Objectives: An important unresolved issue in pathogenesis and clinical course of ankylosing spondylitis (AS) has been whether juvenile-onset AS (JoAS) is a clinical entity in its own right, or just an earlier onset variant of its adult-onset AS (AoAS) counterpart. In this study, we address this issue.
Methods: All AS patients were extracted from the database of a large Spondylitis Clinic. Those with symptom onset of ≤ 16 years were compared to those with symptom onset ≥ 17 years. Odds ratios (OR) were calculated and adjusted for disease duration and current age.
Results: 267 AS patients were identified. 84 met criteria for JoAS and 183 met criteria for AoAS. There were no differences in gender ratio (Males: JoAS 81%; AoAS: 79%), nor in HLA-B27 status (positive: JoAS 75%; AoAS 81%). The axial/peripheral pattern of disease at presentation differed: an exclusively peripheral pattern was seen in 26% JoAS but in only 4.6% AoAS (p<0.0001). There were no differences in disease activity between the two groups. Adjusted for disease duration, axial features were more prominent in AoAS than JoAS as represented by neck pain [OR 2.93 (1.54,5.55)], neck stiffness [OR 3.39 (1.80,6.39)], back pain [OR 2.96 (1.43,6.11)], back stiffness [OR 3.30 (1.50,7.28)]. Adjusted for disease duration, AoAS was associated with worse functional and quality of life measures, and higher fatigue scores.
Conclusions: JoAS follows a distinctive clinical course from its AoAS counterpart. Furthermore, these clinical features are dictated by factors other than male gender and HLA-B27 and warrant further investigation.