What is it??? -black pigment in colon


Marjorie Hagerty H.T. (ASCP) H.T.L., Q IHC at the Eisenhower Medical Center, 
Rancho Mirage, California asks:

>>We saw something today that we have not seen before. We had a colon with an 
incredible black pigment in the sub-mucosa. It is very black and abundant. 
Reminds me of carbon in the lung. Does not stain with Iron stain. Any ideas?<<

This spectacular blackening of the mucosal surface of the colon is called 
melanosis coli. It's caused by chronic ingestion of emodin (anthraquinone) 
cathartics such as senna, cascara sagrada, and aloe vera. (Some say the lowly 
prune contains a bit of emodin also.)

The pigment, supposedly arising in injured mitochondria, is found in 
macrophages in the lamina propria of the mucosa. It looks like melanin and to 
some degree stains like melanin, though on electron microscopy it clearly 
isn't melanin. Thus it stains with silver reducing (argyrophil) techniques 
such as Fontana- Masson, but does not stain as hemosiderin with the Perls 
prussian blue technique. It usually isn't acid-fast.

Only the colon is affected. Melanosis stops abruptly at the ileocecal valve. 
Sometimes the lymphoid nodules stand out like little white stars in a black 
sky. The obstructing cancer that causes the patient to take the laxative 
isn't colored either.

Emodin cathartics should be banned from commerce, but they're very popular 
with the herbal medicine people and are common ingredients of quack weight 
reducing formulas. Having a black colon doesn't do you any harm, but the 
cathartic eventually destroys the nerve cells of the myenteric plexus and 
then you REALLY get constipated.

Bob Richmond
Samurai Pathologist
Knoxville TN

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