If you've been feeling aches and pains that just won't go away, it could be time to see a rheumatologist. A rheumatologist is a medical doctor who specializes in diseases of the joints and muscles, as well as autoimmune diseases. They diagnose and treat arthritis, gout, and autoimmune diseases. Here's what you need to know about what a rheumatologist does and how they can help you. What Conditions Does a Rheumatologist Treat?