Examining the Prevalence of Undiagnosed Psoriatic Arthritis

A review and meta-analysis of a dozen studies indicates that more than 10% of all psoriasis patients have undiagnosed cases of psoriatic arthritis.

Researchers from several French institutions began by searching PubMed, Cochrane and Embase and reviewing 394 studies. None of them explicitly attempted to quantify the prevalence of undiagnosed psoriatic arthritis among psoriasis patients, but 7 epidemiological studies and 5 studies of arthritis screening tools provided the necessary data.

The rate of undiagnosed arthritis varied enormously among the psoriasis patients in the different study groups, ranging from a low of 4% to a high of nearly 34%. The meta-study authors attributed the variance, in large part, to the very different criteria the underlying studies used to diagnose psoriatic arthritis.

The high degree of heterogeneity (I² = 96.86%) led the study team to use a random effects model to estimate how common undiagnosed cases of psoriatic arthritis are among the general population of psoriasis patients. The combined results of all the studies produced a final estimate of 15.5%. The combined results of just the epidemiological studies produced a final estimate of 10.1%.

Even the lower number suggests a major opportunity for improving the management of psoriatic arthritis by means of early diagnosis and treatment. “The high prevalence of undiagnosed psoriatic arthritis in patients with psoriasis adds to the recommendation that dermatologists need to screen all patients with psoriasis for psoriatic arthritis,” the study authors wrote in the Journal of the American Academy of Dermatology.

Only about 1 in 4 psoriasis patients will ever develop psoriatic arthritis, but research has yet to uncover how and why the first disease leads to the second, so there’s no way to tell which patients will fall victim. As a result, guidelines recommend that all people with psoriasis be screened for psoriatic arthritis.

Screening leads to earlier diagnosis and treatment, which can slow the progression of the disease and reduce the joint damage that patients suffer. Indeed, a recent study of 283 psoriatic arthritis patients found that the 29% of patients who saw a rheumatologist within 6 months of their first symptom even responded better to treatment than other patients. Those who waited more than a year for treatment were significantly less likely than those who waited less than 6 months to achieve a complete drug-free remission. Delayed treatment was also associated with peripheral joint erosions (odds ratio [OR], 4.25; p=.001) and worse Health Assessment Questionnaire scores (OR, 2.2; p=0.004).

However, the results of the meta-analysis suggest that many of the dermatologists and primary care doctors who usually treat patients with psoriasis are not following guidelines and detecting arthritis as early as they should.

A major barrier to detection is the lack of any definitive diagnostic test. Physicians must learn to diagnose psoriatic arthritis on the basis of symptoms — including fatigue, stiff and swollen joints, eye pain, and changes in fingernails and toenails — and the systematic elimination of other diseases that cause similar problems. Another barrier to diagnosis is that older patients tend to chalk up many of these symptoms to the normal aging process and often fail to report them, even when asked by their doctors.