biopsied.

Additional procedures. A colon contrast enema does not increase diagnostic yield.

Differential diagnosis. Melanosis coli is most often observed following use of anthracene (senna) laxatives, which are seldom prescribed nowadays. Phenolphthalein laxative use can be easily detected by using sodium hydroxide (alkalization causes the stool to turn red). Use of magnesium-containing laxatives can be determined by high magnesium stool content. Anthracene can also be detected in urine.

Treating laxative abuse is difficult as most patients deny misuse. Misuse of laxatives is often related to eating disorders, and both behaviors require psychotherapy.

■ Surveillance

Surveillance is not necessary, as melanosis coli has no malignant potential.

References

1. Hafter E. Praktische Gastroenterologie. 7th ed., Stuttgart: Thieme 1988; pp. 262-81.

Pseudomelanosis Coli

Pseudomelanosis coli. Brown, reticulated mucosal pattern (leopard-skin pattern).

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