What Causes Discoloration On Back, Buttocks And Thighs?

I have had a discoloration on my back, buttock, thighs for a couple of years. It has a lacy purplish appearance and is not really bothersome except it stings from time to time and I do tend to break out in hives in these areas. I thought it was livedo reticularis but my dermatologist did a biopsy that diagnosed it as reticular erythematous mucinosis. I was diagnosed with FMS and CFS about 12 years ago. I guess I and wondering if REM is associated with lupus and exactly what REM is.