A medical professional who specializes in the diagnoses and treatments of rheumatic diseases, such as arthritis, vasculitis, and lupus: Rheumatologists have special interests in unexplained rashes, fevers, arthritides (plural form of arthritis), anemias, weaknesses, weight losses, fatigues, joint or muscle pains, autoimmune diseases, and anorexias. They often serve as consultants who function like researchers and diagnosticians for other doctors.