Facet Joint Involvement in Early MRI Positive Axial Spondyloarthritis

Abstract Background The disease course of non-radiographic axial spondyloarthritis (nr-axSpA), usually detected by magnetic resonance imaging (MRI), is often unclear at the time of diagnosis. We investigated which MRI findings in the sacroiliac joints (SIJs) and lumbar spine including the facet joints can be observed over a two-year period in patients with newly diagnosed active inflammatory lesions in the SIJs fufilling the Assessment of SpondyloArthritis International Society criteria (ASAS) for Axial Spondyloarthritis (axSpA). Methods Patients (n=56, age<45 years, 30 female and 26 male, symptom duration 3–30 months) consecutively diagnosed with unilateral or bilateral sacroiliitis through MRI during an 18-month period and meeting the ASAS criteria for axial SpA were followed up for two years. Clinical examination, laboratory tests and an MRI of the sacroiliac joints (SIJs), lumbar spine and facet joints were performed at diagnosis (t0), after one year (t1) and after two years (t2). Results At t0, 31 patients (55%) with a bone marrow edema (BME) in the SIJs already had detectable changes in the facet joints, including signs of inflammation or degenerative changes. At t2, patients with facet joint involvement in t0 not only had more significant changes in the SIJs but also significantly more changes in the vertebral bodies, including BME, fat lesions and vertebral body erosions than patients without changes in the facet joints at t0. All vertebral changes described might be potential indicators of progression to radiographic axSpA (r-axSpA). These MRI findings are seen more frequently over a short period of time than previously thought. Conclusions MRI progression in the SIJs over a two-year period is associated with increasing damage to the facet joints and vertebral bodies. Involvement of the facet joints in the early stages of the disease may indicate increasing changes in the vertebral bodies and thus a less favourable course of axSpA.