Sometimes it can be hard to figure out just what’s causing your joint pain. Take rheumatoid arthritis (RA) and polymyalgia rheumatica (PMR): Both of these autoimmune diseases cause inflammation, swelling, and pain. However, they also have key differences, and being aware of these distinctions can help lead to the right diagnosis — and the best treatment for you.

In rheumatoid arthritis, the immune system attacks the lining of the joints in episodes called flares. During an RA flare, the affected joints become painful and swollen. The inflammation can also cause fever, exhaustion, and weakness. Over time, repeated inflammation can cause joint changes that make movement difficult. RA can also affect other parts of the body, like the lungs, heart, and eyes.

Polymyalgia rheumatica is an inflammatory condition that arises from problems with the immune system. PMR causes muscle pain along with stiffness in the joints and surrounding tissues. It can also lead to fatigue, fever, weight loss, weakness, and other symptoms. Morning stiffness is common and may resolve as the day goes on. PMR often affects the entire body and can make it hard to raise your arms above your shoulders.

Read more to learn about five differences between polymyalgia rheumatica and rheumatoid arthritis that help health care providers distinguish between them and diagnose each condition.

1. Which Body Areas They Affect

The biggest difference between polymyalgia rheumatica and rheumatoid arthritis is which parts of the body they involve. Most people with PMR experience stiffness and pain in their neck and shoulders and their buttocks, hips, and thighs. “The upper body stiffness doesn't change,” one myRAteam member said about PMR. This soreness is usually symmetrical — it occurs on both sides of the body at the same time.

PMR doesn’t usually cause joint swelling or damage. When synovitis, or joint inflammation, does occur, it’s usually mild. Instead, people with PMR experience bursitis (inflammation of the bursas, fluid-filled sacs in the joints) and tendinitis (inflammation of tendons, cords that connect muscle to bone and help joints move smoothly).

Unlike people with PMR, people with RA experience flares of inflammation in multiple joints. Usually, the inflammation affects joints in the limbs — knees, ankles, shoulders, elbows, wrists, and the small joints in the hands.

Unlike PMR, RA doesn’t always occur in joints on both sides of the body. Early-stage RA can affect just one side, with symmetrical joint involvement suggesting that the disease has progressed.

2. When They’re Diagnosed

Rheumatoid arthritis occurs among younger people compared with polymyalgia rheumatica. PMR almost always arises after age 50, whereas RA typically occurs in 30- to 50-year-olds. However, RA can also develop at older ages and be more challenging to diagnose.

3. How Long Episodes Last

Polymyalgia rheumatica comes on much more suddenly than rheumatoid arthritis does. People with RA often experience shorter episodes of pain that come and go over the course of months. PMR pain is more persistent, and untreated symptoms can last for years without letting up.

4. What Conditions Are Related to Them

According to the journal Practical Pain Management, about 10 percent to 20 percent of people with polymyalgia rheumatica will also develop giant cell arteritis, a condition that isn’t associated with RA. Giant cell arteritis causes vasculitis (inflammation within the arteries) and usually affects the arteries in the head, near the temples.

Symptoms of giant cell arteritis include:

• Severe pain around the temples
• Tenderness of the head and scalp
• Jaw pain when chewing or opening the mouth
• Vision loss
• Double vision

It’s important to be alert to these symptoms and see your health care provider promptly. Left untreated, inflammation caused by giant cell arteritis can cause permanent blindness.

Rheumatoid arthritis mainly involves the joints but also is associated with many conditions that affect other organs. These extra-articular (outside the joints) conditions and symptoms include:

• Dry eyes
• Dry mouth
• Pleural effusion (fluid buildup in tissue around lungs, sometimes called “water on the lungs”)
• Lung nodules (abnormal growths that usually aren’t cancerous)
• Kidney problems
• Anemia (low red blood cells)
• Leukemia and lymphoma (types of blood cancer)

Up to 20 percent of people with RA develop subcutaneous nodules (swollen lumps under the skin), usually near affected joints. Subcutaneous nodules don’t tend to be tender or painful, but they can be unsightly and affect joint function. People with PMR don’t get subcutaneous nodules.

5. How They’re Treated

Polymyalgia rheumatica and rheumatoid arthritis call for different treatment regimens. Both conditions may be treated with corticosteroids — medications that reduce inflammation — but unlike RA, PMR often responds very well to low doses. The symptom relief that people with PMR feel after treatment with low-dose prednisone (a type of corticosteroid) is often so dramatic that it confirms the diagnosis.

Corticosteroids can be part of an RA treatment regimen, but disease-modifying antirheumatic drugs (DMARDs) like methotrexate, biologics, and Janus kinase (JAK) inhibitors are also used to treat symptoms and help slow disease progression. Corticosteroids may help control pain and inflammation until DMARDs or other types of RA drugs start to work.

Similarities Between Polymyalgia Rheumatica and Rheumatoid Arthritis

Polymyalgia rheumatica and rheumatoid arthritis do share some aspects beyond symptoms like musculoskeletal pain. For example, both conditions occur in women more than men and seem to be more common among people of European descent.

As a myRAteam member noted, “My symptoms are like RA, but I’ve been diagnosed with polymyalgia.” The similarities can make it hard to tell the two conditions apart.

In addition, blood testing doesn’t necessarily confirm either diagnosis. Blood tests for erythrocyte sedimentation rate and high levels of C-reactive protein detect inflammation but can’t distinguish between PMR and RA. Tests for cyclic citrullinated peptide antibodies and rheumatoid factor can help confirm an RA diagnosis, but not every person with RA tests positive — so you could have a negative test and still have either condition.

An RA diagnosis depends on the presence of inflammation within the joints, which can be confirmed in the clinic or through imaging tests such as ultrasound or MRI. PMR, on the other hand, results from inflammation in the structures that surround the joints and shows up on ultrasound, MRI, or PET scan images.

Differences in symptoms — and how those symptoms respond to different treatments — can make it easier for a trained health care provider to distinguish between PMR and RA. A visit to a rheumatologist can help you get the right diagnosis, as one myRAteam member reported: “I was diagnosed with PMR. My attending physician said I had RA. Thank God I went to a rheumatologist!”

Talk With Others Who Understand

On myRAteam is the social network for people with rheumatoid arthritis and their loved ones, more than 203,000 members come together to ask questions, give advice, and share their stories with others who understand life with RA.

Have you been diagnosed with polymyalgia rheumatica or RA? Was it difficult to figure out which condition you have? Share your experience in the comments below, or start a conversation by posting on your Activities page.