What Causes Purple Spots On Palms Of Hands And Feet?

My 13 yr old son has purplish spots on the palms of his hands and his feet, that come and go frequently. They don't itch or hurt. He also has alot of headaches and says the room sometimes goes gray when he stands up. He has had a cat scan, normal, blood work, normal and eye exam, normal. What could this be?