How is early spondyloarthritis defined in the literature? Results from a systematic review

Aim: To identify all possible definitions of "early SpA" employed in the literature, including "early axial SpA (axSpA)" and "early peripheral SpA (pSpA)". Methods: A systematic literature review was conducted in Medline, EMBASE and the Cochrane Library for studies that included any mention of "early SpA" or its subtypes. The proportion of studies including a definition was calculated, and the different definitions were assessed. Results: Out of 9651 titles identified, 336 publications reporting data from 183 studies were included. Over time, an increasing number of publications were identified. In total, 114 (62%) studies reported a specific definition: 33% of them based it on symptom duration, 31% on radiographic damage, 28% on disease duration, 5% on both symptom/disease duration and radiographic damage, and 3% on other aspects. Overall, 61 (33%) studies included the term "early axSpA", whereas 60 (33%) included "early ankylosing spondylitis (AS)". Regarding the studies that referred to "early axSpA", the most used definition was symptom/disease duration <5 years, whereas for "early AS" was symptom/disease duration <10 years. After 2010, the definition of "early axSpA" based on the absence of radiographic sacroiliitis was less used compared to before 2010 (17% vs 38%). Conclusion: Over time, the term "early SpA" and its subtypes is increasingly used. More than one third of the studies did not include a definition of the term and the studies reporting one showed a large heterogeneity. These results emphasize the need for a standardised definition of early SpA.