Purpose of review: The concept of axial spondyloarthritis with two forms or subtypes (nonradiographic and radiographic) has been established over the last few years. However, debates concerning especially the nonradiographic form of the disease are still ongoing. Here we summarise recent data on similarities and differences (and their possible explanations) between nonradiographic axial spondyloarthritis and radiographic axial spondyloarthritis (ankylosing spondylitis).
Recent findings: Nonradiographic and radiographic forms are about equally frequent among patients first diagnosed with axial spondyloarthritis and have in general similar clinical characteristics, especially related to clinical signs of disease activity and similar rates of treatment response. Nonradiographic axial spondyloarthritis is characterised by a higher prevalence of females and lower percentage of patients with elevated C-reactive protein that might reflect the presence of a certain proportion of patients who develop structural damage in the axial skeleton very slowly or do not develop it at all. Elevated C-reactive protein and active sacroiliitis on magnetic resonance imaging are strongest predictors of structural damage development in the sacroiliac joints and, therefore, of progression from nonradiographic to radiographic stage. The same parameters predict a good clinical response to therapy with tumour necrosis factor alpha blocking agent in axial spondyloarthritis, but especially if used in nonradiographic disease.
Summary: Currently available data support the concept of axial spondyloarthritis as one entity. Nonradiographic axial spondyloarthritis seems to be, however, more heterogeneous than ankylosing spondylitis because of the presence of patients with a self-limiting disease or a slow disease course.