I think that's a great topic! (:
A good way to approach it would be to describe briefly your condition and how it has negatively impacted your life. Then spend the bulk of your essay showing how you've managed to work around this condition to accomplish certain things that you would not have been able to without a certain amount of dedication and hard work. Then wrap up by saying how your condition has inspired you to study medicine in the hopes of helping others who are going through the same thing as you.
Don't subscribe directly to this of course, it's just a rough outline and the essay should come from you to be as personal as possible.
Good luck with your essay!
If you could help me with choosing a topic, that would be fantastic! (Help with Supplement essay! (will help you back :D )