What Do Red, Spreading, Inflamed Bumps On Knees, Elbows And Wrists Suggest?

I had red bumps on my knees that were very inflamed and the next day they were on my elbows, wrists, and the backs of my knuckles. Dermatology in the hospital declared it as red it erythema nodosum. I was then told at my follow-up appt. that it would possibly be correct if it was only on my knees and legs, but since it appeared in other areas it is something else. After awhile the bumps turn to a deep bruising color. My joints are now aching... any thoughts would welcomed.