Boundaries between familial Mediterranean fever and juvenile spondyloarthritis: Analysis of three French retrospective cohorts.

Children with Familial Mediterranean fever may suffer from musculoskeletal involvement, somewhat difficult to distinguish from juvenile spondyloarthritis. The association of these two diseases has been scarcely reported in children. Objective of this work was to define the association of familial Mediterranean fever and juvenile spondyloarthritis in France. Three cohorts of children with familial Mediterranean fever, juvenile spondyloarthritis, familial Mediterranean fever related juvenile spondyloarthritis, were retrospectively identified in the French reference center of auto-inflammatory diseases. Familial Mediterranean fever was defined according to Tel-Hashomer or Turkish pediatric criteria with at least one exon-10 MEFV-gene mutation. Juvenile spondyloarthritis was defined according to ILAR criteria. Patients with familial Mediterranean fever or juvenile spondyloarthritis were respectively compared to familial Mediterranean fever related juvenile spondyloarthritis patients. Sixteen children were identified as having familial Mediterranean fever related juvenile spondyloarthritis. The male/female-ratio was 0.6, with median age at spondyloarthritis onset of 7.5years (3-16years). All carried at least one M694V variant in MEFV gene; 16.7% were HLA-B27-carriers. Compared to 83 familial Mediterranean fever patients, familial Mediterranean fever related juvenile spondyloarthritis patients had less frequently fever (P<0.01) and more frequently arthritis (P<0.05), enthesitis (P<0.001), inflammatory back pain (P<0.001), inadequate response to colchicine (P<0.05). Compared to 20 juvenile spondyloarthritis patients, familial Mediterranean fever related juvenile spondyloarthritis patients less often received non-steroidal anti-inflammatory drugs (P<0.01) and anti-tumor necrosis factor drugs (P<0.001). Familial Mediterranean fever may be associated with typical pattern of juvenile spondyloarthritis. These patients, with less response to colchicine, should be diagnosed earlier and treated as for jSpA