Tests and diagnosis
The signs and symptoms of polymyalgia rheumatica are similar to those of a number of other conditions, including rheumatoid arthritis and polymyositis — a disease that causes muscle inflammation and weakness. For that reason, your doctor will want to rule out other possible causes for your pain and stiffness before making a diagnosis of polymyalgia rheumatica.
To aid in the diagnosis, your doctor will interview you about your medical history and current symptoms and conduct a thorough physical exam. You're also likely to have one or more tests, including:
- Sed rate. If your doctor suspects polymyalgia rheumatica, he or she will order a blood test that checks your erythrocyte sedimentation rate, commonly known as the sed rate. This test measures how quickly your red blood cells settle when placed in a test tube. Generally, the blood cells fall faster — that is, the sed rate increases — when inflammation is present. But because many conditions can cause inflammation in your body, including infections and chronic diseases, such as rheumatoid arthritis and other rheumatic disorders, an elevated sed rate alone can't confirm the presence of polymyalgia rheumatica.
- Rheumatoid factor (RF). RF is an antibody — a protein made by the immune system — that's often present in the blood of people with rheumatoid arthritis, but not in the blood of people with polymyalgia rheumatica. Consequently, this test can help your doctor distinguish between the two conditions.
Other blood tests. Your doctor may also check the number of red blood cells and platelets (thrombocytes) in your blood. Platelets are colorless blood cells that help stop blood loss when you're injured. Most people with polymyalgia rheumatica have an unusually high number of these cells (thrombocytosis). On the other hand, many people with polymyalgia rheumatica have a lower number of red blood cells than normal and are often anemic.
You may also have a simple and inexpensive blood test that checks levels of C-reactive protein in your blood. The protein is produced by your liver as part of a normal immune system response to injury or infection. Among other things, high blood levels of C-reactive protein may indicate the presence of inflammation.
Checking for giant cell arteritis
If you receive a diagnosis of polymyalgia rheumatica, your doctor will check for a related condition called giant cell arteritis, which occurs in some people with polymyalgia rheumatica. Signs and symptoms — such as new headaches, a tender scalp, pain when you chew, visual changes including double vision or visual loss — along with the results of a sed rate test can help determine whether you have this disorder.
The only way to confirm a diagnosis of giant cell arteritis is by taking a small sample (biopsy) from the scalp artery in your temple (temporal artery). The sample is then examined under a microscope in a laboratory. Although polymyalgia rheumatica and giant cell arteritis are both treated with corticosteroids, the recommended dosage for management of giant cell arteritis is higher than for polymyalgia rheumatica. As a result, your doctor will likely recommend confirming the diagnosis of giant cell arteritis with a biopsy.