Abstract and Introduction
Purpose of review: Of the four musculoskeletal domains of psoriatic arthritis (PsA), the axial domain is the least studied. With the advent of targeted therapy that is efficacious in some but not all manifestations of spondyloarthritis (SpA), there is interest in understanding the similarities and differences between axial PsA (axPsA) and ankylosing spondylitis. Moreover, there is also interest in evaluating the axial domain in PsA clinical trials, domain that has traditionally been ignored in such studies. This review aims to summarize the current understanding of the differences between ankylosing spondylitis and axPsA.
Recent findings: Recent observational studies have shown that axPsA forms part of the SpA spectrum, flanked by peripheral PsA on one side and ankylosing spondylitis on the other. Thus, axial disease is more severe in ankylosing spondylitis, whereas peripheral disease is more severe in axPsA. However, the overall disease burden and impact is similar. The expression of axPsA is influenced by age, disease duration, sex and HLA-B*27 status.
Summary: axPsA has not been properly defined hampering research into pathogenesis, disease impact and treatment. Research to define prevalence, clinical features, impact, similarities and differences with other axial SpA, and treatment is an unmet need.
Psoriatic arthritis (PsA) was defined as psoriasis associated with inflammatory arthritis (peripheral arthritis and/or spondylitis) and usually a negative serologic test for rheumatoid factor by Moll and Wright. In addition, they described five clinical patterns of PsA, spondylitis/axial arthritis being one. Ankylosing spondylitis is an inflammatory arthritis that predominantly affects the axial joints and is often associated with extra-articular manifestations including psoriasis. Both diseases belong to a spectrum of diseases termed spondyloarthritis (SpA) that is characterized by peripheral as well as axial arthritis, radiological sacroiliitis, mucosal and skin inflammation, tendency for familial aggregation, absence of rheumatoid factors and absence of subcutaneous nodules. As patients diagnosed with PsA may have axial arthritis and those with ankylosing spondylitis may have psoriasis, the question arises that if the two conditions – axial PsA (axPsA) and ankylosing spondylitis with psoriasis – are the same or different. This question has been sporadically investigated in the past. With the advent of targeted therapy that is efficacious in some but not all manifestations of SpA (e.g. IL-23 inhibitors) there is renewed interest in understanding the similarities and differences between axial PsA and ankylosing spondylitis. Moreover, there is also interest in evaluating the axial domain in PsA clinical trials, domain that has traditionally been ignored in such studies. This review aims to review studies comparing axial PsA and ankylosing spondylitis and suggest future research.
Curr Opin Rheumatol. 2019;31(4):329-334. © 2019 Lippincott Williams & Wilkins