If you have psoriasis, does that mean you’ll get psoriatic arthritis? Not necessarily.

Only about 30 percent of people with psoriasis develop psoriatic arthritis (PsA). PsA is an inflammatory arthritis that usually occurs in people between the ages of 40 and 50. However, it can affect both younger and older people as well.

PsA involves pain, stiffness, swelling, and tenderness of the joints, ligaments, and tendons on both sides of your body. PsA can also affect other areas, such as your eyes, heart, or stomach. As with psoriasis, PsA symptoms can come and go, and symptoms range from mild to severe.

Most people have psoriasis symptoms for an average of 10 years before they get PsA. But some people get PsA before they have the skin symptoms of psoriasis.

PsA is a progressive disease, with joint damage occurring early in the disease. During the first two years of PsA, up to 50 percent of people have joint erosion at a rate of 11 percent per year. In about 20 percent of people with PsA, the joint damage becomes disabling.

Initially, PsA was considered a variation of rheumatoid arthritis (RA). Now it’s seen as a separate condition. Most people with PsA don’t have the rheumatoid factor that’s present in people with RA.

PsA is under-diagnosed among people who have psoriasis. If you have any symptoms of PsA, it’s important to see your doctor. Early diagnosis and treatment for PsA are known to improve the disease outcome.

The causes of PsA are still largely unknown. It’s a complex disease and the subject of ongoing scientific studies. Also, PsA classification and diagnostic criteria aren’t uniformly accepted.

PsA is thought to be caused by a combination of genetic, environmental, and immunological factors:

Family history of psoriasis

Having a family history of psoriasis doesn’t guarantee that you’ll develop psoriasis or PsA.

But having a family history of psoriasis increases your risk of getting psoriasis and PsA. About 40 percent of people with psoriasis or PsA have a family member with psoriasis or PsA.

You’re three to five times more likely to inherit PsA than you are to inherit psoriasis, according to studies of people who have PsA. It’s thought that this is because there are genetic differences between people who have psoriasis and people who have PsA.

One study of identical twins with psoriasis found that when one twin had psoriasis, only 70 percent of the other twins developed psoriasis. The fact that 30 percent of identical twins didn’t get psoriasis indicates that factors other than genetics are involved.

Environmental factors

Many correlations have been observed between environmental conditions and PsA, but the exact mechanisms aren’t known.

Below are some of the reported correlations. Keep in mind that although these factors have been observed in research studies of people with PsA, they may not be causal.

Association with other diseases

Psoriasis is linked to other comorbidities such as cardiovascular disease. The exact mechanism of the connections isn’t fully understood but is widely researched. There are more studies of psoriasis cofactors than there are of PsA.

A 2012 study of women with psoriasis and other conditions found a high prevalence of these cofactors:

  • obesity
  • diabetes
  • hypertension
  • abnormal lipids

Obesity

People with PsA have an increased prevalence of obesity compared with the general population. Ongoing studies are investigating what metabolic mechanisms are involved.

A 2012 review reported that young people who are overweight have a three times greater risk for developing PsA. For each increase in body mass index (BMI), risk of PsA went up by 5.3 percent.

The same review reported on studies indicating that obesity had a negative effect on treatment for PsA. However, another study, reported in a 2012 review article, found no correlation between a larger waistline and the severity of PsA.

Gene variations

Gene variation in psoriasis and PsA is an ongoing research topic. It’s been found that psoriasis and PsA have different genes. This may explain why only some people with psoriasis develop PsA.

Some genes have been identified with different types of PsA and PsA involvement of particular joints. In the future, today’s genetic research should prove helpful for diagnosing and treating PsA.

In general, genetic studies are providing new ways of looking at psoriasis and PsA. A study reported in 2015 found about 60 genes that may be risk factors for psoriasis. About 10 of these genes are thought to predispose Caucasians to psoriasis, but the same genes don’t affect Asians.

This may explain the geographical differences of PsA. PsA incidence and prevalence are lower in Asia than in North America and Europe.

Immunology

The role of immunology in PsA and psoriasis is becoming better understood. PsA is thought to result when your body’s immune system is triggered in some way to mistakenly attack your healthy joints. The mechanism for this isn’t completely known.

In general, researchers are looking at the relationship of chronic inflammation to PsA and other diseases it’s associated with. Factors under investigation include:

  • higher levels of tumor necrosis factor-alpha
  • T helper cell type 1 and type 17, which are associated with immune response
  • nuclear factor xB, which is associated with immune system regulation
  • osteoclast activity (bone-reabsorbing cells)

Symptoms of PsA vary by individual. Symptoms also vary greatly, from mild to severe. They can start suddenly or slowly. Some general symptoms include:

  • fatigue
  • stiffness, swelling, or tenderness in joints
  • tendon inflammation or tenderness (enthesitis)
  • swollen fingers or toes (dactylitis)
  • foot pain in the heel or sole
  • pitted or separated nails (nail dystrophy)
  • eye redness and inflammation (uveitis)
  • reduced range of motion
  • inflammatory neck pain
  • inflammation of the vertebra (spondylitis)
  • inflammation of sacroiliac joints (sacroiliitis)

Your doctor will examine you and ask you about your medical history and that of your family.

They’ll ask about your symptoms, when they began, how long they last, and whether they’ve gotten better or worse.

PsA can be challenging to diagnose, because its symptoms resemble those of other diseases such as rheumatoid arthritis or gout. Also, in 10–15 of people, arthritis occurs before the appearance of psoriasis skin lesions.

The doctor may order X-rays, MRI, CT scans, sonography, or bone scintigraphy to check for bone involvement and to look at particular joints and tendons. They may also order blood tests to check for rheumatoid factor (RF), which usually isn’t present in people with PsA.

If you have psoriasis and you notice any symptoms of arthritis, you should see your doctor. If PsA is diagnosed and treated early, it has a better outcome. Current treatment and new treatments being developed may help slow joint deterioration.

You can’t change your family history, but there are some things you can change to reduce your risk of PsA:

  • lose weight if you’re overweight
  • stick to a healthy diet
  • keep active
  • try to limit stress

See a counselor or therapist to talk about coping with stress. You may want to consider joining an online psoriasis/PsA support group. (See https://www.psoriasis.org/navigationcenter.) The National Psoriasis Foundation also offers a “navigation” service with free help for you or a family member.