What Is The Recurring Dark Itchy Patch On The Calf?

My 4 year old has a dark itchy patch on his calf, the size f a dime, that is itchy. It gets irritated & bleeds when he scratches it. Antifungal cream seems to resolve it temporarily, but it comes back. He has had ti for over a year now & his pediatrician said 'ringworm', but it hasn't spread to his sister or his parents - and it is always on the calf of his right leg.