Background/Purpose: Ankylosing spondylitis (AS) is a chronic inflammatory disease that mainly affects the axial skeleton in which the diagnosis includes diagnostic X-ray changes in the sacroiliac joints. The spectrum of axial spondyloarthritis (axSpA) ranges from non-radiographic (nr) axSpA to AS. Variable rates of progression from nrAxSpA to AS have been reported. However, factors predictive of this progression are poorly defined. In this study, we aimed to identify the characteristics of patients who progressed from nrAxSpA to AS according to modified New York criteria (mNYc). 

Methods: In our registry, there were 44 nraxSpA patients according to the ASAS definition who had serial follow-up pelvic X-rays. Two independent readers scored the first and last available pelvic radiographs for each patient and identified the patients who progressed to AS. Discordant results were settled by a third reader. Spinal radiographic damage was assessed by the modified Stoke AS Spinal Score (mSASSS). Baseline information regarding symptom duration, B27 status, biological drug usage, clinical variables, smoking, BASDAI, ESR and CRP were then obtained from the database.

Results:

Characteristics of progressors:  Over a median period of 52.5 (25-126) months, 9 (20.5%) out of 44 patients progressed from non-radiographic stage to AS at a rate of  4.7%/year.The median transition time was 47 (23-89) months. There were 8 (88.9%) men and 1 (11.1%)woman. The median age at diagnosis was 22.3 (18-63) years. The median disease duration was 5 (1-19) years. HLA-B27 was positive in 7 (77.8%) patients. Smoking history was positive in 5 (55.6%) patients. The frequency of arthritis, uveitis, enthesitis, dactylitis and family history of AS were 6 (66.7%), 3 (33.3%), 5 (55.6%), 1 (11.1%) and 2 (22.2%) respectively. There were 6 (66.7%) patients who had been treated with TNF-inhibitors (TNFi). Comparison of progressors vs. non-progressors: There were 35 patients who did not progress to AS. The median follow-up of these patients were 33 (24-89) months. Comparison of both groups showed that follow-up duration, disease duration, HLA-B27 status, smoking, extra-articular features, family history, baseline BASDAI, and TNFi treatment were not different between the groups. On the other hand, progressors showed significantly higher baseline CRP, higher frequency of male sex and lower age at onset compared to the non-progressors (Table-1). 

Conclusion: Male sex, younger age at onset and higher baseline CRP are factors predictive of progression from nr-axSpA to AS. 

Table 1: Comparison of baseline profiles of nr-axSpA progressors vs non-progressors.

* Data is presented with median (minimum-maximum) values

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/clinical-characteristics-of-axial-spondyloarthritis-patients-progressing-from-non-diagnostic-to-diagnostic-radiographic-sacroiliitis/