Causes and Risk Factors of Psoriatic Arthritis

Psoriatic arthritis is a type of arthritis linked to psoriasis, and it is associated with immunologic, genetic, and environmental risk factors.

As a progressive disease, psoriatic arthritis can cause permanent joint damage and reduced mobility if left untreated. It can occur on its own but is usually preceded by psoriasis in around 84% of cases, according to a 2014 review of studies in Psoriasis Forum.

Immunologic Causes

Psoriatic arthritis is classified as inflammatory arthritis, meaning that the joint damage is the direct result of intense, chronic inflammation.

This differs from osteoarthritis in which the damage is due to structural wear and tear.

Psoriatic arthritis also differs from rheumatoid arthritis (RA), though both are considered autoimmune in origin.

Genetics

Why autoimmune diseases occur remains something of a mystery. Under normal circumstances, T-cells, which are a type of white blood cell (WBC) are activated in response to threats like viruses or cancer cells. This leads to the dispersal of inflammatory proteins (cytokines) that help neutralize the threat. Once the threat is resolved, other chemicals (such as itaconic acid) are released to subdue the inflammation.

With psoriatic arthritis and other autoimmune diseases, these processes are flawed. The immune system is misdirected, and the ensuing inflammation continues to reap havoc—often until anti-inflammatory treatments stop it.

Genes play a role in this dysfunction. This is evidenced in part by the pattern of inheritance seen among family members. In fact, psoriatic arthritis is considered one of the more highly heritable autoimmune diseases.

According to a 2010 review from the University of Toronto:

• You are 55 times more likely to get psoriatic arthritis if a first-degree family member (parent or sibling) has it.
• Around 23% of non-identical twins will both have the disease, while as many as 70% of identical twins will both be affected.

When looking at the genes themselves, there is not yet a single pattern that independently describes psoriatic arthritis. With that being said, there are certain gene mutations more commonly found in people with psoriatic arthritis than those without it.

Chief among these are mutations of the human leukocyte antigen (HLA), a protein found on cells that the immune system uses to target attacks. One such example is HLA-B27, the mutation that has the highest predictive value for psoriatic arthritis (especially psoriatic arthritis of the spine).

Other HLA antigens, including HLA-B13, HLA-B17, HLA-B57, and HLA-Cw*0602, occur more frequently in people with psoriatic arthritis than in the general population.

Lifestyle Risk Factors

There is a long list of possible triggers for psoriatic arthritis, which can vary from person to person. Many of these are problematic for all types of psoriatic disease; others are more specific to psoriatic arthritis.

Smoking is one such example. According to a 2018 study in the Annals of Rheumatic Diseases, smoking cigarettes was associated with an increased risk of psoriatic arthritis when compared to the general population but a decreased risk among people with psoriasis.

Other triggers closely linked to psoriasis include:

• Extreme emotional stress
• Excessive alcohol intake, especially non-light beer
• Cold, dry weather
• Certain medications, including beta-blockers, antimalarials, lithium, quinidine, and indomethacin
• Skin infections, particularly Staphylococcal aureus and Streptococcal epidermidis

Moreover, any stress you place on a joint can trigger symptoms. This includes the stress induced by obesity or lifting a heavy weight. Even an accidental blow to a joint can trigger an acute flare.

According to a 2011 study in Arthritis Care and Research, people with psoriasis who lifted more than 100 pounds per hour were three times more likely to develop psoriatic arthritis than those who didn't. A prior joint injury more than doubled the risk.

How these triggers induce acute flares is still unknown. It is possible that different mechanisms are at play, including increased cytokine production, delayed hypersensitivity reactions, or changes in phosphorus or calcium levels. Scientists continue to search for clues.

While many of the risk factors for psoriatic arthritis are not modifiable, there are things you can do to better manage the disease. Speak with your healthcare provider or rheumatologist about medications and lifestyle changes that can help you slow progression and maintain an optimal quality of life.