The paradigm of non-radiographic sacroiliitis—why the ongoing doubts?

Excerpt

The concept of non-radiographic axial spondyloarthritis (nr-axSpA) gained prominence from the understanding that definite plain radiographic features of sacroiliitis evolve over many years, and diagnosis is often delayed, while treatment is particularly effective in the early stages of disease. Many patients presenting with features suggestive of SpA but without radiographic sacroiliitis were indiscriminately labeled as “undifferentiated SpA” but then denied highly effective tumor necrosis factor inhibitor (TNFi) therapies because the drug label confined treatment to those with radiographic sacroiliitis. It became necessary to capture these patients with early disease in new classification criteria that would include patients within a broader spectrum of axSpA, which became possible with the advent of MRI for early detection of sacroiliitis. This was accomplished using a two-pronged approach in the 2009 Assessments in SpondyloArthritis international Society (ASAS) classification criteria [1]: (1) An imaging arm allows patients to be classified as having axSpA if they have MRI evidence of sacroiliitis and at least one SpA feature. (2) A clinical arm permits classification of axSpA in the absence of MRI inflammation if the patient is positive for HLA B27 and has at least two SpA features. A positive MRI for the purposes of classification was defined by a 2009 consensus of ASAS experts as bone marrow edema (BME) on fat-suppressed scans or osteitis on T1-weighted contrast-enhanced scans in a typical subchondral location [2]. This definition required the presence of at least two BME lesions on a single semicoronal slice through the SIJ or a single lesion on two consecutive slices. The lesion also had to be considered “highly suggestive” of axSpA although what characteristics of the lesion would define it as “highly suggestive” were not elaborated. A 2016 consensus update of the 2009 ASAS definition further elaborated that the concomitant presence of structural lesions, especially erosion, could help determine whether the BME lesion was “highly suggestive” of axSpA [3]. …