Jan 1, 2015 3 min read

DEAR DOCTOR K: My doctor suspects I have rheumatoid arthritis, but she wants to test me for several other disorders, including lupus and gout. Why?

DEAR READER: Several other diseases can cause symptoms and joint changes that are similar to rheumatoid arthritis (RA), including lupus and gout. That’s probably why your doctor is ordering the tests. She suspects you have RA, but she won’t know for sure unless she rules out these other diseases.

RA is an autoimmune disease. The body’s immune system attacks healthy tissue, primarily the tissue lining the joints. This causes swelling, pain, redness and stiffness in the joints. RA can affect other tissues throughout the body as well.

Accurately diagnosing RA, especially in the early stages, can be difficult. A physical exam, your symptoms, blood tests and imaging tests can all help. But before finalizing the diagnosis, your doctor may want to rule out other possibilities, including:

— LUPUS is an inflammatory autoimmune disease. Fever and joint pain are common early symptoms of lupus, just as they are for RA. The joints involved in lupus often are the same ones affected in RA. Lupus is diagnosed based on symptoms and laboratory tests.

— SCLERODERMA is an autoimmune disease that causes skin to thicken, tighten and look shiny. Some people have rheumatoid-like arthritis; others have a combination of arthritis and tightening of the tendons. People with scleroderma have certain antibodies in the blood that can be detected with a blood test.

— SJOGREN’S SYNDROME is also an autoimmune disease. Immune system cells tend to attack the tear and saliva glands, causing dry eyes and dry mouth. The disease may also cause joint pain and swelling that mimics RA. The diagnosis is made based on symptoms and the results of several tests.

— GOUT. This form of arthritis develops after tiny crystals of uric acid accumulate in joints, causing the joints to become swollen, red and very painful. It really hurts: I speak from experience as a doctor and a patient. Gout may be diagnosed by examining fluid from the joint under a microscope to see whether uric acid crystals are present. Blood tests may also be needed.

— PSEUDOGOUT is similar to gout, but results from deposits of certain kinds of crystals (made of calcium pyrophosphate) in joints. Long-standing pseudogout can resemble RA. Joint fluid may be examined under a microscope to verify the presence of calcium crystals. Blood tests may also be needed.

— OSTEOARTHRITIS. The joint pain of osteoarthritis can be similar to that caused by RA. However, there are significant differences between other symptoms and the causes of the two conditions.

In my experience, a diagnosis of RA is usually pretty straightforward. But before leaping to that diagnosis, a doctor should do the testing required to look for other causes of your joint symptoms — just as your doctor is doing.

(Dr. Komaroff is a physician and professor at Harvard Medical School. To send questions, go to AskDoctorK.com, or write: Ask Doctor K, 10 Shattuck St., Second Floor, Boston, MA 02115.)