Rheumatoid arthritis (RA) and psoriatic arthritis (PsA) are both inflammatory, autoimmune conditions. The symptoms of rheumatoid arthritis and psoriatic arthritis are similar, including joint stiffness, pain, and inflammation, as well as fatigue. Rheumatoid arthritis is the most common type of inflammatory arthritis, affecting more than 1 million people in the United States. RA occurs when the immune system attacks the body’s own tissue instead of bacteria and viruses. This inflammation causes permanent joint damage.
Psoriatic arthritis is less common than rheumatoid arthritis, but like RA, it occurs when the immune system attacks joint tissues. However, unlike RA, psoriatic arthritis is connected to another autoimmune condition called psoriasis. Psoriasis is an autoimmune disease that causes scaly, red patches to appear on the skin. These patches can burn or itch.
What Causes Rheumatoid Arthritis and Psoriatic Arthritis?
The exact cause of rheumatoid arthritis is unknown, although scientists believe that environmental factors — such as smoking, pollution, or infections — and genetic issues trigger the autoimmune response. If you have a family history of RA, you are more likely to develop it as well.
Most people who develop psoriatic arthritis show the skin symptoms of psoriasis first, although some people experience PsA without ever having psoriasis symptoms. About 30 percent of people who have psoriasis will eventually go on to develop PsA. The severity of psoriasis symptoms is not linked to the severity of PsA symptoms. A person with both could have severe psoriasis skin lesions and mild PsA symptoms, or mild skin lesions but severe PsA joint pain.
Both rheumatoid arthritis and psoriatic arthritis cause similar joint symptoms. The affected joints are painful and stiff, and feel swollen and hot. However, RA and PsA tend to show up in different joints. For example, they affect different parts of the spine. RA often causes problems in the cervical spine in the neck. Up to 80 percent of people with RA report experiencing neck pain. PsA often causes a condition called spondylitis, which causes lower back pain. Spondylitis involves inflammation in the joints of the spine and between the spine and pelvis. Up to half of people with PsA will experience spondylitis pain.
RA is also more likely to affect the hands, such as the joints in the wrists and fingers, while PsA is more likely to affect the feet. RA and PsA affect different small joints within fingers and toes. RA affects the joints closest to the hands and feet and the middle finger and toe joints, while PsA attacks the joints closest to the nail bed. People with PsA can experience a condition called dactylitis, in which the fingers or toes swell up and resemble sausages. Dactylitis is often the first symptom of PsA, and it may be the only joint symptom for several years. PsA even affects the nails themselves. People with PsA often have pitted, ridged nails, which appear similar to nails with a fungal infection.
Another difference is that RA tends to cause symmetrical joint pain and stiffness, meaning that the same joints on both sides of the body are affected. For example, with RA, both knees will be affected, or both wrists. PsA is more likely to be asymmetric, so both joints aren’t necessarily involved.
Imaging, such as X-rays and magnetic resonance imaging (MRI), is useful in diagnosing both RA and PsA, as well as learning how far the disease has advanced. X-rays are the first line of diagnosis for both conditions, as they are inexpensive and easy to reproduce. More sensitive technologies, like MRI, are more expensive and therefore used as second-line diagnostic tools. RA and PsA can produce different patterns of inflammation, and ultrasound can be useful in detecting these patterns and getting a definitive diagnosis.
Blood tests can also help tell the difference between RA and PsA. About 80 percent of people with RA are said to have seropositive RA, which means they test positive for rheumatoid factor (RF) or for cyclic citrullinated peptide (CCP) antibodies. In contrast, most people with PsA will not have RF or CCP antibodies and be considered seronegative. However, it is also possible to have seronegative RA.
Many of the same treatment options are used to treat both RA and PsA. Nonsteroidal anti-inflammatory drugs (NSAIDs), such as aspirin and Ibuprofen, are useful for over-the-counter treatment of both conditions. Corticosteroid injections can provide quick relief for RA and PsA symptoms. Side effects associated with steroid use, and with oral steroids especially, mean these medications are not a good long-term option for treating joint pain. In addition, corticosteroid use can make psoriasis flare-ups more volatile in people who have PsA.
Methotrexate, a disease-modifying antirheumatic drug (DMARD), is the most commonly used DMARD for RA. Methotrexate is sometimes prescribed off-label for PsA. However, it is not as effective for PsA as it is for RA.
Biological DMARDs, such as Enbrel (Etanercept), Remicade (Infliximab), Humira (Adalimumab), Simponi (Golimumab), and Cimzia (Certolizumab pegol) are approved by the U.S. Food and Drug Administration (FDA) for moderate to severe RA and for PsA. Some of these drugs may be administered along with Methotrexate. Unlike Methotrexate, biological DMARDs have been shown to be effective in preventing bone erosion in people with PsA, making these drugs especially helpful.
Immunomodulators, drugs like Orencia (Abatacept), that affect the immune responses that cause inflammation, are also effective for both RA and PsA. Xeljanz (Tofacitinib) is another immunomodulator that works for RA and PsA. It is FDA approved for people with RA who have not responded well to or cannot tolerate Methotrexate and for people with PsA who have not responded well to or cannot tolerate Methotrexate or other DMARDs.
Because of cellular differences between RA and PsA, some drugs are effective for one disease and not the other. People with PsA have high levels of inflammation-causing proteins called interleukins, specifically IL-17A and IL-12/23. The IL-17A inhibitor drugs Cosentyx (Secukinumab) and Taltz (Ixekizumab) and the IL-12/23 drugs Stelara (Ustekinumab) and Tremfya (Guselkumab) help block the production of these proteins, reducing inflammation. These drugs do not help treat RA.
Inflammation in RA is associated with a different interleukin called IL-6. The IL-6 inhibitor drugs Actemra (Tocilizumab) and Kevzara (Sarilumab) work against RA, but have not been proven to help with PsA.
It’s technically possible to have both RA and PsA. It’s also possible to have an atypical case of just one of the conditions, so talk to your doctor if you are confused about your symptoms. Some people with PsA never experience the obvious skin disease symptoms of psoriasis, making it easy to confuse PsA with RA. As scientists learn more about the specific causes of each condition, it’s likely that diagnoses and treatments will become more precise.
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