Psoriatic Arthritis vs. Ankylosing Spondylitis: What Are the Differences?

Both psoriatic arthritis (PSA) and ankylosing spondylitis (AS) are types of spondyloarthritis, inflammatory diseases that affect the hands, feet, back, pelvis, neck, and larger joints. Spondyloarthritic conditions can also affect the skin, eyes, and other organs. The most common form of spondyloarthritis is AS.

Both PsA and AS cause joint pain, swelling, and stiffness. PsA primarily affects the hands and feet, and large joints, including the knees and ankles. In AS, symptoms mainly affect the back and sacroiliac joints, the area where the spine connects to the pelvis, although other joints can be affected.

If left untreated, both PsA and AS can cause permanent damage to joints. An early and correct diagnosis is vital for both these conditions so your doctor can start you on a treatment plan to ease pain and prevent long-term problems.

PsA and AS are often confused with other types of inflammatory arthritis, and sometimes they are mistaken for each other. This article will discuss the similarities and differences of PsA and AS, including symptoms, causes, and treatments.

Symptoms

PsA and AS can share similar symptoms and features. Spondyloarthritic conditions are considered axial, which means they mainly affect the spine. They can also be peripheral, meaning they mainly affect other joints, including the hands, feet, and knees.

PsA is often considered peripheral and AS is considered axial, but axial and peripheral features can overlap in different types of spondyloarthritis.

Psoriatic Arthritis

PsA affects 60 to 250 per 100,000 American adults. It affects one in three people with the autoimmune skin condition psoriasis. Psoriasis causes skin cells to grow quickly, leading skin cells to pile up in scaly, silvery patches, called skin plaques.

PsA can affect various joints, including the arms, legs, spine, hands, and feet. It is categorized into five major types.

The five types are:

• Distal interphalangeal predominant (DIP), which primarily affects the small joints of the tips of the fingers and toes
• Symmetrical polyarthritis, which affects multiple small joints of the hands and feet
• Asymmetrical oligoarthritis and monoarthritis, which affects only a few joints (oligo) or one joint (mono) of the fingers and toes
• Psoriatic spondylitis (axial disease), which mainly affects the bones of the spine
• Arthritis mutilans, an extremely severe and destructive form of PsA known for causing deformity of the hands, feet, and spine and is the leading cause of disability among people with PsA
  

The symptoms of PsA may come on gradually and mildly for some people. For others, they may be sudden and severe. Not all people with PsA will experience the same symptoms.

The most common symptoms of PsA are:

• Pain, tenderness, and/or swelling of one or more joints: Usually the hands, feet, wrists, knees, and ankles
• Joint stiffness: Most noticeable upon waking in the morning and after sitting for a long time
• Reduced range of motion in affected joints
• Pain and stiffness in the lower back
• Enthesitis: Pain, tenderness, and swelling of the entheses, the areas where tendons and ligaments attach to bone
• Dactylitis: Swelling of the entire fingers and toes, causing them to look like sausages
• Skin symptoms: Silver, scaly patches that appear on the scalp, elbows, knees, and lower part of the spine, and/or small, red spots called papules on the arms, legs, and torso
• Nail symptoms: Pitting (small depressions) of the nails, and nail bed separation
• Eye inflammation: Iritis (inflammation of the iris, the colored part of the eye) or uveitis (inflammation of the uvea, the middle layer of tissue in the eyeball)
• Chronic fatigue: Fatigue that results from inflammatory processes that cause the immune system to work overtime (Researchers note that 30% of people with PsA experience significant fatigue, which correlates to the degree of psoriasis a person with PsA experiences.)
• Anemia: Low red blood cell counts

Ankylosing Spondylitis

According to the Johns Hopkins Arthritis Center, the prevalence of AS in the United States is around 200 to 500 of every 100,000 people. The earliest signs and symptoms of AS might include pain and stiffness in the lower back and hips, especially in the morning and after being inactive for a long period.

Additional symptoms of AS include:

• Neck pain: AS causes inflammation of the cervical spine (neck region).
• Joint pain: The joints most commonly affected by AS are the base of the spine and pelvis, the vertebrae in the low back, and the hip and shoulder joints.
• Breathing difficulties: AS affects the cartilage between the breastbone and ribs, which causes chest wall pain and, sometimes, breathing troubles. Severe or untreated AS can lead to a wide range of cardiopulmonary manifestations, including “aortitis, aortic valve diseases, conduction disturbances, cardiomyopathy, and ischemic heart disease.”
• Gastrointestinal pain: This includes abdominal pain and diarrhea.
• Skin rash: Spondyloarthiritis frequently presents with skin symptoms, including those seen in PsA and psoriasis.
• Vision problems: AS causes similar eye inflammation troubles to PsA.
• Enthesitis: Researchers believe enthesitis is one of the first symptoms that occur with AS. The more inflammation of the entheses, the more bone wears away.
• Joint fusion and calcification: As the body builds more bone tissue, too much will be formed, causing joint fusion and spinal ligament calcification. These fusions are called syndesmophytes.
• Chronic fatigue: AS can make you feel as if your energy is zapped. Levels of fatigue can be extremely high.
• Buttock and hip pain
• Shoulder pain

What Makes PsA Different From AS?

While PsA and AS have many similar symptoms, there are specific symptoms that set them apart.

Symptoms that set these conditions apart include:

• Back pain: PsA sometimes affects the spine and leads to back pain, but AS always affects the spine.
• Joint inflammation locations: PsA frequently affects the finger and toe joints. It also causes peripheral joint problems (arms and legs). It's less common for AS to affect the peripheral joints.
• Skin and nail problems: PsA is more commonly linked to skin and nail problems from psoriasis. While it is possible to have psoriasis and/or skin and nail problems with AS, it is less common. The majority of people with PsA experience skin and nail symptoms.

Both PsA and AS come with long waiting periods for diagnosis, up to 10 years in some cases. This is because they can be mistaken for other conditions, including fibromyalgia, rheumatoid arthritis, and osteoarthritis. They can also be mistaken for each other.

Causes

PsA and AS are both autoimmune diseases, conditions in which the immune system malfunctions and attacks healthy tissues. Much like other autoimmune diseases, PsA and AS have no specific known causes, although genetics is believed to be involved. 

In particular, many people with spondyloarthritis conditions have a gene called HLA-B27, which puts them at higher risk for their conditions. However, not everyone with this gene will develop PsA, AS, or another spondyloarthritis condition.

One 2021 report in the journal Frontiers in Immunology reports that 75%–90% of people with AS test positive for HLA-B27, and 20%–50% of people with PsA have this gene marker.

Psoriatic Arthritis

Researchers think PsA develops from a combination of genetic and environmental factors. They suspect immune system problems, infections, obesity, smoking, chronic stress, and physical trauma all play a part in determining who might develop the condition.

The people who have the highest risk for PsA are those with psoriasis, but it is very possible to have PsA without psoriasis or to have psoriasis and not develop PsA.

Having a family history of PsA or psoriasis increases your risk for PsA. A child whose parent has PsA or psoriasis has a greater risk for PsA.

According to the Cleveland Clinic, research on PsA has found increased levels of tumor necrosis factor (TNF) in the joints and affected skin of people with PsA. These higher levels are responsible for overwhelming the immune system and causing it to produce the inflammation responsible for PsA.

Known risk factors for PsA include:

• Chronic stress
• Skin injury
• The use of certain medicines
• Viral and bacterial infections
• Tobacco
• Overconsumption of alcohol
• Psoriasis: Skin or nail
• Obesity

PsA affects males and females in equal numbers. It most frequently occurs in adults ages 35 to 55, but it can affect anyone regardless of age, including children.

Ankylosing Spondylitis

Much like PsA, AS can run in families, and the HLA-B27 gene can be inherited. Having the HLA-B27 gene increases your risk for AS to about 50%.

Still, having this gene isn't enough to cause the disease to develop. Other factors—environmental (including infection, trauma, and chronic stress, etc.) and even sporadic events—in association with the gene contribute to disease development.

AS has a strong genetic component, as shown in family and twin studies. The sibling risk for AS is 9.2% compared to 0.1% in the general population. The most direct evidence on family history is the rates of AS in HLA-B27-positive identical twins­ at around 60% risk and 27% for HLA-B27-positive fraternal twins.

Risk factors for AS are:

• Being male: Males are more likely to have AS than are females.
• Age: The most frequent age of onset is late adolescence or early adulthood.
• Family history: AS has a genetic link.
• Coexisting conditions: Having other autoimmune diseases, such as psoriasis, Crohn's disease, or ulcerative colitis can increase risk.

Diagnosis

The correct diagnosis for PsA or AS is essential. It is best done by a rheumatologist, a doctor who has additional training and experience in diagnosing and treating diseases of the joints, bones, and muscles. There is no single test that can confirm either condition, so doctors will focus on ruling out other conditions.

One of the first steps in looking for a diagnosis starts with your doctor asking about family and medical history and symptoms. A physical exam will also look for joint pain patterns and pain areas, nail and skin symptoms, and eye inflammation.

Lab work, including blood work and joint fluid samples, can help in diagnosing PsA or AS. Blood work looks for inflammation and helps to rule out other types of inflammatory conditions like rheumatoid arthritis. Testing joint fluid can help rule out gout, which causes uric acid crystal buildup in the joint fluid.

If your doctor suspects PsA or AS, they will request X-rays to check for joint damage. Magnetic resonance imaging (MRI) and ultrasound can find inflammation and bone changes. Sometimes, skin biopsies are done to determine if psoriasis is involved.

If your doctor suspects AS, you will likely be tested for HLA-B27. Because HLA-B27 is seen less frequently in people with PsA, the test is done to predict whether PsA might affect your spine.

Treatment

No cure exists for either PsA or AS, but both conditions are treatable and manageable. Treatment is aimed at managing symptoms, protecting the joints, slowing down disease progression, and improving quality of life. Your rheumatologist will work with you to determine the best plan of action that meets your health needs. 

Treatments for PsA and AS tend to overlap, but certain medications might be better for treating one condition over the other.

Psoriatic Arthritis

Nonsteroidal anti-inflammatory drugs (NSAIDs) like Advil (ibuprofen) and Motrin (naproxen) are used for mild cases of PsA.

If a person experiences a more moderate disease, their doctor will also prescribe disease-modifying antirheumatic drugs (DMARDs) or biologics. These suppress their overactive immune system and reduce inflammation to help manage pain and other symptoms. 

DMARDs commonly prescribed to treatment PsA include Trexall (methotrexate), Arava (leflunomide), and Azulfidine (sulfasalazine). Common biologic drug therapies used in treating PsA are TNF inhibitors, interleukin (IL) inhibitors, and T-cell inhibitors.

Newer treatments for PsA are Janus kinase (JAK) inhibitors, including Rinvoq (upadacitinib) and Xeljanz (tofacitinib). These medicines work to tamp down the immune system and prevent inflammation that leads to joint damage. In addition, Otzela (apremilast), another newer treatment for PsA, helps control inflammation by blocking an enzyme called phosphodiesterase type 4 (PDE4). 

People with PsA who have skin symptoms also benefit from topical treatments, including corticosteroid creams and anti-inflammatory medications, as well as phototherapy (treatment by exposure to ultraviolet, or UV, light) to reduce and manage the effects of itching and skin pain.

Surgery for managing PsA is rare, but it can be used if joints are severely damaged to improve mobility and relieve discomfort.

Ankylosing Spondylitis

NSAIDs are considered first-line therapy for treating AS. But if these medicines don’t help manage inflammation and other AS symptoms, your doctor will prescribe biologic drug therapies.

Different types of biologics are used to treat AS, including TNF inhibitors and IL-17 inhibitors. Cosentyx (secukinumab) and Taltz (ixekizumab) are the two most prescribed biologics for AS, but many others have been used to help manage symptoms in people with AS.

In April 2022, The Food And Drug Administration (FDA) approved Rinvoq, a once-daily pill to treat adults with active AS who have had an inadequate response or intolerance to TNF inhibitors. Other JAK inhibitors approved to treat AS include Xeljanz. JAK inhibitors may increase your risk of severe side effects, including infections, heart-related events, cancer, blood clots, and death.

Much like PsA, surgery for AS is only done in the most severe cases. When it is done, it is usually done to straighten the spine.

Lifestyle Changes

People who live with PsA or AS can benefit from making healthy lifestyle choices.  

Lifestyle changes might include:

• Being active: Being physically active helps build the strength of joints and muscles, prevents stiffness, and maintains flexibility and mobility. Exercises generally safe for people with PsA and AS are swimming, walking, yoga, and biking. Check with your healthcare professional on which exercises are the safest for you.
• Eating healthy: For both PsA and AS, it is important to eat a balanced diet and keep a healthy weight to reduce pressure on your joints and keep inflammation down. It helps relieve symptoms, keeps medications working effectively, and reduces your risk for complications and other serious health conditions.
• Quitting smoking and reducing alcohol intake can reduce PsA and AS symptoms and keep your medications working effectively.
• Nondrug options like hot and cold therapy, braces or splints, and stress management techniques, such as deep breathing may be helpful.

Prevention

Autoimmune diseases and spondyloarthritis generally cannot be prevented. If you have a family history of PsA, AS, autoimmune diseases, or spondyloarthritis conditions, ask your doctor to help you identify risk factors for developing these conditions.

While researchers know that people with psoriasis might have a higher risk for PsA and some people have genetic markers that increase their risk for PsA and AS, no specific treatment can prevent these conditions. There is no way to identify people who may go on to develop these conditions. 

Some risk factors and triggers for PsA and AS can be prevented—such as smoking, diet, and exposure to chronic stress. But even with managing these, you can still end up with PsA, AS, and other similar diseases.

If you are concerned about your risk for PsA or AS, reach out to your healthcare provider to discuss this risk and be evaluated for these conditions. Early diagnosis can help reduce the risk for joint damage.

Summary

PsA and AS are two common types of spondyloarthritis, inflammatory conditions that affect the back, pelvis, neck, and larger joints. These conditions share many characteristics, including symptoms and genetic causes.

They can also be challenging to diagnose, and neither disease can be cured. Fortunately, there are many treatment options to ease pain and other symptoms and improve your quality of life. Prevention of PsA and AS is not always possible, although managing some risk factors can reduce your risk.

A Word From Verywell

Both PsA and AS can worsen as you age but they are not disabling or life-threatening for most people. However, symptoms, such as joint pain, back pain, and fatigue can interfere with your quality of life.

Talk to your healthcare provider about how you can manage symptoms of PsA or AS so that you can continue to be active and enjoy life.