Juvenile onset ankylosing spondylitis (JAS) has less severe spinal disease course than adult onset ankylosing spondylitis (AAS): clinical comparison between JAS and AAS in Korea

OBJECTIVE: To assess the frequency of juvenile onset ankylosing spondylitis (JAS) in Korean patients with AS and to differentiate the clinical characteristics of JAS from adult onset ankylosing spondylitis (AAS). METHODS: We studied 98 consecutive patients with AS who visited the rheumatology clinic of a tertiary referral center and compared clinical and radiographic features of JAS (n = 41) with those of AAS (n = 57). RESULTS: Median age at onset in JAS was 14 years (range 7-16) and in AAS 22 years (range 17-38) (p < 0.01). Patients with JAS at presentation showed fewer spinal symptoms and more frequent peripheral joint symptoms than those with AAS (41.5% vs 80.7% and 73.2% vs 36.8%, respectively; p < 0.01). Current cervical spine disease was more frequent in AAS (66.7% vs 43.9%; p = 0.02) and current knee disease in JAS (26.8% vs 8.8%; p = 0.02). Patients with JAS showed a shorter tragus-wall distance (mean +/- SD 10.6 +/- 1.7 vs 13.1 +/- 6.9 cm; p < 0.01), more mobility on the modified Schober test (5.7 +/- 2.0 vs 4.0 +/- 2.6 cm; p < 0.01) and chest expansion (4.4 +/- 1.7 vs 3.2 +/- 1.8 cm; p < 0.01), and a better forced vital capacity (75.1 +/- 14.1% vs 82.1 +/- 16.1% of predicted value; p = 0.03) than those with AAS. Totally ankylosed sacroiliitis and spinal syndesmophyte on radiographs were less frequent in JAS patients than in AAS (19.5% vs 47.4% and 17.1% vs 54.4%, respectively; p < 0.01). CONCLUSION: The frequency of JAS (41.3%) among Koreans was higher than that reported for Caucasians. General joint involvement pattern at disease onset in JAS was similar to previous reports. Our data suggest that clinically and radiographically JAS has a less severe spinal disease course than AAS.