Low frequency of axial involvement in southern Italian Caucasian children with HLA-B27 positive juvenile onset undifferentiated spondyloarthritis

To establish how many children with HLA B27-positive juvenile undifferentiated spondyloarthritis (JuSpA) living in southern Italy develop axial disease after 5 years of disease. All children with B27-positive enthesitis-related arthritis (ERA) consecutively seen in a 7-year period were entered in a special register and were followed prospectively. Each patient was examined at 6-month intervals, even if asymptomatic. In patients with inflammatory spinal pain and/or buttock pain, MRI of the sacroiliac joints and spine was performed. Five years after inclusion, sacroiliac joint plain radiographs were obtained and read blindly after being mixed with those of control subjects. Thirteen children, 9 boys and 4 girls, with B27-positive ERA and one girl with B27-positive isolated SpA dactylitis were seen in the study period. Their median age at disease onset and at our first examination were 10 (range 2-16) and 12 years (range 3-16), respectively. During follow-up, only one patient had axial symptoms, i.e. alternate buttock pain. MRI revealed moderate bone oedema at both sacroiliac joints. After five years of disease, no patient showed reduced spinal movement. No sign of sacroiliitis was seen in any patient and control on plain films. A new MRI of the sacroiliac joints of the patient who showed bone oedema in the first years of disease was normal. This study confirms that the onset of axial involvement in Italian Caucasian HLA-B27 positive children with ERA is rare in the first five years of disease.