Syndesmophyte Development Linked to Combined Axial Involvement, Elevated CRP in PsA

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Syndesmophyte development was 4 times more probable when patients had a clinical or radiographic description of axial involvement combined with elevated C-reactive protein.

The probability of developing syndesmophytes in patients with psoriatic arthritis (PsA) is low, however, it is more likely when axial involvement is assessed radiographically, particularly when combined with elevated C-reactive protein (CRP), according to a study published in Annals of the Rheumatic Diseases.1

“Depending on the description, axial involvement is reported in 25%–70% of the patients with PsA,” wrote a team of investigators led by Manouk de Hooge, PhD, associated with the Molecular Immunology and Inflammation Unit, VIB-UGent Center for Inflammation Research and University Hospital Gent, Belgium. “The wide variability is a direct cause of the ongoing debate how to define axial involvement in PsA. With the lack of explicit definitions for axial involvement or criteria specifically for axial PsA (axPsA), the classification of axPsA is subject to many interpretations.”

Typical symptoms of axPsA include back pain which improves with exercise or worsens in rest, as well as morning stiffness lasting >30 minutes. Some researchers use radiographic damage as a strategy to quantify axial involvement in PsA, some evaluate the presence of spinal damage or syndesmophytes, and others describe the condition as unilateral or bilateral sacroiliitis.2

To understand the link between the different definitions of axial involvement and the chance of developing syndesmophytes over a 2-year period, investigators recruited patients with PsA from the Belgian Epidemiological Psoriatic Arthritis Study (BEPAS). The cohort consisted of patients from 17 Belgian rheumatology practices, with eligible participants meeting the classification criteria for PsA. Axial Involvement was determined using 6 clinical and 2 radiographic oriented definitions.

Patients received pelvic and spinal radiographs at baseline and year 2, which were interpreted by 2 calibrated central readers. Radiographic damage was evaluated using the modified Stroke Ankylosing Spondylitis Spinal Score and modified New York criteria. The development of new syndesmophytes at the 2-year mark were defined as conditional on axial involvement at baseline. The various definitions of axial involvement were assessed individually, and logistic regression analyses evaluated the link between axial involvement and the development of syndesmophytes.

Investigators obtained 2-year follow-up spinal radiograph data from 150 patients, of which 11 had new syndesmophytes at the end of the observation period. The mean age of patients was 54.3 years, mean disease duration was 8.8 years, and 41.3% of patients were female. According to a global assessment, 47.3% of patients fit the definition for axial involvement, which increased to 76.5% when using a less strict definition. Most (67.6%) patients reported chronic back pain.

The clinical definitions of axial involvement included back pain, inflammatory BP, a detailed assessment, and a global assessment. Using this criteria, the probabilities of developing syndesmophytes were similar for those with the presence or absence of the definition and ranged between .06 and .08. However, when including CRP to the definitions, the probability increased 2 times for patients with chronic back pain and 7 times for those with inflammatory back pain.

Similar results were observed with radiographic axial involvement, as the probability was 3 times higher when using the radiographic sacroiliitis definition. Additionally, when combined with elevated CRP, patients had a 14 times higher chance of developing syndesmophytes within 2 years. None of the odds ratios were statistically significant, and they ranged from .83 to 13.80.

“The overall scarce literature of follow-up studies on axial involvement in PsA patients combined with the increased discussion on defining axPsA calls for papers like this to gain insights and increase the understanding of PsA,” investigators concluded.


  1. de Hooge M, Ischenko A, Steinfeld S, et al. Specific descriptions of axial involvement are associated with radiographic damage development after 2 years in psoriatic arthritis patients [published online ahead of print, 2023 Nov 2]. Ann Rheum Dis. 2023;ard-2023-224501. doi:10.1136/ard-2023-224501
  2. Mease PJ, Palmer JB, Liu M, et al. Influence of axial involvement on clinical characteristics of Psoriatic arthritis: analysis from the Corrona Psoriatic arthritis/Spondyloarthritis Registry. J Rheumatol 2018;45:1389–96. doi:10.3899/jrheum.171094