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TORONTO — About 45% of patients with psoriatic arthritis (PsA) showed sacroiliitis progression over time, and nearly 23% developed definitive radiographic sacroiliitis, one of the largest longitudinal real-world cohort studies had found.

“Radiographic sacroiliitis progression in psoriatic arthritis is relatively common, particularly in patients with higher inflammatory burden,” study author Virginia Carrizo Abarza, MD, told Medscape Medical News.

The study also showed less progression after the year 2000, when exposure to biologic and targeted synthetic disease-modifying antirheumatic drugs (DMARDs) increased.

Carrizo Abarza presented the findings during the Spondyloarthritis Research and Treatment Network (SPARTAN) 2026 Annual Meeting.

There’s quite a lot of data on axial involvement among patients with axial spondyloarthritis (axSpA), but “there’s a gap in the literature” when it comes to PsA, said Carrizo Abarza, who at the time of the study was a fellow at the Gladman Krembil Psoriatic Arthritis Program at the University of Toronto, Toronto, Ontario, Canada. She is currently working as a data review manager at IQVIA.

“Most previous studies combined axial SpA and PsA populations, making it difficult to understand the specific behavior of axial PsA,” she said. “ As we don’t have a lot of data on patients with psoriatic arthritis, we don’t know the features of the axial involvement in this kind of patient.”

The study included 1554 patients with PsA who were recruited from 1978 to 2025 at one academic medical center clinic. The median follow-up time was 6 years, with evaluations every 6-12 months.

Investigators collected pelvic x-rays biannually and read these according to the modified New York (mNY) criteria. Radiograph findings were determined by the consensus of at least two rheumatologists.

Sacroiliitis Sum Score (SSS) Outcome

The main outcome used the SSS, which ranges from 0 to 8 and is calculated as a total sacroiliitis grade for the left and right sacroiliac joints using the mNY grading scale (0-4 per joint). Progression was defined as an increase in the SSS by ≥ 1 point.

“Use of the Sacroiliitis Sum Score allowed us to detect subtle radiographic changes over time,” Carrizo Abarza commented.

The study found about 45% of patients (475 of 1056) showed progression.

Certain disease characteristics and activity scores were associated with greater radiographic sacroiliitis progression, including nail disease (estimate, 0.061; 95% CI, 0.010-0.113) and Psoriasis Area and Severity Index (PASI) score (0.008; 95% CI, 0.004-0.013). HLA alleles were not significantly associated with progression.

Progression to Definite Radiographic Sacroiliitis

A secondary outcome used a different approach to capture progression by instead monitoring the development of definitive radiographic sacroiliitis over time. C onversion to definite mNY sacroiliitis was defined as bilateral grade ≥ 2 sacroiliitis or unilateral grade ≥ 3 sacroiliitis.

The study found 22.7% of patients (189 of 831) developed definite radiographic sacroiliitis by mNY criteria.

Related associated factors included nail disease (hazard ratio [HR], 1.40; 95% CI, 1.05-1.88 in univariable analysis) and PASI score (HR, 1.05; 95% CI, 1.03-1.06 in univariable analysis).

The models suggested DMARD exposure had a protective effect. This seems to align with an analysis by calendar year that found that after the year 2000, patients had lower odds of progression.

“We can see that in earlier decades, patients progress more rapidly compared with patients in recent decades, particularly after 2011,” said Carrizo Abarza, referring to a graph illustrating the probability of remaining free of progression over time.

In addition to the introduction of biologic treatments and wider access to these medications, slowing of progression might be explained by a trend to earlier diagnosis, she said.

Biologic or targeted synthetic DMARDs (HR, 0.53; 95% CI, 0.31-0.89) and diagnoses during 2000-2010 (HR, 0.51; 95% CI, 0.36-0.74) as well as during 2011-2025 (HR, 0.26; 95% CI, 0.14-0.46) showed a protective effect.

Notably, many of the factors associated with progression in the univariable models were not significant in the multivariable models.

“These new findings reinforce the concept that persistent inflammation across different disease domains may contribute to structural damage, while modern treatment strategies and advanced therapies may help reduce progression,” Carrizo Abarza said.

The results are limited by the observational, single-center design of the study and its lack of systematic MRI data, which prevented researchers from assessing the impact of inflammation on structural progression.

MRI Scoring Would Represent an Advance

The study results aren’t unexpected, said Walter P. Maksymowych, MD, professor in the Department of Medicine (Rheumatology) at the University of Alberta, Edmonton, Alberta, Canada, in comments to Medscape Medical News.

He noted the finding that almost 23% of patients with PsA develop radiographic sacroiliitis “is consistent with recent data” from the multicenter AXIS study, which enrolled 409 patients with PsA, reported that axial involvement was present in 27.4% of patients.

The newly presented results aren’t likely to significantly change clinical practice, at least until better imaging modalities become more widely available, Maksymowych said. “Radiographic evaluation of the sacroiliac joints is unreliable and is only used because much better imaging modalities, especially MRI, are expensive and not readily accessible.”

He noted that a better way to capture structural damage progression in the sacroiliac joints is to use an MRI scoring platform developed in Canada, the Spondyloarthritis Research Consortium of Canada MRI Sacroiliac Joint Structural Score.

Carrizo Abarza and Maksymowych had no relevant conflicts of interest.