The age of psoriasis onset determines whether arthritis or psoriasis starts first in patients with psoriatic arthritis, according to new data presented at the American College of Rheumatology meeting. 

According to Umut Kalyoncu, MD, professor of internal medicine and rheumatology, at Hacettepe University in Turkey, and colleagues, the interrelationships between characteristics of skin psoriasis, arthritis and the timing of arthritis are not well studied. 

Man with psoriasis. Source: Getty

To explore this relationship in a large international cohort, Kalyoncu and colleagues studied data from 1631 patients in the PsART-international web-based registry of PsA patients under routine care in Turkey, Italy and Canada. 

"The PsART-International cohort focuses on PsA patients in whom musculoskeletal symptoms start before skin lesions, which is approximately five to 10 percent of all PsA patients. We need more patients to determine related factors," Kalyoncu wrote in a press release. "PsA is a heterogeneous disease for clinical presentation and treatment response. If patients with arthritis first are really a different subgroup, it means that treatment response and prognosis could be different from others. Indeed, in our cohort, achieving minimal disease activity is statistically less frequent in patients with arthritis first."

Data was extracted on demographic characteristics, family history or psoriatic disease, types of skin psoriasis, site of skin psoriasis onset, and components of psoriatic arthritis ever observed.

According to the abstract, there were three patient cohorts, arthritis-first (N = 71), psoriasis-first (N = 1251) and synchronous (N = 309). The synchronous group indicated the onset of skin and joint disease within 12 months. 

The primary outcome of the study was the absolute time elapsed in months after skin disease to arthritis.

A linear regression model for the primary outcome was constructed using demographic, skin disease and arthritis character to explore the associations.

The study showed that the age of psoriasis onset, not arthritis determined whether arthritis or psoriasis would be the first to appear. 

The regression analysis showed that the model intercept, delay of arthritis after psoriasis when other independent variables are set to their baseline values, is 65 months, pustular psoriasis is linked to onset of arthritis 2 years earlier than the intercept interval, however, nail involvement, plaque psoriasis or family history of psoriasis are linked to an increased delay from psoriasis to arthritis by 2 years. 

There was no material change in the point estimates when adding types of articular involvement into the model, however, there was reduced precision of terms for skin psoriasis type. 

"In our study, arthritis first is highly related with late-onset psoriasis. This means arthritis-first patients may be a different subgroup of PsA, and treatment response could be worse in these patients as well,” Kalyoncu wrote. “If these results are confirmed in other, well-defined PsA cohorts, we may have determined a subgroup of this highly heterogeneous disease."