Psoriatic arthritis (PsA), also called psoriatic spondylitis, is a type of inflammatory arthritis. It affects about one-third of people with psoriasis. It’s different from rheumatoid arthritis, but like that condition, PsA causes joint pain and inflammation throughout the body. Although the exact causes of PsA are not fully known, researchers have identified several genetic and environmental risk factors.

What Causes Psoriatic Arthritis?

PsA is an autoimmune disease, which means the body’s immune system mistakenly attacks healthy cells and tissues as if they were harmful viruses or bacteria. In PsA, the immune system targets the ligaments and joints, causing inflammation and damage.

PsA is part of a family of related autoimmune disorders called spondylitis or spondyloarthritis.

The exact cause of psoriatic arthritis is not understood. However, rheumatologists (doctors who specialize in bones, muscles, internal organs, and joints) and researchers believe that a combination of biological and environmental factors can trigger the condition.

Genetic Causes

Research has identified genetic factors linked with the development of psoriatic arthritis. Like other types of spondyloarthritis, PsA has been linked to specific variations on certain inherited genes, such as HLA-B27, which are involved in the immune system. Researchers have identified several genes linked to the development of PsA.

Immune System Involvement

An abnormal immune response is responsible for causing symptoms of all types of inflammatory arthritis. This can involve a variety of inflammatory mediators (substances in the body that promote inflammation).

T cells, a type of immune cell, play a major role in PsA. These cells release proteins called cytokines — chemical messengers that either trigger inflammation or protect you from it. In people who are genetically prone to PsA, these cells release more proteins that trigger inflammation. This inflammation causes joint swelling, pain, and damage. Studies show that higher numbers or increased activity of T cells and cytokines are linked to PsA symptoms and severity.

Environmental Causes

Research has found that some environmental factors can play a role in the development of psoriatic arthritis. Below are some key factors that may contribute to PsA.

Infections

Studies have found that certain infections may contribute to PsA. Infection with the bacteria Streptococcus pyogenes, which causes strep throat, seems to correlate with increased PsA risk. Other infections believed to trigger PsA include the sexually transmitted disease chlamydia and the bacteria that cause infectious diarrhea, including species of Campylobacter and Yersinia.

Several viral infections may possibly be linked to PsA, including HIV and hepatitis C. Viruses believed to cause rheumatoid arthritis may also cause PsA, including parvovirus B19, cytomegalovirus, and Epstein-Barr virus.

Physical Trauma, Injuries, and Work-Related Physical Activities

Physical trauma or injuries, like scratches, can also trigger PsA. People with psoriasis may experience what is known as the Koebner phenomenon (also called Koebnerization). This phenomenon causes new skin lesions to appear at the site of skin injuries like scratches, cuts, or burns. In people with PsA, even minor injuries can trigger a mild immune response, which could cause new lesions to appear.

In people with PsA, the Koebner phenomenon also appears to impact tissues such as tendons. This may explain how work-related PsA develops. Research has found that people who work in jobs that involve repeated heavy lifting (100 pounds per hour or more) and pushing heavy loads (more than 200 pounds per hour) are more likely to develop PsA.

What Are the Risk Factors for Psoriatic Arthritis?

There are many risk factors associated with PsA. Although more research is needed to fully understand these risk factors, the following have been found to increase a person’s likelihood of developing PsA.

Psoriasis

Psoriasis is a skin condition characterized by scaly lesions (plaques). Having psoriasis is the most significant risk factor for PsA. However, people without skin psoriasis can also develop PsA. According to the National Psoriasis Foundation, PsA develops in about 30 percent of people with psoriasis, often around 10 years after skin symptoms first appear. In 15 percent to 20 percent of cases, PsA symptoms begin before the skin condition develops.

People with more severe psoriasis have a higher risk of PsA. People with psoriasis lesions or plaques on their scalp, genital region, or nails (nail pitting) are also more likely to develop PsA.

Family History

PsA runs in families. According to Cleveland Clinic, about 40 percent of people with PsA have a family member with psoriasis or arthritis. Combined with the known association between PsA and certain inherited genes, this supports the assertion that genetics plays a significant role in the development of PsA.​

Race and Ethnicity

PsA is significantly more common in white people, according to the Arthritis Foundation. However, studies have shown that Asian and Hispanic people tend to have more extensive and severe PsA. Additionally, research published in the International Journal of Rheumatic Diseases found that Pakistani populations have an even higher risk of developing PsA based on family history than their white counterparts.

Sex

PsA can affect anyone, regardless of sex. Some studies have suggested a link between female hormones and PsA, but no definite connection has been proven.

Age

PsA can occur at any age, but it usually develops between the ages of 30 and 50. Children with psoriasis are also at risk of developing PsA. Most people who are diagnosed with skin psoriasis develop PsA in 10 to 20 years.

Other Environmental Factors

Other environmental risk factors among people with psoriasis include infections that require antibiotics and work that involves repeatedly moving heavy loads.

What Triggers Psoriatic Arthritis Flares?

Some factors can trigger flares or flare-ups of psoriatic arthritis. A flare-up is a worsening of PsA symptoms.

Common flare triggers include:

• Infections
• Physical injuries, including sunburns
• Skipping or stopping your PsA medications
• Excess stress
• Unhealthy and inflammatory foods

Identifying your PsA flare triggers, in addition to consulting a rheumatology provider for treatment, can help you manage your condition more effectively and reduce flare-ups.

Talk With Others Who Understand

MyPsoriasisTeam is the social network for people and their loved ones with psoriasis and psoriatic arthritis. More than 131,000 members come together to ask questions, give advice, and share their stories with others who understand life with psoriasis and psoriatic arthritis.

Do you have psoriatic arthritis? What factors have contributed to your condition? Share your experience in the comments below, or start a conversation by posting on your Activities page.