Juvenile idiopathic arthritis, the most common type of arthritis in kids and teens, comprises seven sub-types: oligoarthritis, polyarthritis (RF-positive and RF-negative), systemic, psoriatic arthritis (PsA), enthesitis-related, and undifferentiated.
In the United States, juvenile arthritis occurs in an estimated 20 to 45 children per 100,000 children. Of those children who develop juvenile arthritis, as many as 5 percent have PsA, making it relatively rare. In fact, PsA is one of the least common categories of juvenile arthritis, explains Pamela Weiss, M.D., associate professor of pediatrics and epidemiology at Perelman School of Medicine at the University of Pennsylvania, and attending physician and clinical research director of the Division of Rheumatology at Children’s Hospital of Philadelphia in Pennsylvania.
Why certain juvenile patients develop PsA is a question that is still being researched, although genetics may play into the risk factors. “More than half of children with psoriatic arthritis have at least one family member affected by psoriasis,” says Dr. Weiss. Genetic studies have shown associations with certain genes, she says, although these genetic associations are not used to guide diagnosis or therapy in clinical practice.
Up to one-third of adults with psoriasis may develop PsA, but estimates of risk in children with psoriasis are lacking.  “Signs of inflammatory joint disease (arthritis) in children may include stiffness in the mornings that gets better with activity, swollen or puffy joints, fingers or toes that look like sausages,” says Dr. Weiss. “Onset of psoriatic arthritis seems to be most common during the toddler years or during early adolescence. It is slightly more common in girls than boys.”
Diagnosing and Treating PsA
While there are no tests that can diagnose PsA, Dr. Weiss explains that the diagnosis is primarily clinical, making a physical exam by a rheumatologist key. In addition to doing basic blood counts, chemistries and inflammatory markers, rheumatologists check antinuclear antibodies (ANA) and human leukocyte antigen (HLA-B27), which may be indications that a person with PsA is at increased risk of developing associated eye inflammation or lower back arthritis.
“If the ANA is positive, that means that the risk of developing associated eye inflammation is higher. If the HLA-B27 is positive, that means that the risk of developing arthritis of the lower back is higher,” says Dr. Weiss.
Many times, treatment of PsA in pediatric patients requires a collaborative team of health care professionals, including “frequent visits to the rheumatologist (for the joint disease), an ophthalmologist (to monitor for and/or treat any associated eye inflammation) and a dermatologist (for the skin disease). Physical and/or occupational therapists may also be involved,” she says.
The treatment depends on the PsA severity. “If only a few joints are involved, then localized therapy via joint injections (steroid delivered to the swollen joint via needle) is an option that provides quick results,” says Dr. Weiss.
For more severe cases, treatment may consist of systemic therapies. These types of treatment work throughout the body and can include oral systemics and biologics. “If several joints and/or the eyes are involved, then systemic therapy is typically recommended,” she says.
While methotrexate is the most common initial therapy, biologics (most commonly tumor necrosis factor inhibitors) may also be discussed for some children. More treatments are available now for pediatric PsA than ever before, a trend that shows no signs of slowing. “There are also several targeted drugs for psoriatic arthritis that are still being studied in children that hold a lot of promise,” says Dr. Weiss.
Patients should check in with their rheumatologist and eye doctor regularly, recommends Dr. Weiss. “Exercise and stretching are also helpful to maintain joint health,” she adds. “[In addition] there are many ‘diets’ that parents ask me about. However, I am generally not a fan of restricting a child’s diet as that can be somewhat traumatic, especially after a new diagnosis. Omega-3 fatty acids have been shown to have some benefit, but consistently taking any prescribed medication by the rheumatologist is more important.”
Early recognition, diagnosis and treatment of PsA is crucial. Evidence has shown that delaying treatment by as little as six months can result in permanent joint damage. Without a diagnostic test, however, reaching a diagnosis can be challenging. That is why the National Psoriasis Foundation launched the PsA Diagnostic Test Grant. Six first-year proof-of-concept proposals that have the potential to achieve this goal within five years have been funded.