Nonradiographic axial spondyloarthritis background and confounding factors of this new terminology: an appraisal.

The advent of biologic therapy in the treatment of rheumatic diseases has intensified the need to further define and characterize spondyloarthritis (SpA). There has been a long debate over nomenclature of the SpA subtypes. There are those who are considered "lumpers," favoring the notion that different entities of the SpA groups are manifestations of the same disease, and "splitters," those who believe the different SpA groups represent separate diseases with shared clinical features. The influential work by Moll et al. has led to separation of entities and recognition of etiological processes of SpA subtypes. Among these subtypes has emerged nonradiographic axial spondyloarthritis (nr-axSpA), which is believed to be either an early form of ankylosing spondylitis (AS) or perhaps a different disease entity altogether. Recently attention has shifted to the characterization of early SpA, with special emphasis on nonradiographic axial SpA. The Assessment of Spondyloarthritis International Society (ASAS) has developed new criteria for the classification of this disease entity. Along with the advent of these criteria have come several unanswered questions. Although data suggests that nr-axSpA will evolve into AS over time, the natural evolution of disease is still undetermined since a proportion of cases do not progress. A number of questions also remain regarding features of patients with AS compared to those with nonradiographic disease. This appraisal highlights the differences in disease characteristics between men and women in regards to measures of disease activity, inflammatory markers, and radiologic findings. Recent studies also suggest fibromyalgia as a potential confounding factor in assessing disease activity and establishing a diagnosis of axSpA in the female population. Nonradiographic axial SpA is a relevant disease subgroup of axial SpA, and several questions have been left unanswered with more research needed regarding diagnosis (particularly in women), treatment, and long-term disease course.