WAIKOLOA, HAWAII – Joint pain arising in a patient with psoriasis is by no means necessarily due to psoriatic arthritis.
Psoriasis patients can get osteoarthritis or rheumatoid arthritis, just like individuals without the skin disease. The distribution pattern of affected joints provides a useful guide as to which arthropathy is involved.
"When a patient who’s got psoriasis comes to me and says, ‘I have a tremendous amount of joint pain,’ the first place I look is the heel. Heel involvement doesn’t happen very often in rheumatoid arthritis. If the heel hurts, it’s probable that the patient has dactylitis and some form of psoriatic arthritis," according to Dr. Daniel E. Furst, the Carl M. Pearson professor of rheumatology at the University of California, Los Angeles.
Another useful clue: Psoriatic arthritis often affects the distal phalangeal joints of the fingers and toes, with accompanying characteristic psoriatic nail changes, but it spares the metacarpophalangeal (MCP) joints. In contrast, MCP involvement is a typical feature of rheumatoid arthritis, he explained at the Hawaii Dermatology Seminar sponsored by Skin Disease Education Foundation (SDEF).
"If only we understood why one joint tends to be affected and not another, we would sure know a whole lot more about psoriatic arthritis, and rheumatoid arthritis for that matter," Dr. Furst observed.
Involvement of the distal interphalangeal (DIP) joints is a common feature in osteoarthritis as well as psoriatic arthritis. However, psoriatic arthritis, unlike osteoarthritis, is an inflammatory arthritis. The affected fingers and toes in a patient with psoriatic arthritis often develop a painful, red, warm, sausage-like swelling of the soft tissue on the entire digit.
Bruce Jancin/Elsevier Global Medical News
Dr. Daniel Furst
"If there’s erythema and squishiness when you push on a painful joint, that’s synovitis, not osteoarthritis," the rheumatologist noted.
Also, osteoarthritis has a strong tendency to involve the carpometacarpal joint of the thumb, a site spared in psoriatic arthritis, he continued.
Psoriatic arthritis often first shows up as a monoarticular, asymmetric arthritis of a larger joint, such as the knee, ankle, or wrist. Rheumatoid arthritis tends to come on much stronger.
"In rheumatoid arthritis, it’s frequently all at once. The patient will say, ‘In a week I went from nothing to pain everywhere.’ Not so in psoriatic arthritis," according to Dr. Furst.
Spondyloarthropathy is common in psoriatic arthritis. It often takes the form of a spondylitis characterized by asymmetric thickening and calcification of the longitudinal ligaments of the spine, resulting in asymmetric syndesmophytes on imaging. The result is a painful and/or stiff low back.
Psoriatic arthritis is widely thought of as a rheumatoid factor–negative disease, but that’s not strictly true. Roughly 15% of psoriatic arthritis patients are rheumatoid factor–positive.
Differentiating psoriatic arthritis from other types of arthritis that occur in psoriasis patients is important from a treatment standpoint. Psoriatic arthritis causes much more bony destruction than recognized until fairly recently, twice as much as rheumatoid arthritis by some measures. The nonbiologic disease-modifying antirheumatic drugs are only marginally effective for joint disease in psoriatic arthritis patients, with the exception of leflunomide (Arava), which has fair benefit for the peripheral arthritis but less for the skin disease.
At present, the tumor necrosis factor (TNF) inhibitors are the most effective agents available for peripheral and axial joint disease in psoriatic arthritis. But the response can be less impressive than in patients with psoriasis-only or rheumatoid arthritis. New therapies on the horizon include agents targeting the inflammatory cytokines interleukins-6, -12, and -15, as well as orally administered small molecules that inhibit Janus kinase, spleen tyrosine kinase, TNF-alpha converting enzyme, or mitogen-activated protein kinase.
"There’s a lot of stuff coming down the pike, including new drugs which have mechanisms of action very different from those most extant in psoriasis. Some of it is going to work. But so far we really don’t know which of it will," Dr. Furst said.
He reported that he serves as a consultant to or recipient of research grants from more than a dozen pharmaceutical companies and the National Institutes of Health.
SDEF and this news organization are owned by Elsevier.