I have had a “birthmark” on my right ankle since

Patient: I have had a “birthmark” on my right ankle since I was nearly 1 year old. My mother thought it was spots of dirt on my foot and tried to clean it for more than enough time to realize it was permanent. So she took me to my pediatrician and was told it was a bone disease that appeared as spots on the affected joints. I have very week wrists and ankles but no severe issues yet and I am 29. Can you tell me what this joint disease might be? I have searched all possible routes for an answer rather than simply asking a doc.. Soo, any ideas?

Doctor: