What Causes Dark Spots On The Arms?

I have had dark spots on both of my upper arms from 2007. I have been to dermatologist every where in my country who sat that I have atopic eczema. The medications they have given me have not helped at all. I bath with dove soap and do what was suggested by the dermatologist but a few months ago the reash has moved down below my elbow and around my elbow. What is this?