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Psoriatic Arthritis Differential Diagnosis: Diseases That Mimic PsA

Psoriatic arthritis (PsA) is often confused with other inflammatory conditions with similar symptoms. Learn how differential diagnosis for PsA works. Psoriatic arthritis (PsA) is a type of psoriatic disease that primarily affects the joints and entheses (areas where bones meet ligaments and tendons) throughout the body. It is sometimes linked to a second kind of psoriatic disease called

  • Posted on 22nd May, 2022 00:30 AM
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Psoriatic Arthritis Differential Diagnosis: Diseases That Mimic PsA Image

Psoriatic arthritis (PsA) is a type of psoriatic disease that primarily affects the joints and entheses (areas where bones meet ligaments and tendons) throughout the body. It is sometimes linked to a second kind of psoriatic disease called psoriasis, which primarily affects the skin.

With both types of psoriatic disease, the immune system will malfunction for unknown reasons and start to attack healthy tissues. Some people will have both PsA and psoriasis, while others with PsA may never get psoriasis.

What causes PsA is unknown, but researchers believe there is a genetic component to PsA. In addition, certain external factors might contribute, including infection, physical trauma, smoking, and chronic stress.  

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No cure exists for PsA, but it is a treatable and manageable condition. Treatment can help to control inflammation and prevent joint damage and disability.

Statistics

According to a 2015 Rheumatic Disease Clinics of North America report, PsA prevalence ranges from around 0.06% to 0.25% in the United States. White people are more frequently affected compared to Black people and Native Americans.

PsA affects all sexes equally and generally develops between the ages of 30 and 50. PsA can also affect children, with an average age of onset in this group of 13 years of age.

This article will cover PsA symptoms, differential diagnosis, diagnostic tools, misdiagnosis, and more.

Psoriatic Arthritis Symptoms  

About 30% of people with psoriasis will develop PsA, according to the National Psoriasis Foundation. That means they will have experienced skin symptoms before having joint pain.

It is possible to experience joint symptoms first. And some people will never have psoriasis or skin symptoms related to PsA.

Psoriasis Skin Symptoms

The most common skin symptoms in psoriasis are dry, raised skin lesions called plaques. These plaques are covered with silvery-white scales. Plaques can be itchy, painful, and inflamed. They can also bleed and crack.

PsA joint symptoms can affect any joint in the body, causing pain, stiffness, swelling, and reduced range of motion. PsA can be asymmetrical (affecting joints on one side of the body) or symmetrical (involving the same joints on both sides, such as both hands or both knees).

For some people, the condition will start gradually and slowly worsen. For others, it might come on suddenly and become painful and severe very quickly.

In addition to joint symptoms, PsA can cause the following:

  • Dactylitis: This condition causing painful swelling of the fingers and toes is sometimes called "sausage digits," because the fingers get so swollen, they look like small sausages.
  • Enthesitis: Inflammation and pain can develop in the entheses, especially at the heels and soles of the feet.
  • Back, hip, and shoulder pain: PsA can lead to a condition called psoriatic spondylitis, which affects the spine and nearby joints.
  • Skin symptoms: These include thick, red patches called plaques.
  • Nail symptoms: Symptoms include pitting, ridging, discoloration, nail bed separation, and skin cell buildup under the nails.
  • Costochondritis: Inflammation in the area linking the breastbone and ribs leads to chest and rib pain.
  • Uveitis: This eye inflammation causes blurry vision, floating spots in the line of sight, eye pain, eye redness, and sensitivity to light.
  • Fatigue: Extreme tiredness and exhaustion adversely affect daily function.
  • Arthritis mutilans: Some people will develop a rare but severe, destructive form of PsA that attacks the joints of the fingers and toes. This subtype of PsA affects about 5% of the people with the condition.

Psoriatic Arthritis Differential Diagnosis

No single test can confirm a diagnosis of PsA, and other diseases can cause similar symptoms, especially other types of inflammatory arthritis.

With a differential diagnosis, your healthcare provider will look at the possible conditions that could cause the symptoms you are experiencing. This process involves different testing methods to rule out certain diseases or to determine if further testing is needed. 

Conditions that cause similar symptoms to PsA and are included in a differential diagnosis are:

Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a type of inflammatory arthritis that attacks the synovium—the lining of the joints. RA is a symmetrical disease that affects the same joints on both sides of the body, such as both wrists or knees. Like PsA, RA might affect internal organs.

Left untreated, RA and PsA can lead to joint damage, mobility and function troubles, and disability. Both conditions can cause similar complications, such as life-threatening infections, heart disease, and lung problems.

PsA and RA are both autoimmune diseases, which means they occur because the immune system has malfunctioned and has started attacking healthy tissues. They are treated similarly, with disease-modifying antirheumatic drugs (DMARDs) and biologics.

PsA vs. RA

PsA and RA can be easy to mix up because they both cause pain, stiffness, and swelling of joints. But PsA inflammation frequently shows up on the spine and in the entheses, whereas RA inflammation is more common in the synovium. Also, RA rarely causes a skin rash or nail symptoms.

Gout and Pseudogout  

Gout and pseudogout are types of arthritis caused by the accumulation of crystals in the joints. Gout is caused by uric acid crystals and pseudogout by calcium pyrophosphate crystals.

Symptoms of gout and pseudogout include intermittent episodes of red, hot, and swollen joints. These attacks often start in the middle of the night. Both gout and pseudogout are common in the big toe but can affect other joints, including the knees, wrists, ankles, and elbows.

People with PsA can suddenly develop joint symptoms, just like people with gout or pseudogout. And people with PsA can have one swollen toe or one swollen finger.

People with PsA have a higher risk of developing gout. While researchers do not know exactly why this occurs, they suspect that high uric acid levels might be the result of high skin cell turnover and inflammation related to psoriasis and PsA.

PsA vs. Gout/Pseudogout

A key difference between PsA and the conditions of gout and pseudogout is that gout and pseudogout affect one or two joints during an attack, while PsA will affect multiple joints and cause nail and skin symptoms.

Also, joint swelling in gout and pseudogout can go away in a week or two, sometimes without any treatment, and PsA needs persistent treatment. Gout and pseudogout cause joints to be much more swollen and tender, and those joints feel hot to touch rather than warm as with PsA.

Osteoarthritis

Osteoarthritis (OA) is a degenerative condition in which the tissues of the joints break down over time. OA causes some joint symptoms similar to those seen in PsA.

For example, like PsA, people with OA can experience joint pain after activity and stiffness after rest and inactivity. The joints most commonly affected by OA are the knees, hips, hands, neck, and low back.

PsA vs. OA

OA and PsA have more differences than they do similarities. For example, OA is caused by mechanical wear and tear on joint cartilage and bones, and PsA is an autoimmune disease that attacks the joints and other body tissues.

Also, people with PsA have a lot of stiffness that is worse in the morning and improves throughout the day as they use their joints, but stiff joints in OA resolve within 30 minutes. People with PsA experience pain from ongoing inflammation and joint pain without exerting themselves, whereas OA pain worsens with use.

Reactive Arthritis

PsA and reactive arthritis are types of spondyloarthritis, arthritis conditions that affect the spine.

Reactive arthritis is triggered by a bacterial infection, such as Chlamydia, Salmonella, or Campylobacter, bacteria transmitted through contaminated food or sex. These bacteria are quite common, and most people who have been exposed to them will not develop reactive arthritis. But for a small genetically predisposed group of people, their immune systems will overreact and cause joint pain and other symptoms.

Like PsA, reactive arthritis can cause asymmetric pain in the lower back and lower limbs. It can also cause enthesitis and dactylitis. Reactive arthritis might also cause eye inflammation.

Symptoms of reactive arthritis often go away with treatment within three to 12 months. For about 30%–50% of people, symptoms will return later or become a long-term problem.

PsA vs. Reactive Arthritis

A primary difference between PsA and reactive arthritis is that a bacterial infection causes reactive arthritis. Reactive arthritis also causes urinary tract inflammation, which is rarely seen in PsA.

A unique feature of reactive arthritis is that it may not return after the first occurrence or it can return with long-term mild arthritis. This isn't the case for PsA, which is lifelong and will progressively become worse.

Septic Arthritis

Septic arthritis is an infection of the synovial (joint) fluid and joint tissues. It is common in children, but it can also affect adults. Different types of bacteria, viruses, and fungi can affect the joint when they enter the bloodstream.  

Septic arthritis causes similar symptoms to PsA, including joint pain and swelling. Much like PsA, untreated septic arthritis can lead to permanent joint damage.

PsA vs. Septic Arthritis

Symptoms of septic arthritis are localized to the affected areas, whereas PsA joint symptoms can affect multiple joints in different body areas. Septic arthritis generally presents with fever, and PsA usually does not.

Lastly, septic arthritis is treatable with antibiotics, and symptoms often do not return. But PsA is a chronic condition that requires lifelong treatment.

Axial Spondyloarthritis  

The term axial spondyloarthritis (axSpA) is an umbrella term for types of inflammatory arthritis that mainly affect the spine and sacroiliac (SI) joints (the joints connecting the lower spine to the pelvis). The result is pain in the low back, buttocks, and hips.

The two types of axSpA are non-radiographic axial spondyloarthritis (nr-axSpA) and ankylosing spondylitis (AS). They cause symptoms similar to PsA, and many people with nr-axSpA and AS will have pain in the peripheral joints (limb joints). AxSpA conditions might also cause dactylitis and enthesitis.

PsA vs. axSpA

PsA and axSpA differences are subtle, but those differences help your healthcare provider tell them apart. For example, AS primarily affects the spine. While spine involvement can occur in PsA, PsA mainly affects the peripheral joints, shoulders, and hips.

PsA also frequently affects the fingers and toes and causes skin and nail symptoms—symptoms rarely seen in axSpA.

Plantar Fasciitis  

Plantar fasciitis refers to inflammation of the band of tissue at the bottom of your foot (the plantar fascia), causing heel pain. Heel pain can also occur in PsA.

With plantar fasciitis, the cause is repetitive stress on the tissue from physical activity, weight, or standing on the feet all day. But in PsA, plantar fasciitis occurs because of enthesitis in areas where ligaments attach to bone.

PsA vs. Plantar Fasciitis

Plantar fasciitis, on its own, is limited to the plantar fascia. But PsA causes enthesitis at the plantar fascia because of your immune system’s overactive response.

If plantar fasciitis doesn’t improve with treatment and time or keeps recurring, consider asking your healthcare provider for further testing to determine if PsA or another condition might be causing your symptoms.

How to Diagnose Psoriatic Arthritis

An early and accurate diagnosis is vital to avoid the damage and deformity PsA is known for causing. Your healthcare provider will employ different diagnostic tools to determine the cause of symptoms.

Diagnostic methods for PsA generally include:  

  • Medical and family history, including symptoms
  • A physical exam
  • Lab work
  • Imaging 

Medical and Family History 

Your healthcare provider will ask about any personal history with psoriasis or family history of psoriatic disease. While there is no known inheritance pattern for PsA, 40% of people with PsA will have a family history of PsA or psoriasis.

Of course, having a family history does not mean you will develop either condition. And getting PsA without any personal or family history is also possible because gene mutations can sometimes be sporadic.

After learning about your personal or family history of psoriatic disease, your healthcare provider will want to know what symptoms you are experiencing or have previously had. You can help your healthcare provider by keeping track of symptoms for a few weeks before your visit.

Your healthcare provider will want to know:  

  • Symptoms experienced: These may include joint pain, digit swelling, back pain, and skin or nail symptoms.
  • A description of symptoms: Joint pain can include burning, stabbing, and aching.
  • Symptom severity: You will be asked for severity based on a scale of 1 to 10, with 10 being the most severe.
  • Symptom frequency: Do symptoms come and go, or have they remained persistent?
  • Symptom triggers: Do certain factors bring about symptoms or worsen them, such as stress, smoking, exercising, and certain foods?
  • What helps symptoms, if anything: An example is an anti-inflammatory pain reliever for joint pain.

Physical Examination 

A physical examination for PsA involves examining joints, skin, nails, and entheses. When examining the joints, your healthcare provider will touch for tenderness and swelling of the fingers and toes, feet, hips, and knees.

With the entheses, they will look for soreness and tenderness at the heels and soles of the feet, ribcage, and pelvis. The skin and nails are examined for skin plaques, lesions, and nail symptoms.  

Lab Work

There is no single blood test that confirms PsA. But your healthcare provider will request blood work to rule out other types of inflammatory arthritis and determine how much inflammation you might be experiencing. Tests include:

Imaging  

If your healthcare provider suspects PsA or cannot determine a diagnosis from other testing methods, they will request imaging studies, including X-rays, magnetic resonance imaging (MRI), or ultrasound scans. Imaging in PsA can be beneficial.  

According to a 2018 report in the journal Arthritis & Therapy, PsA can cause bone erosion (loss of normal bone) and joint destruction early in the disease process. These kinds of bone and joint changes are specific to PsA and rarely seen with other types of inflammatory arthritis.  

Different types of imaging can identify patterns of what is going on with your joints. For example, X-rays might be able to identify bone erosion, bone spurs, and joint space changes—a sign of cartilage or soft tissue damage.

An MRI can offer more detailed imaging, including visualization of the entheses and hip joints. Ultrasound can pinpoint inflammation and is sensitive enough to detect joint damage early. 

Reasons for Misdiagnosis and How to Avoid It

According to a 2021 Mayo Clinic study, more than half of the people with PsA wait an average of over two years for a correct diagnosis after initial symptoms. Researchers found the time from the first PsA symptoms to diagnosis among patients ranged from six months to almost seven years.  

There were many reasons why PsA might be misdiagnosed, according to the researchers. These included:  

  • The younger people were at the start of symptoms, the more they were likely to dismiss symptoms and less likely to report them to their healthcare provider.
  • Because enthesitis was not a common symptom, healthcare providers dismissed it as pain or swelling from overuse or trauma.
  • People who were overweight had other conditions that could explain their joint pain, including OA and gout, and PsA was not considered.

Another reason for misdiagnosis might be a shortage of rheumatologists—doctors specializing in rheumatic (inflammatory) diseases like PsA. According to a 2015 Workforce Study of Rheumatology Specialists, there are 14% fewer full-time rheumatologists than what would be considered ideal, and that number is expected to decrease further in the coming years.

Avoiding a Misdiagnosis

Misdiagnoses lead to consequences, such as being prescribed the wrong medicines to delays in treatment, which can lead to severe problems in PsA, including bone and joint damage. But there are measures you can take to help your doctor reach an accurate diagnosis and avoid delays in treatment, including:

  • See a rheumatologist: If you have a personal history of psoriasis, a family history of psoriatic disease, or if your healthcare providers suggest you might have inflammatory arthritis, ask for a referral to a rheumatologist.
  • Track symptoms: When you meet with your healthcare provider or new rheumatologist, that time is limited to a 10- to 20-minute window, so preparing ahead can be helpful for you and your provider. Keep a journal to track symptoms and any treatment you are on. Take your notes with you and have them available to share with your healthcare provider.
  • Ask questions: It can be easy to accept a diagnosis and take treatments simply because your healthcare provider has said so. However, asking questions and being actively involved is much more helpful, especially if a diagnosis ends up being wrong. Ask questions like, "Is this the only possible diagnosis?" Or, have you considered something else? Asking these questions opens up opportunities for further evaluation and a more accurate diagnosis.
  • Be proactive: Your electronic medical record can give you access to test results as soon as they are available. You can also view medical appointments, treatment plans, and after-visit notes your healthcare provider has made. Take the time to review this record and make sure everything is accurate.

Your healthcare provider is extremely busy, so it is possible to miss something. As a proactive patient, you get to take control and keep on top of what is happening, and that includes being a part of an accurate diagnosis.

When to See a Healthcare Provider

PsA is a progressive disease that will worsen with time. And if it is not adequately treated, it could lead to life-threatening complications. It is vital to get a timely diagnosis and start treatment early to avoid joint and bone damage.  

If you have a personal medical history of psoriasis or a family history of psoriatic disease, reach out to your healthcare provider as soon as you start to experience signs of PsA.  And even without personal or family history, it is still important to reach out early.  

Reach out to your healthcare provider if you experience one or more of the following symptoms:

  • Joint pain, swelling, and stiffness that lasts for days and recurs
  • Morning stiffness or stiffness after periods of activity that lasts a half hour or more
  • Finger or toe swelling with no known cause that lasts for two or more weeks, doesn’t resolve with home treatment, or returns weeks or months later
  • Nail symptoms common in PsA
  • Skin symptoms seen in psoriasis if you have never been diagnosed with psoriasis
  • Chronic fatigue that lasts two or more weeks and affects your ability to function in daily life

Summary

Psoriatic arthritis is an autoimmune disease in which the immune system malfunctions and attacks the joints, entheses, and skin. PsA shares symptoms with other types of arthritis, so diagnosing it requires a differential diagnosis approach. That means your healthcare provider will look at other possible conditions, along with PsA, that might be causing your symptoms.

A thorough diagnosis will involve a physical examination, blood work, imaging, and more. Misdiagnoses are common PsA. It is good to be proactive so that PsA is not missed and treatment is not delayed.

A Word From Verywell

Diagnostic delays in psoriatic arthritis can lead to irreversible joint damage. That means it is crucial to identify the condition early as possible and start treatment immediately. It is also vital to take your PsA medication consistently and as directed by your healthcare provider. This is the best way to prevent the disease from progressing. 

If you are unsure of how to take medications or cannot take them either due to cost or side effects, talk to your healthcare provider. There are many options available for treating PsA, and there is a unique treatment plan that fits your symptoms, disease, and lifestyle. Be sure to discuss all your options with your healthcare provider and your ability to stick with that plan.

Frequently Asked Questions

  • How does psoriatic arthritis differ from other types of arthritis?

    Psoriatic arthritis has some unique qualities that set it apart from other types of arthritis. It tends to be asymmetric, although people with advanced disease might experience a symmetric disease pattern. PsA also causes skin plaques, similar to psoriasis, and nail symptoms like pitting, ridging, discoloration, and nail bed separation.

  • How is psoriatic arthritis diagnosed?

    No single test can confirm a psoriatic arthritis diagnosis. However, your healthcare provider will use different diagnostic tools, including a physical examination, medical and family history, blood work, other lab work, and imaging, to assist in making a diagnosis and ruling out other conditions that cause similar symptoms.

  • How can I ensure my diagnosis is correct?

    If your primary care or family medicine healthcare provider suspects you have arthritis, they will refer you to a rheumatologist, who can diagnose you and set up a treatment plan.

    You can help your healthcare provider ensure a correct diagnosis by providing as much information as possible about the symptoms you experience, their severity and location, when symptoms started, what triggers them, and what alleviates them.

    You should also share any personal or family histories of psoriatic disease with your healthcare provider.

  • Is psoriatic arthritis curable?

    No. There is no cure for psoriatic arthritis, but it is possible to experience disease remission. That means you still have PsA, but you have no symptoms or very little disease activity. It is possible to achieve remission with the help of medication, including DMARDs and biologics.

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