Causes and Risk Factors of Psoriatic Arthritis

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Psoriatic arthritis is a type of arthritis linked to the autoimmune disease psoriasis. It can occur on its own but is usually preceded by psoriasis in around 84 percent of cases, according to a 2014 review of studies in Psoriasis Forum.

Psoriatic arthritis is characterized by joint pain and swelling as well as the restriction of joint movement. It is similar in appearance to rheumatoid arthritis but tends to affect the feet, lower back, fingers, and toes in ways that rheumatoid arthritis doesn't. As a progressive disease, psoriatic arthritis can cause permanent joint damage and the loss of mobility if left untreated.

Although the underlying mechanisms of psoriatic arthritis remain unknown, scientists have able to identify certain commonalities that define the disease. These include immunologic, genetic, and environmental risk factors that appear to determine who gets the disease and how severely.

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. Though both are considered autoimmune in origin, rheumatoid arthritis is characterized by a direct immune assault on the joint tissues, causing inflammation and progressive damage.

Psoriatic arthritis works differently. In this instance, the inflammation is spurred by psoriasis, a disease which targets skin cells rather than joint tissues. The inflammation caused by the autoimmune assault can affect more than just the skin. Over time, other organ systems may be affected, including the eyes, nails, brain, kidneys, and joints.

Psoriatic arthritis is the consequence of the inflammatory damage induced by psoriasis. This can occur even if there are no outward signs of psoriasis. Psoriatic arthritis cannot occur unless psoriasis is there to drive the disease.

Genetics

Why autoimmune diseases occur remains something of a mystery. Under normal circumstances, a type of white blood cell known a T-cell activates when confronted with a harmful agent and disperses inflammatory proteins (called cytokines) to neutralize the threat. Once neutralized, other chemicals (such as itaconic acid) will be dispersed to "turn off" the inflammation.

With psoriatic arthritis and other autoimmune diseases, both of these processes are flawed. Not only will the immune system misdirect the assault, but the ensuing inflammation will continue unabated to reap havoc until anti-inflammatory treatments can stop it.

Genetics is almost certainly the underlying cause of 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 "more highly heritable" autoimmune diseases.

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

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 of which 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.

Despite the association, having these or other high-risk mutations does not mean you will get psoriatic arthritis. It appears that environmental triggers are needed to "switch on" the disease in those with a genetic predisposition.

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, cigarettes were 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 in play, including increased cytokine production, delayed hypersensitivity reactions, or changes in phosphorus or calcium levels. Scientists continue to search for clues.

A Word From Verywell

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

Reducing stress, avoiding alcohol and smoking, maintaining a healthy weight, and engaging in moderate, low-impact exercises are just some of the ways to prevent flares and protect the health of your joints.

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