Psoriatic arthritis (PsA) is a unique inflammatory condition that occurs in up to 40% of people with psoriasis.1,2 Psoriasis is an inflammatory disease that affects the skin, causing red, scaly patches that are often painful and itchy. Both conditions are chronic, lifelong diseases, although symptoms may come and go over time. In the majority of cases, the skin disease (psoriasis) precedes joint disease (psoriatic arthritis), and PsA often develops within 5-10 years from the onset of psoriasis. However, in about 10-15% of patients, PsA will develop before psoriasis. 1
Symptoms of psoriatic arthritis
Psoriatic arthritis is highly variable, presenting with different patterns in different patients. 3 The most common symptoms of psoriatic arthritis include:
- Swelling, stiffness, redness, and/or heat at the joints
- Inflammation and pain at the attachment points of ligaments and tendons
- Joint pain
- Changes to nails
- Loss of normal functions, such as daily tasks of grooming or shopping 1,2
PsA can affect the joints in an asymmetrical pattern, not necessarily in the same joints on both sides of the body. PsA generally presents as mild disease affecting only a few joints, however, over time it may affect multiple joints and can cause disfigurement. 2 The disease is highly variable and progressive: some patients have a mild, nondestructive type, while others develop progressive joint damage. 3 PsA is severe in at least 20% of people living with the disease. 2
Differences between psoriatic arthritis and rheumatoid arthritis
Although some characteristics of PsA resemble those of Rheumatoid Arthritis (RA), PsA can be distinguished from RA by several features. While RA occurs more commonly in women, PsA occurs just as frequently in both men and women. The distal joints affected in PsA often occur so that all the joints in a single digit (finger or toe) are affected, rather than fewer but symmetrical joints on both sides of the body which is more characteristic of RA. The degree of redness over the affected joints, the presence of spinal involvement, and the presence of enthesitis (inflammation at the attachment of tendons or ligaments) are typical features of PsA.2
Patterns of psoriatic arthritis
Psoriatic arthritis is characterized by five clinical patterns:
- Distal interphalangeal predominant pattern – primarily affecting the joints closest to the nails in the fingers and toes
- Oligoarticular asymmetrical – only a few joints are affected, and not matching on both sides of the body
- Polyarticular RA-like – multiple joints are affected with similar characteristics to Rheumatoid Arthritis
- Spondylitis – affecting joints and the points where ligaments and tendons attach muscle to bone
- Arthritis mutilans – severe form of the disease causing deformity of the hands, fingers, or toes 2,4
What causes psoriatic arthritis?
The exact cause of PsA is unknown, although researchers have discovered a genetic component. Those with a first-degree relative with PsA are at greater risk of developing the disease. Scientists have also found several genetic markers that impact the inflammatory response in people with PsA.1,5
Another factor in the causation of PsA is environmental factors. In people with the genetic component for PsA, the disease is often triggered by something in the environment, such as physical trauma or a bacterial or viral infection. 5
How is psoriatic arthritis diagnosed?
Patients who present with characteristics of PsA, particularly the pain, swelling, tenderness and stiffness in the distal joints and the inflammation of the tendons and ligaments in the joints, should be further evaluated. Physicians most often use the CASPAR criteria (Classification Criteria for Psoriatic Arthritis).
However, PsA is often undiagnosed or misdiagnosed, and there is no definitive test for PsA.1,6 Up to 15% of people living with psoriasis have undiagnosed PsA. 7 Because treatment not only helps manage painful symptoms but also can slow the potential disfiguring progression of the disease, early diagnosis is critical.1