Psoriatic arthritis (PsA) and ankylosing spondylitis (AS), one of the more common types of spondylitis, are both types of arthritis. Both are considered spondyloarthropathies, a family of chronic (ongoing) diseases of joints. They share some symptoms like joint pain, stiffness, and swelling. While AS is generally considered an axial type of arthritis (it affects the spine) and PsA is generally considered peripheral (it affects peripheral joints like hands and feet), their symptoms can overlap.
PsA often comes with the added burden of psoriasis, a skin condition that causes itchy and scaly patches. Meanwhile, AS primarily affects the spine, leading to stiffness and pain that can make it difficult to move around.
The fact that some people with PsA may experience back pain and some people with AS may experience psoriasis can make it difficult to tell when it’s PsA or AS. Diagnosing PsA or AS may take a long time, as they are often mistaken for other conditions or even for each other.
This article is intended to help people with PsA and their loved ones understand the similarities and key differences between PsA and AS. Although diagnosis of either condition requires a health care provider’s expertise, it can help to know what the key differences are. Distinguishing between PsA and AS is critical to getting the right treatment plan and preventing potential long-term issues such as further joint damage.
PsA is a type of arthritis that is linked to psoriasis, a skin and nail condition. Up to 3 in 10 people with psoriasis develop PsA. Per the National Psoriasis Foundation, for about 80 percent of people, PsA can start up to 10 years after they develop psoriasis. Others may have PsA without ever having (or noticing) psoriasis, although this is much less common (approximately 10 percent to 15 percent). PsA has several related conditions that can make living with PsA more difficult.
PsA is similar to rheumatoid arthritis in symptoms such as joint swelling, but it affects fewer joints. One form of arthritis that is linked to PsA is psoriatic spondylitis, which is arthritis of the lower back and spine. This form of arthritis overlaps with AS.
PsA can develop slowly or quickly, and symptoms can range from mild to severe. The severity of psoriasis and PsA are not totally related — you could have few skin issues but lots of joint pain and vice versa.
Common PsA symptoms include:
AS, also known as axial spondyloarthritis, is a type of spondylitis that causes inflammation in the spine and leads to back pain and stiffness. Spondylitis is an umbrella term for several types of arthritis that usually affect the spine. Other types of spondylitis include enteropathic arthritis, psoriatic arthritis, reactive arthritis, undifferentiated spondyloarthritis, peripheral spondyloarthritis, and juvenile spondyloarthritis.
Severe AS can lead to spinal bones fusing together, causing the spine to be rigid and difficult to bend. Bones in the chest may also fuse together.
Many people with AS experience mild back pain that comes and goes. Others experience more severe pain. AS mostly affects the back, but other joints can be involved, such as the shoulders, ribs, hips, knees, ankles, and feet.
Besides back pain, other AS symptoms include:
While PsA and AS have common symptoms and are thought to be related conditions, there are key differences in symptoms that help distinguish one from the other. Differences include whether there is back pain or skin and nail problems and where joint pain occurs.
One of the main distinguishing symptoms between AS and PsA is back pain. AS always affects the spine, causing back pain, whereas PsA more often causes pain in the peripheral joints.
For example, one MyPsoriasisTeam member with PsA wrote, “I get pain in almost all of my joints, but the worst pain is always in my left shoulder and left hip. … Other times, I get pain in my hands, wrists, elbows, knees, ankles, and sometimes a few toes.”
Another key difference in symptoms between PsA and AS is the presence of skin and nail issues. It’s common in people with PsA to have psoriasis and nail issues but rare for people with AS. Only about 10 percent of people with AS also have psoriasis.
The location of joint pain can also help distinguish between PsA and AS. For example, PsA usually causes joint pain in more peripheral joints such as fingers and toes. One MyPsoriasisTeam member talking about joint pain from PsA wrote, “I got joint pain all over my toes in my feet, my legs, and my hips.” If people with AS have peripheral joint pain, it’s usually in large, less peripheral joints such as the knees, hips, and shoulders.
While the exact cause of PsA is unknown, genes, immunity, and the environment may play a role. Some people may develop PsA after an injury.
Similarly, the exact cause of AS is unknown, though genes are also thought to play a role. The genetic marker HLA-B27 has been looked at for its association with the risk of developing AS, but research from Johns Hopkins shows it’s uncommon for people with the HLA-B27 gene to have AS — less than 5 percent of people with the gene also have AS, but estimates vary.
In addition, the link varies by race and ethnicity. Most white Americans with AS have the HLA-B27 gene, but only 50 percent of African Americans with AS have the gene.
Age is another risk factor for AS — most people develop symptoms before age 45, but the condition can occur in children and older adults as well. Other conditions may also increase the risk of AS. For example, people who may be more likely to develop AS are those with ulcerative colitis, Crohn’s disease, and psoriasis. AS may affect more young men than women, according to Johns Hopkins Medicine.
As both PsA and AS are arthritic conditions, diagnosis is best made by a rheumatologist. There is no single test for PsA or AS, so diagnosis may be a process of ruling out other conditions.
Diagnosing PsA and AS may include a family history, symptom assessment, physical exam, and lab tests. Lab tests can help rule out other inflammatory conditions like rheumatoid arthritis and gout. A health care provider may order X-rays to look at the condition of joints and an MRI or ultrasound if more information is needed.
Because the type and location of joint pain can differ between PsA and AS, a health care provider will likely ask about joint pain patterns. They may also look for skin and nail issues, which are common in PsA but not AS, or take a skin biopsy.
If a health care provider suspects that AS is present, they may also test for the genetic marker HLA-B27. The presence of this gene, along with other characteristic symptoms of AS, increases the chances of an AS diagnosis.
Treatment options for PsA and AS depend on your symptoms, age, and severity of disease activity. Although there is no cure for PsA or AS, certain medications can help treat the symptoms and slow progression of the condition. Some treatments overlap, but some medications are better for one condition than the other.
The earlier PsA is treated, the better it can help protect joints from further damage. Some medications that may be used to treat PsA include:
Other treatments may include lifestyle changes or nonmedical therapies. A health care provider might recommend the following nonmedical treatments to help manage PsA symptoms:
If PsA symptoms are severe, surgery may be recommended to replace or repair a damaged joint. One MyPsoriasisTeam member talking about their experience with PsA wrote, “I ended up having both hips and a reverse shoulder replacement last year, but these things can be prevented if caught in time. … I also see a physiotherapist who has given me exercises for my hips.”
Similar to treatment for PsA, AS treatments may include NSAIDs, biologics, or corticosteroids to reduce inflammation. Exercises to strengthen muscles, specifically back muscles, may also be recommended. Surgery is one of the advanced treatments for AS that may be needed in severe cases when a joint needs to be replaced or thickened or if hardened bone needs to be removed. Rods may also be placed in the spine.
Other AS treatments may include:
Always make sure to check with your health care provider or rheumatologist for how long certain medications should be taken, as some may only be recommended in the short term.
Because PsA and AS symptoms can overlap, it can be difficult to tell which of the conditions, or both, are present. For example, is AS with psoriasis the same thing as PsA? Research suggests it’s not.
People with PsA may have arthritis in the back or the sacroiliac joints in the pelvis, causing lower back pain. This is sometimes called axial psoriatic arthritis (axial PsA) — axial meaning involvement of the spine. For example, one MyPsoriasisTeam member talking about living with PsA wrote, “I’m newly diagnosed, but my arthritic pain is primarily in my lower back and hips.”
The presence of back pain with PsA has led some people to wonder if those with AS (where back pain is a key symptom) who also have psoriasis actually have PsA. Despite the overlap, research shows that these are two distinct conditions. People with AS and psoriasis are different from people with PsA in that they are more likely to have certain genetic markers and have back pain as their main symptom.
One way to think about it is that people with PsA can have back pain, but the arthritis pain is mostly from peripheral arthritis, setting it apart from AS, which always and mostly involves the spine.
If you or a loved one has symptoms of either PsA or AS, it’s best to speak with a health care provider or rheumatologist to help pin down a diagnosis. While distinguishing between PsA and AS and ruling out other related conditions can take time, it’s critical to have an accurate diagnosis to start managing the condition as soon as possible and improving your quality of life.
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