juvenile idiopathic arthritis. Subgroup characteristics and comparisons between rheumatoid arthritis-like subgroups and ankylosing spondylitis-like subgroups

In terms of adult-onset definitions. rheumatoid arthritis (RA) and ankylosing spondylitis (AS) are rarely diagnosed in children Adult RA is in most aspects similar to seropositive polyarticular arthritis in children, but AS differs in its clinical presentation according to age at onset. In general, the nomenclature and classificalions of arthritis in children encompass sub-groups with specific signs or laboratory tests and pathogenic mechanisms that distingiush one clinical form from the other. While one of these supgroups corresponds to RA, the one related to AS usually includes children with undifferentiated SpA and not definite AS. Puts, comparisons of RA and AS in children actually correspond to comparisons of various forms of childhood arthritis, currently classified as juvenile idiopathic arthritis (JIA) and AS in its early undifferentiated form. lit this paper. we review these to finally compare, the two populations.