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.
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