Psoriatic arthritis (PsA) is a complex disease with many possible causes and risk factors. PsA is a form of inflammatory arthritis that occurs in up to one‐third of people with psoriasis, causing joint damage in any part of the body. PsA commonly causes dactylitis (severe inflammation of the finger and toe joints), enthesitis (inflammation where tendons and ligaments attach to the bone), and spondylitis (inflammation of the spine).
Psoriatic arthritis is an autoimmune disease, meaning the body’s immune system mistakenly attacks healthy cells and tissues, leading to damage and inflammation. In psoriatic arthritis, the immune system attacks the ligaments and joints, causing symptoms of psoriatic arthritis such as joint pain, stiffness, and swelling.
There is no known cause of psoriatic arthritis. However, rheumatologists and researchers believe psoriatic arthritis is triggered by a combination of biological and environmental factors.
Research has identified genetic factors associated with the development of psoriatic arthritis. Many of these genetic factors are involved in the abnormal function of the immune system. Activation of these genes is linked to joint inflammation, suggesting their role in PsA symptoms.
T cells, a type of immune cell, are heavily involved in psoriatic arthritis. These cells release proteins (called cytokines) that stimulate inflammation. This inflammation causes joint swelling, pain, and damage. Studies show that higher numbers or activity of these T cells and the cytokines they release are linked to PsA symptoms and severity. Several antirheumatic drugs work by turning down the immune response mediated by T cells and cytokines.
Many injectable drugs used in the treatment of psoriatic arthritis are inhibitors for immune mediators such as cytokines. For example, PsA drugs such as Humira (adalimumab), Enbrel (etanercept), and Remicade (infliximab) block the activity of a cytokine called tumor necrosis factor (TNF). By turning down the immune response mediated by TNF, these drugs ease PsA symptoms. Nonsteroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen, also work by reducing pain from immune-mediated inflammation.
Other environmental factors potentially involved in psoriatic arthritis include physical trauma, injuries, and work-related physical activities. The connection between injuries and trauma and the development of psoriasis and PsA is known as the Koebner phenomenon.
There are many risk factors for psoriatic arthritis. Although these risk factors have been associated with PsA, additional research is needed to determine why and how they contribute to disease.
Psoriasis, a skin condition characterized by scaly lesions, is the most significant risk factor for psoriatic arthritis. However, people without skin psoriasis can also develop psoriatic arthritis. Psoriatic arthritis affects nearly 30 percent of people with psoriasis. Psoriatic arthritis most commonly begins about 10 years after skin psoriasis. In approximately 10 percent to 15 percent of people, psoriatic arthritis begins before skin psoriasis.
Severe psoriasis may increase the risk of PsA more than mild or moderate psoriasis does. People with psoriasis lesions or plaques on their nails (nail pitting), scalp, or genital region are also more likely to develop PsA.
Psoriatic arthritis runs in families. Nearly 40 percent of people with psoriatic arthritis have a family member with psoriasis or arthritis. The data suggests that genetics play a role in the development of psoriatic arthritis.
White people are at an increased risk of psoriatic arthritis compared to other ethnicities.
Although researchers don’t yet understand why, some medical treatments have been linked to PsA, including:
Men and women are equally likely to develop psoriatic arthritis, so gender is not a risk factor. Although some studies have suggested a link between hormones and PsA, no definite connection has been proven.
PsA can occur at any age. Psoriatic arthritis usually appears between the ages of 30 and 50, although children with psoriasis are also at risk.
Other health and environmental factors can increase the risk of PsA, including:
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