New staging assists proper diagnosing of psoriatic arthritis

Psoriatic arthritis (PsA) is a unique form of inflammatory arthritis that occurs in patients with psoriasis, usually manifesting itself well after the skin lesions of psoriasis appear.

It's estimated prevalence ranges from 6 percent to 39 percent.

Over the past two decades, evidence has accumulated that PsA is a severe disease in at least 20 percent of patients with progression of joint damage, culminating in a destructive arthritis, and over half will have evidence of deforming arthritis.

Predictors for disease progression include polyarticular presentation, as well as the degree of joint inflammation.

As it is not as well recognized as other forms of the disease such as rheumatoid arthritis (RA) or osteoarthritis (OA), it is likely underdiagnosed, making it more difficult for physicians to launch a more effective treatment management, according to Philip J. Mease, M.D., chief of the Seattle Rheumatology Associates and the Division of Rheumatology Clinical Research at Swedish Hospital Medical Center, Seattle.

"A higher prevalence of PsA is documented when the disease is assessed in psoriasis-specific populations, especially those with more severe disease, whereas lower prevalence is documented in large population surveys, which include patients with psoriasis of low severity," Dr. Mease tells Dermatology Times. "A difficulty with accurate determination of prevalence from large population cohorts is that the diagnosis may be overestimated, for example, if a psoriasis patient with concomitant osteoarthritis or RA is mistakenly categorized as having PsA. Conversely, the disease may be underestimated if a psoriasis patient with PsA receives instead a diagnosis of osteoarthritis - a disease better-known to primary physicians."

TIMELY DIAGNOSIS

Most specialists would agree that patients suffering from PsA would greatly benefit from a timely diagnosis.

According to Dr. Mease, radiographic progression has been noted within two years of onset of PsA, with patients suffering from reduced quality of life and function. Management of the disease should be focused on controlling patients' symptoms as well as preventing the progression of damage. Initiating a therapy strategy can be done when the diagnosis is met, and this, therefore, adds urgency in establishing classification criteria that best recognize patients who develop PsA.

In the past, Moll and Wright criteria have been used for the classification of PsA. According to these criteria, PsA is present when a patient with psoriasis has an inflammatory form of arthritis, negative rheumatoid factor and one of the five distinct clinical subsets:

1. oligoarticular (< five tender and swollen joints) asymmetric arthritis

2. polyarticular arthritis

3. distal interphalangeal joint predominant

4. spondylitis predominant

5. arthritis mutilans.

Several other classifications have emerged since Moll and Wright with varying success.

CASPAR STUDY GROUP

Dr. Mease is part of the Classification Criteria for Psoriatic Arthritis (CASPAR) study group, which recently developed and put forth a new classification criteria based on an extensive analysis of more than 500 patients with PsA and 500 patients with another inflammatory arthritis serving as controls, named the CASPAR criteria.

The CASPAR criteria consist of established inflammatory articular disease with at least three points of the following features:

Dr. Mease says, "The new classification criteria continue to rely on the physician's clinical judgment regarding the presence of an inflammation condition in joints, spine and/or enthesium - sites of tendon, ligament and joint capsule fiber attachment to bone. Clues such as number and distribution of sites of involvement, presence of erythema, warmth and swelling, prolonged stiffness - especially in the morning - pain severity and constitutional features such as fatigue can be very helpful in confirming the diagnosis."