The involvement of the spine in psoriatic arthritis

Although different classification criteria have been developed for psoriatic arthritis (PsA) and spondyloarthritis (SpA), a clear distinction is still not always possible in daily practice. In addition, clinical examination of patients initially diagnosed as PsA due to peripheral symptoms and skin lesions may also show inflammation in the axial skeleton causing inflammatory back pain, stiffness and changes on imaging including sacroiliitis, spondylitis and syndesmophyte formation, similar to what is known from ankylosing spondylitis (AS), the prototype of SpA. However, and in contrast to patients with AS, the long-term radiographic progression of patients with axial disease in PsA seems to be rather independent from spinal mobility. If axial symptoms predominate, diagnosis and classification can be made as axSpA - with or without psoriasis. Furthermore, also the role of HLA-B27 appears to be different in patients with PsA. Overall, the most data about axial involvement in SpA come from AS and axSpA studies, while data about the axial involvement in PsA is limited. Finally, there are no approved therapies for treatment of axial PsA at present, despite significant clinical morbidity. In recent years, anti-TNF therapies have revolutionised the management of ax-SpA. The new GRAPPA treatment recommendations have given specific management advice for patients with axial involvement based on literature from AS and axial SpA. This review aims to give an overview of the existing evidence, the clinical and imaging presentation, and therapeutic consequences of axial involvement in patients with PsA.