Psoriatic arthritis (PsA) and ankylosing spondylitis (AS) are both types of arthritis and chronic (ongoing) diseases of the 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 the 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. This leads 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 the expertise of a healthcare provider, it can help to know the key differences between the two conditions. Distinguishing between PsA and AS is critical to getting the right treatment plan and preventing potential long-term issues such as further joint damage.

What Is Psoriatic Arthritis?

PsA is a type of arthritis that is linked to psoriasis, a skin and nail condition. Around 3 in 10 people with psoriasis develop PsA. Some people may have PsA without ever having (or noticing) psoriasis symptoms, 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 ankylosing spondylitis.

Common Psoriatic Arthritis Symptoms

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:

• Red, discolored joints that may be warm to the touch
• Stiff, painful, swollen, and tender joints
• Inflammation causing swollen fingers and toes, resulting in a sausagelike appearance
• Morning tiredness and stiffness
• Decreased range of motion
• Changes in the nails, such as separation from the nail bed or pitting
• Uveitis (redness and pain in the eyes)

What Is Ankylosing Spondylitis?

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 (or spondyloarthritis) is an umbrella term for several types of arthritis that usually affect the spine. Other types of spondylitis include enteropathic arthritis, PsA, reactive arthritis, undifferentiated 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.

Common Ankylosing Spondylitis Symptoms

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:

• Stiffness of the spine, especially in the morning
• Stooped posture due to bending over to relieve back pain
• Difficulty taking a deep breath due to affected rib and spine joints
• Joint pain
• Loss of appetite and weight loss
• Anemia
• Fever
• Fatigue
• Skin rashes
• Eye inflammation
• Organ damage
• Digestive problems (such as inflammatory bowel disease, including ulcerative colitis and Crohn’s disease)

What’s the Difference Between Ankylosing Spondylitis and Psoriatic Arthritis?

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 in PSA and ankylosing spondylitis include whether there’s back pain and skin and nail problems, and which joints are affected.

Back Pain

One of the main distinguishing symptoms between AS and PsA is back pain. AS always involves the spine, causing back pain, whereas PsA more often causes pain in the peripheral joints.

For example, a member of MyPsoriasisTeam 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.”

Skin and Nail Issues

Another key difference in symptoms between PsA and AS is the presence of skin and nail issues. Psoriasis and nail issues are common in people with PsA, but rare for people with AS. Only about 10 percent of people with AS also have psoriasis.

Joint Pain Location

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. A 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.

Causes of Psoriatic Arthritis and Ankylosing Spondylitis

The exact cause of PsA is unknown, but genes, immunity, and the environment may play a role. Having a family member with PsA increases the risk of developing the condition. Some people may develop PsA after an injury.

Similarly, the causes of AS aren’t clear, but genetics seem to play a part. One gene, called HLA-B27, has been studied for its connection to AS. Still, having this gene doesn’t mean you’ll definitely get the disease.

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. AS may affect more young men than women, according to Johns Hopkins Medicine.

Diagnosing Psoriatic Arthritis vs. Ankylosing Spondylitis

As both PsA and AS are arthritic conditions, diagnosis is best made by a rheumatologist or a healthcare professional with expertise in conditions that affect the joints, bones, and muscles. 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 healthcare 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 healthcare provider will likely ask about your patterns of joint pain. They may also look for skin and nail issues, which are common in PsA but not AS, or take a skin biopsy.

If a healthcare 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.

Treating Psoriatic Arthritis vs. Ankylosing Spondylitis

Treatment options for PsA and AS depend on factors like your symptoms and the severity of the disease. Although there’s no cure for PsA or AS, certain medications can help treat the symptoms and slow the progression of each condition. Some treatments overlap, but some medications are better for one condition versus the other.

Treating Psoriatic Arthritis

Early PsA treatment is the best way to help protect joints from damage. Some medications that may be used to treat PsA include:

• Nonsteroidal anti-inflammatory drugs (NSAIDs) to manage symptoms
• Immunosuppressive medications, corticosteroids (steroids), or biologics (medications made from living cells) to reduce inflammation
• Calcium and vitamin D to strengthen the bones

Other treatments may include lifestyle changes or nonmedical therapies. A healthcare provider might recommend the following nonmedical treatments to help manage PsA symptoms:

• Occupational or physical therapy
• Exercise
• Heat and cold packs
• Splints
• Ultraviolet light treatment

If PsA symptoms are severe, surgery may be recommended to replace or repair a damaged joint.

A member of MyPsoriasisTeam commented about their experience with PsA surgery, saying, “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.”

Treating Ankylosing Spondylitis

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, such as for joint replacement or removal of thickened or hardened bone. Rods may also be placed in the spine.

Other AS treatments may include:

• Interleukin-17A and JAK inhibitors to reduce inflammation and swelling
• Muscle relaxants and pain inhibitors to reduce severe pain
• Disease-modifying antirheumatic drugs to reduce inflammation

Always make sure to ask your healthcare or rheumatology provider how long you should take certain medications, as some may only be recommended for a short period of time.

Can You Have Both Ankylosing Spondylitis and Psoriatic Arthritis at the Same Time?

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 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 healthcare 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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