What Causes Itchy, Recurring Bruise On Back?

I have been noticing a re-occuring bruise in the middle of my back for about 4 years now. I told the doctor, and at the time. . .the bruise wasn't as visable. It comes and goes, sometimes dark, then lightens up. My skin gets real itchy in that same spot ,sometimes. I have always had back problems as I suffer from Anklosying Spondylitis, and Sculliosis. I have always gotten Chiropractic treatment, but have been afraid to allow the chiropractor to continue adjusting my back in that area. My doctor seems dis-interested. . . What do you think?

Thanks JJ