How Psoriatic Arthritis Is Diagnosed

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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. 

When diagnosing psoriatic arthritis, the focus is on distinguishing it from other types of arthritis, such as gout, rheumatoid arthritis, or osteoarthritis.

A diagnosis is made based on your medical history, physical examination, and X-rays or other imaging studies which look for evidence of joint damage caused by inflammation. Blood tests and synovial fluid analysis may be used to rule out other types of arthritis.  

Different types of arthritis respond better to some medications than others. Getting an accurate diagnosis is important for finding the best treatment for you, so you can maintain an active lifestyle and prevent disability.

At-Home Screening

Psoriatic arthritis has two main components, psoriasis and arthritis. Your doctor will take a detailed medical history and perform a physical examination.

Psoriasis causes raised, red scaly patches typically on the outside of elbows, knees, or scalp, although lesions can appear on any part of the body. Rashes are itchy, may burn or sting, and do not resolve with topical other-the-counter treatments. 

People with psoriasis are more likely to develop psoriatic arthritis. If you have psoriasis and wonder if you may be developing psoriatic arthritis, take this five-question quiz from the National Psoriasis Foundation.

The arthritis component of psoriatic arthritis can include inflammation in the joints, spine, or connective tissue (entheseal). Swelling of a whole digit, known as dactylitis, is a common symptom.

One feature that differentiates this type of arthritis from other inflammatory diseases is the involvement of fingernails and toenails. Psoriatic nail dystrophy, which may include pitting, separation of the nail from the nail bed (onycholysis), and thickening of the nail (hyperkeratosis).

Labs and Tests

When diagnosing psoriatic arthritis, blood work is typically taken to rule out other forms of arthritis. Tests your rheumatologist may order include; 

  • Rheumatoid factor: A negative or low-level of rheumatoid factor may indicate psoriatic arthritis. Rheumatoid factor is typically found in patients with rheumatoid arthritis, however low levels are present in 5 percent to 16 percent of psoriatic arthritis patients.
  • Anti-CCP: Another test used to rule out rheumatoid arthritis is cyclic citrullinated peptide antibodies (anti-CCP). These were once thought to be specific to rheumatoid arthritis but are present in about 5 percent of psoriatic arthritis patients.
  • Acute phase reactants: sedimentation rate, C-reactive protein [CRP], and serum amyloid A may be elevated in patients with psoriatic arthritis, but to a lesser degree than occurs with rheumatoid arthritis.

Imaging

Diagnostic images, including X-ray and magnetic resonance imaging (MRI) scans, can be helpful in diagnosis psoriatic arthritis.

According to Kelley's Textbook of Rheumatology, approximately 77 percent of patients with established psoriatic arthritis have abnormalities on X-ray. About 47 percent of patients with new or recent onset psoriatic arthritis develop erosions within two years. Distinctive features observed on X-ray that define the type of psoriatic arthritis include:

  • Asymmetric joint involvement
  • Involvement of interphalangeal joints of the fingers or toes
  • Involvement of entheseal (connective tissue) sites
  • Spinal involvement (less severe and asymmetric compared to ankylosing spondylitis)   

Generally, the radiographic (X-ray) progression of psoriatic arthritis in its early stages occurs slowly. Aside from the typical involvement of the spine and interphalangeal joints of the fingers and toes, psoriatic arthritis typically affects the large joints of the body.

Differential Diagnoses

Psoriatic arthritis takes on a few different forms, based on symmetry, areas of the body affected, and prognosis.

Symmetric Psoriatic Arthritis affects joints on both sides of the body (e.g., both knees, both hips), and usually affects multiple joints (polyarthritis). It is similar to rheumatoid arthritis but is typically milder. About 25 percent of psoriatic arthritis patients have this type.

Asymmetric Psoriatic Arthritis does not affect the same joints on both sides of the body. Any joint can be affected, though. A sausage-like appearance of fingers and toes is common. Joints may be red, warm, swollen, and painful. Generally considered a mild form of psoriatic arthritis, it may become disabling in some people. About 80 percent of people with psoriatic arthritis are affected by this type.

Distal Interphalangeal Predominant (DIP) Psoriatic Arthritis is considered the "classic type," according to the National Psoriasis Foundation, although it occurs in only about 5 to 10 percent of those with psoriatic arthritis. This type primarily involves the distal joints of fingers and toes (the joint closest to the nail), and may alter the appearance of fingernails and toenails.

Spondylitis Type of Psoriatic Arthritis primarily affects the spine. Between 5 percent and 20 percent of people with psoriatic arthritis have this type and about half of those with spondylitis are positive for the genetic marker HLA-B27.

Arthritis Mutilans Type of Psoriatic Arthritis is a severe, disabling, and rare form that affects less than 5 percent of people with psoriatic arthritis. The arthritis mutilans type is characterized by joint deformity with the small joints of the hands and feet most impacted. Neck pain and low back pain are also associated with this type of psoriatic arthritis.

A Word From Verywell

Psoriatic arthritis is a painful, progressive illness, and without proper treatment, could lead to a reduced quality of life and disability. If you think you may have psoriatic arthritis, speak to your doctor and start treatment as quickly as possible. With the right combination of medications and therapy, the disease can be managed and you can maintain a healthy, active lifestyle.

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