Age at onset in axial spondyloarthritis around the world: data from the Assessment in SpondyloArthritis international Society Peripheral Involvement in Spondyloarthritis study

OBJECTIVE: Age at onset is useful in identifying chronic back patients at an increased risk of axial SpA (axSpA). However, the majority of data on which the criterion of age at onset <45 years is based originates from Europe. Therefore it is unknown if this criterion applies in other parts of the world. We aimed to assess the age at onset of axSpA and its relationship with HLA-B27 and gender across the world. METHODS: Analyses were applied to patients from 24 countries across the world with an axSpA diagnosis and known age at onset of axial complaints. Cumulative probability plots were used to display the cumulative distribution of age at onset of axial symptoms. Linear regression models were built to assess the effect of HLA-B27 and gender on age at onset of axial symptoms. RESULTS: Of 2579 axSpA patients, 92% had an age at onset of axial symptoms <45 years, with only small variations across the geographical regions [Asia, n = 574 (94%); Europe and North America, n = 988 (92%); Latin America, n = 246 (89%); Middle East and North Africa, n = 771 (91%)]. Age at onset of axial symptoms was consistently lower in HLA-B27-positive patients {median 25 years [interquartile range (IQR) 19–32] vs 31 [IQR 22–39]} and male patients [median 25 years (IQR 19–33) vs 28 (IQR 21–37)], but in multivariable models an additional statistically significant effect of male gender independent of HLA-B27 was only found in Asia. CONCLUSION: Around the world, the great majority of axSpA patients had an age at onset of axial disease of <45 years, with HLA-B27 and male gender associated with earlier disease onset.