Dermatologists underestimate psoriatic arthritis incidence

National report - Dermatologists should be more diligent in asking psoriasis patients about symptoms of psoriatic arthritis, says Kenneth Gordon, M.D., associate professor of medicine, Loyola University, Chicago.

Many patients with psoriatic arthritis are candidates for biologic therapy that can inhibit progression of joint damage and deformity associated with the disease.

"I think we've done a much better job as dermatologists in the past five years trying to find out if patients have psoriatic arthritis, and this has made a big impact on our therapeutic decisions," he says.

Statistics

According to American College of Rheumatology (ACR) estimates, at least 15 percent of psoriasis patients will develop psoriatic arthritis and in 15 percent of these, arthritis symptoms may present prior to cutaneous disease.

However, in most patients psoriatic arthritis develops after cutaneous symptom onset and can occur as much as 10 years after cutaneous disease starts. Psoriatic arthritis can occur at any age including during childhood, but is most common between the ages of 30 and 50 years. It typically affects the fingers, wrists, back, pelvis and the large joints of the lower extremities.

Treatment options

The progression of psoriatic arthritis is not as well understood as that of rheumatoid arthritis and while many patients with mild psoriatic arthritis experience symptoms without long-term problems, many others will eventually have permanent deformities, Dr. Gordon says.

"In rheumatoid arthritis, methotrexate has been shown to slow the progression of the disease. But recently anti-TNF agents have been shown to be superior for disease modification. We don't know how well methotrexate works for delaying bone changes in psoriatic arthritis, but TNF inhibitors clearly can make a difference."

The monoclonal antibody anti-TNF agent infliximab has been shown to inhibit joint damage progression as well as manage cutaneous symptoms.

Infliximab is infused at a dose of 5 mg/kg at baseline and weeks two and six followed by every two months thereafter.

"After 10 weeks, about 80 percent of patients achieve Psoriasis Assessment Severity Index (PASI) 75," Dr. Gordon says. "It is a rapidly acting drug and within the first three months you get a maximal response."

Related research

Arthur Kavanaugh, M.D., University of California, San Diego, reported that phase 3 trial patients with active psoriatic arthritis reported a 48.6 percent improvement in physical functioning after 14 weeks infliximab treatment compared to an 18.4 percent physical functioning reduction among placebo patients.

In addition, after 24 weeks of treatment, 39 percent of patients achieved a PASI 90 response and 27 percent achieved an ACR 70 response indicating a 70 percent improvement in psoriatic arthritis symptoms.

After 50 weeks of treatment, patients showed a 1.8-point van der Heijde-Sharp score regression of joint damage from baseline indicating that treatment significantly inhibited progression of joint erosion and joint space narrowing.

Etanercept

Etanercept, the first biologic agent approved for psoriatic arthritis treatment, was also studied in patients with psoriasis and psoriatic arthritis.

At two years of treatment, 18 percent of patients achieved an ACR 70 response, 46 percent had an ACR 50 response and 63 percent showed an ACR 20 response, reported Mark Lebwohl, M.D., Mount Sinai School of Medicine, New York.

Etanercept also inhibited progression of joint erosion and joint space narrowing compared to placebo with etanercept-treated patients showing a 0.38-point van der Heijde-Sharp score regression of joint damage from baseline at two years.

"The incidence of psoriatic arthritis is often underestimated by dermatologists," Dr. Gordon says. "Patients reporting joint pain should be considered for aggressive therapy with disease modifying medications including biologics to prevent disease progression. "The anti-TNF agents are the drugs of choice for many patients with psoriatic arthritis."