Rheumatoid arthritis is a serious autoimmune disease that attacks the joints and other body parts. But RA can be tough to diagnose. Symptoms can mimic other illnesses, or they may flare, then fade, only to flare again somewhere else. Lab tests aren’t perfect—you can test negative for RA factors and still have it. And X-rays don’t show signs until later on. Here are some tricky rheumatoid arthritis symptoms and hints that they’re due to RA and not some other condition.