Your doctor will do a physical exam and ask you about your past health and symptoms to diagnose polymyalgia rheumatica (PMR) and giant cell arteritis (GCA). Because the two conditions often occur together, it is important that your doctor determine which one is causing your symptoms, as giant cell arteritis can be serious and needs immediate treatment with higher doses of medicine than polymyalgia rheumatica does.

Age is an important factor in making the diagnosis, because these conditions rarely occur in people younger than 50. A limited range of motion in the arms may be a sign of polymyalgia rheumatica, and arteries on the temple or forehead that are swollen, lumpy feeling, or tender may be a sign of giant cell arteritis.

Tests that can help diagnose polymyalgia rheumatica and giant cell arteritis include:

• Erythrocyte sedimentation rate (ESR). This test measures how quickly red blood cells (erythrocytes) settle in a test tube in 1 hour. A high ESR may be a sign of polymyalgia rheumatica or giant cell arteritis.
• Complete blood count (CBC). People with either polymyalgia rheumatica or giant cell arteritis often have mild anemia. A CBC can show this.
• C-reactive protein. This test measures the amount of C-reactive protein (CRP) produced when you have inflammation somewhere in your body. Both giant cell arteritis and polymyalgia rheumatica can cause a high CRP level.
• Temporal artery biopsy. When your doctor suspects giant cell arteritis, this test can confirm the condition. In this biopsy, a surgeon will take a sample of a blood vessel on your temple and test it for inflammation.
• Ultrasound. In some cases, ultrasound of the arteries on the side of the face near the temple (temporal arteries) may help diagnose giant cell arteritis. This way of using ultrasound is still being studied for use in the United States.
• Arteriogram, CT scan, and magnetic resonance angiogram. These tests are done if giant cell arteritis is suspected in parts of your body other than your head. In rare cases, giant cell arteritis may affect arteries leading to the arms or heart.

Your doctor may confirm a diagnosis of polymyalgia rheumatica with a trial of corticosteroid medicine. If you have polymyalgia rheumatica, you are very likely to have great relief of symptoms within 2 to 4 days of starting treatment.

Tests that may be done to be sure another condition is not causing your symptoms include:

• Rheumatoid factor (RF) test, to check for rheumatoid arthritis.
• Antinuclear antibodies test, to check for lupus or another autoimmune disease.
• Thyroid-stimulating hormone test, to check for an underactive thyroid gland (hypothyroidism).
• Serum protein electrophoresis (SPE or SPEP) test to check for abnormal proteins found in diseases like multiple myeloma.