What Causes Severe Pain In Legs And Feet With Black Discoloration On Knuckles?

A year ago I had knuckles that turned bright red anfd burned like crazy. It came and went but it would appear regularly. it stopped at some point and now it is back. I also have severe pain in my legs and feet because of lower lumbar disc bulges and some other things as well. I have MS and was tested for Rheumatoid arthritis. It was negetive. Should I be tested again?