Psoriatic arthritis (PsA) and osteoarthritis (OA) are two types of arthritis. Both affect the joints and produce symptoms such as stiffness, swelling, and pain. However, PsA is primarily an inflammatory autoimmune condition (like rheumatoid arthritis), while OA is caused by mechanical wear on the joint itself.
Because of the similarities between PsA and OA — and because results of imaging and blood tests are not always clear — the diagnostic process can be a challenge. Some people living with one type may even be misdiagnosed with the other, like one MyPsoriasisTeam member who wrote, “It turned out that I didn’t have osteoarthritis, but psoriatic arthritis was the culprit.” This can cause confusion when it comes to finding an effective treatment.
Here’s what people need to know about PsA and OA, including the key differences between their symptoms, causes, and treatments.
PsA occurs when the immune system mistakenly attacks the body’s own healthy tissues instead of foreign invaders, like viruses and bacteria. PsA is related to psoriasis, an autoimmune disease distinguished by scaly patches on the skin that can burn or itch.
Osteoarthritis is a condition in which cartilage — the cushiony layer between the joints — wears away over time. Bones begin to rub against each other, causing pain, crunching or grinding, and shape changes in the joints. Mild inflammation may occur in OA, but this is not characteristic of the condition and does not come from immune system issues.
Most people who develop PsA experience the skin symptoms first, although some individuals with PsA never have psoriasis symptoms. In the United States, about 30 percent of people with psoriasis eventually develop PsA.
The severity of a person’s psoriasis symptoms is not linked to the severity of their PsA symptoms. Some people may have severe skin lesions but mild PsA symptoms, and others may have mild lesions but severe joint pain.
Both people with PsA and those with OA will experience joint pain. However, differences in the pain can help differentiate between the two conditions.
Pain from PsA tends to come and go, flaring up and then settling down as inflammation waxes and wanes. OA pain usually comes on slowly over the course of years. As the cartilage wears down, it becomes more painful to use that joint.
Although both people with both types of arthritis will feel stiff, the patterns differ. Those with PsA tend to experience more extreme stiffness that affects several areas of the body. It may disappear with movement and as the day goes on. Those with OA may wake up with specific joints that are stiff or experience bouts throughout the day, but the stiffness usually goes away within about 30 minutes.
Stiffness in OA, in particular, tends to be tied to overuse of the joints. When a person with OA uses a joint, it hurts. If they use it too much, the joint may become swollen and painful, although those symptoms should ease with rest. For people with PsA, use may make a stiff joint feel better and usually won’t worsen symptoms. Ultimately, joint use is not tied to pain and swelling in PsA as it is with OA.
People with either PsA or OA may develop bony growths called bone spurs in their joints over time, which can make it hard to pinpoint which type of arthritis a person has.
One joint symptom that is not shared with both conditions is unusual sounds, like crunching or grinding, that people with OA may experience. Referred to as crepitus, noisy joints do not occur with PsA.
Because PsA is a systemic disease, it can cause a slew of symptoms not seen in those with OA. PsA may also cause:
PsA and OA differ distinctly in their causes.
Aging and wear and tear on the joints lead to OA. Layers of protection inside the joints break down, causing bones to rub against one another. This friction causes pain and can change the shape of the joint over time. People who overuse a specific joint or set of joints for their work or in sports are more likely to end up with OA and develop it earlier. Injury to a joint may also eventually cause OA.
The exact mechanism of how the joint breaks down is unknown. More research is needed to understand exactly how, why, and when this happens, as well as why it occurs in some people but not others.
The cause of PsA is not understood. However, rheumatologists and researchers believe that a combination of biological (genetic) and environmental factors can trigger the onset of PsA.
Beyond closely assessing pain and swelling patterns, there are a few ways that a doctor or rheumatology expert can differentiate between PsA and OA.
Imaging tests, such as X-rays and MRI, can help with diagnosing both PsA and OA and determining how far the disease has advanced.
X-rays are the first line of diagnosis for both conditions. More sensitive technologies, like MRI, cost more and are therefore used as second-line diagnostic tools.
Ultrasound imagery can be useful in recognizing specific inflammatory patterns that occur in PsA. These may be ordered if other test results are inconclusive.
Blood tests can help identify inflammatory markers such as rheumatoid factor and cyclic citrullinated peptide antibodies. These markers indicate rheumatoid arthritis. Testing for these factors can help your doctor pinpoint the cause of your joint pain or perhaps rule out other health conditions with similar symptoms. OA does not have markers that show up on blood tests.
Looking at the fluid in the joints can help confirm a diagnosis of PsA. Your rheumatologist will remove a bit of the affected joint’s fluid, which will be analyzed for clues to the cause of your joint pain.
Some treatment options for PsA and OA overlap, whereas others are specific to one of the two conditions.
Over-the-counter nonsteroidal anti-inflammatory drugs (NSAIDs), such as aspirin and ibuprofen, can help manage mild to moderate symptoms of both PsA and OA. These drugs help reduce pain, inflammation, and swelling.
Corticosteroids injected into the affected joint can provide quick relief for PsA and OA symptoms. However, because of the side effects associated with steroid injections and other steroid use (oral steroids, in particular), these medications are not a good long-term option for treating joint pain.
Disease-modifying antirheumatic drugs (DMARDs) have been proved in clinical studies to stop or slow disease progression in people with inflammatory arthritis. Methotrexate (sold as Otrexup, Rasuvo, and Trexall) is one of the most commonly prescribed medications in this category. Biologic DMARDs, such as etanercept (Enbrel), infliximab (Remicade), and adalimumab (Humira), are approved by the U.S. Food and Drug Administration (FDA) for PsA. Some of these drugs may be taken along with methotrexate.
Biologic DMARDs may be given for severe cases of PsA or when other drugs haven’t worked. Drugs in this class are not usually used to treat OA. Similarly, immunomodulators like abatacept (Orencia) and tofacitinib (Xeljanz), which target specific immune responses that cause joint inflammation, can be effective for PsA but not OA.
People diagnosed with PsA and OA often benefit from both physical and occupational therapy. Physical therapists can help develop exercise plans that won’t make your arthritis symptoms feel worse. Certain exercises may also help boost flexibility and ease stiffness and joint pain.
Occupational therapists can help you make lifestyle changes so you can go through your daily activities without further damaging joints or experiencing pain.
You can have PsA and OA at the same time and in the same joints. One member experienced both conditions at once, sharing that they “also have osteoarthritis and fibromyalgia” alongside PsA.
If you think you are dealing with PsA, OA, or both, it’s important to see a health care provider soon. They can help you through the diagnostic process and then work with you to find a treatment plan that will be effective and work for your body.
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Do you live with PsA and wonder if you have OA, too? Maybe you have been diagnosed with both conditions, and you’re learning how to live with them. Share your thoughts or questions in the comments below or by posting on your Activities page.