I personally wouldn't. I don't see most things like diabetes, krohns, etc. as things to be shared. I suppose that if you are concerned that it may be cause for an unusual number of absences (for example if you have a suppressed immune system and are therefore susceptible to every bug that comes down the pipeline) it might be worth sharing. Although, that may be best shared after you are in school and only when it occurs. I think that I would consider my audience, too. For example, applying to grad school in counseling would lead me to believe that my professors go to bat for people who have greater odds than most and have some knowledge of illness and how it affects students. A professor of say, economics, might have a more narrow perception of your illness and only have personal biases to draw an opinion from.

In truth, you have made it this far. You have what it takes.

I think of answers to special circumstances to be more along the lines of.........

......I withdrew from class x in spring of 07 and my grades fell in other courses during this same semester because of the death of my mother.........
or
.....I did not do well in semester X because I was hospitalized with ............

I think they are looking for answers to your "academic record", and not specifically illness.

Good Luck!