USE OF DYNAMIC MAGNETIC-RESONANCE-IMAGING TO DETECT SACROILIITIS IN HLA-B27 POSITIVE AND NEGATIVE CHILDREN WITH JUVENILE ARTHRITIDES

Objective. Involvement of the sacroiliac (SI) joints is a hallmark of the spondyloarthropathies (SpA), especially, in early and later stages of ankylosing spondylitis in adults. The significance of sacroiliitis in juvenile SpA is less clear and the diagnosis of juvenile SpA is di fficult due to the mostly nonspecific or absent history of back pain i n children and the time delay associated with the diagnosis of sacroil iitis by conventional radiographs. Our aim was to evaluate dynamic mag netic resonance imaging (MRI) of the SI joints in children and to asse ss the frequency and the determinants of SI joint involvement in juven ile SpA and other juvenile arthritides. Methods. Clinical examinations and dynamic MRI were performed in 130 children < 16 years of age with joint complaints, 100 with probable SpA, and 30 controls. The degree of back pain was assessed by a visual analog scale (VAS) (0 = no pain, 10 = very severe pain). The following groups were defined before MRI investigation according to modified European Spondylarthropathy Study Group (ESSG) criteria for SpA: Group 1: undifferentiated SpA (uSpA, n = 41, 88% B37+); Group 2: differentiated SpA (n = 29, 97% B27+, compri sing reactive arthritis (n = 16), ankylosing spondylitis (n = 9), psor iatic arthritis (n = 3), and arthritis in inflammatory bowel disease ( n = 1); Group 3: patients with no signs of SpA other than oligoarthrit is, here named juvenile chronic arthritis (JCA) II (n = 30, 93% B27+): Group 4: HLA-B27+ controls without arthritis (n = 12); and Group 5: H LA-B27-controls with various other non-SpA diagnoses (n = 18). MRI was evaluated according to published criteria allowing for differentiatio n between acute and chronic changes in SI joints. Results. Acute sacro iliitis without chronic changes could only be detected by dynamic MRI: in 17 patients (11 in Group 1, 3 in Group 2, 3 in Group 3) together i n 14/70 (20%) patients with SpA. All these 17 patients had normal pelv ic radiographs. Using MRI acute and/or chronic sacroiliitis were found in 35 patients: 17/41 in Group 1 (41%), 15/29 in Group 2 (52%), and 3 /30 (10%) patients in Group 3, but in no patients in Groups 4 and 5. C hronic SI joint changes > grade 1 were detected by MRI in 18/70 patien ts with SpA (25.7%). In comparison, radiographic changes > grade 1 wer e less often detected in 14/70 patients with SpA (20%) or 23/210 SI jo ints examined (11%), compared to 29/210 SI joints found in the MRI exa minations (14%) (p = 0.05). Among the 70 patients with SpA, those with MRI diagnosis of acute sacroiliitis had a significantly longer diseas e duration (62 +/- 34 vs 28 +/- 16 months; p = 0.01) and higher C-reac tive protein (12 +/- 12 vs 9 +/- 14; p = 0.01), and also reported more back pain on VAS (4.3 +/- 3.6 vs 1.2 +/- 2.2; p = 0.001) than these w ithout sacroiliitis. Conclusion. Dynamic MRI and MRI are useful to det ect acute and chronic sacroiliitis in children. The main advantages in comparison with conventional radiographs are the ability to detect ac ute changes in the SI joints, the higher sensitivity to detect chronic changes, and clearly, the lack of radiation exposure; while the disad vantages are the high costs and the duration of the procedure. Sacroil iitis is fairly common in juvenile SpA and seems to be associated with disease intensity and duration.