Not much. Many people have anal itch. It isn't a precursor of anything. If that's what your doctors diagnosed, that's most likely what it is. Diarrhea of whatever cause makes it worse, but it isn't part of the colitis or anything else internal. Treatment creams plus gentle washing and moisturizing holds it in check.
Best.
Dr. Rockoff
if so, probably candida / yeast, a virulent form, little can be done except long term treatment w/ drying powder.
However, if it is an overgrowth of yeast in the 'gut'/ gastrointestinal lining, than, a product called three lac, may solve the problem - and you'd be a lucky person at that.