How Psoriatic Arthritis Is Diagnosed

Diagnosis involves a process of elimination

In This Article

When diagnosing psoriatic arthritis, the focus is placed on distinguishing it from other types of arthritis, such as gout, rheumatoid arthritis, or osteoarthritis. The diagnosis involves a physical examination, a review of your medical history, and X-rays or other imaging studies. Blood tests and synovial fluid analyses may be also be performed to rule out other types of arthritis.  

Psoriatic arthritis is a type of inflammatory arthritis that belongs to a group of conditions known as spondyloarthropathies. It is a progressive autoimmune disease that affects both the joints and skin and, if not properly diagnosed and treated, may lead to permanent joint damage and disability. 

Psoriatic arthritis responds well to certain medications and less so to those used for other types of arthritis. This is why getting an accurate diagnosis is so important.

At-Home Screening

Psoriatic arthritis has two main components: psoriasis and arthritis. Psoriasis is characterized by an autoimmune assault on cells of the outer layer of skin (called the epidermis). The resulting inflammation can, over the long term, affect the joints as well as the skin, leading to psoriatic arthritis.

While psoriatic arthritis can occur on its own, around 85% of cases are preceded by psoriasis, says a 2014 study from the University of Washington.

There are no at-home tests—or any tests for that matter—that can definitively diagnose psoriatic arthritis. Lab tests are typically used to exclude other possible causes rather than confirm psoriatic arthritis.

With that being said, you can seek appropriate treatment if you are able to recognize the signs and symptoms of the disease, namely:

  • Painful, swollen joints typically affecting the ankle, knee, fingers, toes, or lower back
  • Joint stiffness, especially in the early morning or after a period of rest (similar to osteoarthritis)
  • Reduced range of motion
  • Swelling of the tips of the fingers (similar to gout)
  • Sausage-like fingers or toes (dactylitis), typically occurring along the entire length of the fingers or toes rather than a single digit
  • Tendon or ligament pain (enthesitis), often occurring at the Achilles tendon, the bottom of the foot (plantar fasciitis), or elbow (tennis elbow)
  • Skin rashes (plaques) that are characteristically dry, thick, red, and covered with silvery-white scales
  • Nail changes, including dents, ridges, lifting (onycholysis), thickening (hyperkeratosis), crumbling, and discoloration
  • Persistent fatigue, common with inflammatory autoimmune diseases
  • Eye problems, including uveitis and conjunctivitis (pink eye) caused by the effects of psoriasis on the eyelid
  • Psoriatic flares, in which disease symptoms spontaneously appear or worsen and just as suddenly resolve

Labs and Tests

When diagnosing psoriatic arthritis, blood tests are primarily used to rule out other types of arthritis, most especially rheumatoid arthritis. Although rheumatoid arthritis and psoriatic arthritis are both autoimmune diseases, rheumatoid arthritis directly attacks joint tissues. With psoriatic arthritis, joint damage is an indirect consequence of inflammation.

Tests your rheumatologist may order include:

  • Rheumatoid factor (RF): A negative or low level of rheumatoid factor may indicate psoriatic arthritis. Rheumatoid factor is found around 80% of people with rheumatoid arthritis. Low levels are present in 5% to 16% of people with psoriatic arthritis.
  • Anti-cyclic citrullinated peptide antibodies (anti-CCP): Once thought to be specific to rheumatoid arthritis, anti-CCP is also present in about 5% of people with psoriatic arthritis.
  • Inflammatory markers: Blood tests like erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) are used to measure systemic (whole-body) inflammation. These may be elevated in people with psoriatic arthritis but to a far lesser degree than occurs with rheumatoid arthritis.

Imaging

Diagnostic images, including X-ray and magnetic resonance imaging (MRI) scans, can be useful in the diagnosis of psoriatic arthritis. X-rays are able to detect bone resorption (the breakdown of bone mineral), while MRIs are better able to characterize soft tissue damage, including cartilage loss or the buildup of fibrous tissues (pannus) around an injured joint.

According to Kelley's Textbook of Rheumatology, around 77% of people with psoriatic arthritis will have joint abnormalities on X-ray. Moreover, 47% of those newly diagnosed will develop bone erosions within two years.

Characteristic features of psoriatic arthritis observed on X-ray or MRI include:

  • Asymmetric joint involvement, as opposed to symmetrical joint involvement with rheumatoid arthritis
  • Distal joint involvement (meaning those closest to the nail) of the fingers or toes
  • Entheseal involvement (meaning the connective tissue between a tendon or ligament and bone)
  • Asymmetrical spinal involvement, as opposed to the symmetrical involvement of ankylosing spondylitis
  • "Pencil-in-a-cup deformity" in which the tip fo the finger looks like a sharpened pencil and the adjacent bone has been worn down into a cup-like shape

Differential Diagnoses

Because there are no lab or imaging tests that can definitively diagnose psoriatic arthritis, the diagnostic process is ultimately one of exclusion.

The differential diagnosis typically involves a battery of tests that can accurately diagnose other common joint disorders. If the test is negative, that disorder can be removed from the list of possible causes.

Some of the more common differential diagnoses include:

  • Rheumatoid arthritis, differentiated with an RF factor blood test, hand X-rays, and symmetrical joint involvement
  • Gout, differentiated by the presence of uric acid crystals in synovial joint fluid
  • Osteoarthritis, differentiated by the lack of inflammation on either the ESR or CRP as well as a "gull-wing deformity" on X-ray (in which the central portion of a bone is worn down)
  • Ankylosing spondylitis, differentiated by the inflammation of the sacroiliac joint and the ilium as observed on an MRI
  • Reactive arthritis, differentiated by soft tissue swelling mainly on weight-bearing joints
  • Mycobacterial tenosynovitis, a bacterial infection differentiated by lab cultures
  • Sacroid dactylitis, a complication of sarcoidosis differentiated by the appearance of bone cysts on X-ray and granulomas (granular deposits) on tissue biopsies

A Word From Verywell

Psoriatic arthritis is a painful, progressive illness, and, without proper treatment, can lead to disability and a reduced quality of life. If you think you may have psoriatic arthritis, speak to your doctor and start treatment as soon as possible. Early treatment almost invariably confers to better long-term results. If left untreated, the damage caused to joints may be irreversible and require more invasive treatments, including surgery.

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Article Sources

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  2. Merola JF, Espinoza LR, Fleischmann R. Distinguishing rheumatoid arthritis from psoriatic arthritis. RMD Open. 2018;4(2):e000656. doi:10.1136/rmdopen-2018-000656

  3. Mclaughlin M, Ostör A. Early treatment of psoriatic arthritis improves prognosis. Practitioner. 2014;258(1777):21-4, 3.

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