Differences Between Axial PsA and axSpA May Warrant Classification As Distinct Disorders

Patients with axial spondyloarthritis (axSpA) and psoriatic arthritis with axial involvement (axial PsA) present with comparable disease burdens, though significant differences exist among clinical, genetic, and demographic characteristics, according to study findings published in Rheumatic & Musculoskeletal Diseases Open.

Investigators compared clinical and demographic characteristics of patients with axSpA (with or without psoriasis) vs those with axial PsA.

A cross-sectional comparison was conducted using data from the Swiss Clinical Quality Management (SCQM) registry from January 2006 through February 2023. Patients diagnosed with axSpA and PsA were included in the analysis, while those with missing data on the presence of axial involvement or psoriasis were excluded. Axial involvement in PsA was determined by the patient’s treating rheumatologist. 

5208 patients with axSpA and 2771 with PsA were included in the analysis.

Among the patients with axSpA, 479 (10.7%) had current or previous psoriasis, while 1153 (43.8%) patients with PsA presented with axial involvement.

At the time of inclusion in SCQM and at symptom onset, patients with axial PsA vs those with axSpA and psoriasis were of more advanced age, more frequently women, reported less back pain, had a higher prevalence of peripheral arthritis and severe swelling in fingers and toes, and were less likely to test positive for human leukocyte antigen B27 (HLA-B27).

Additionally, patients with axial PsA had shorter symptom duration and diagnostic delay.

Higher body mass index and greater prevalence of obesity were associated with patients with axSpA and psoriasis.

Patients with axial PsA vs axSpA and psoriasis had comparable function, mobility, and disease activity.

Patients with axial PsA more frequently had a family history of psoriasis or PsA, while patients with axSpA and psoriasis more frequently had a family history of axSpA.

Patients with axSpA and psoriasis were of more advanced age and reported longer symptom duration, though, onset of symptoms was more delayed, vs patients with axSpA without psoriasis.

Further comparison of patients with axSpA with vs without psoriasis revealed decreased prevalence of HLA-B27 positivity, more frequent peripheral musculoskeletal manifestations, decreased spinal mobility and function, increased disease activity, and comparable axial involvement.

Study limitations included the lack of a validated definition of axial PsA. Additionally, data on disease activity and severity of axial involvement were missing for most patients in the PsA cohort. Finally, data on patient imaging were not collected.

“The findings suggest that axSpA and axial PsA might be distinct entities,” the study authors concluded.

“Treatment studies specifically dedicated to axial PsA need to be conducted as soon as a consensus is found on the definition of axial involvement in PsA,” they noted.

Disclosure: This research was supported by Eli Lilly. One or more study authors declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of authors’ disclosures.