Axial spondyloarthritis: thoughts about nomenclature and treatment targets.

The spondyloarthritides (SpA) are a heterogenous group of rheumatic diseases which are genetically linked. The strongest genetic factors, HLA B27, ERAP-1 and IL-23R, are found at variable rates in subgroups. The new nomenclature differentiates predominantly axial SpA (axSpA) from predominantly peripheral SpA (pSpA). Axial SpA (Ax-SpA) is further classified as classical ankylosing spondylitis (AS) and a non-radiographic form, nr-axSpA, which may occur in association with psoriasis (Pso) or chronic inflammatory bowel disease (IBD). Peripheral SpA includes patients with psoriatic arthritis (PsA) and IBD, patients who report a triggering infection (reactive arthritis), and other patients who may be classified simply as 'undifferentiated'. The most relevant target of therapy clinically is reduction of disease activity, which is associated with control toward ablation of inflammation, normalisation and/or improvement of function and mobility, prevention of osteoporotic fractures, and inhibition of structural changes (new bone formation) in the spine.