Features of Undifferentiated Spondyloarthropathy and Juvenile Spondyloarthropathy Among Asian Populations

The spondyloarthropathies (SpA) are defined as inflammatory arthropathies characterised by sacroiliac involvement and a relationship to HLA-B27. Undifferentiated spondyloarthropathy (USpA) includes the forms that do not meet the criteria for the established categories of SpA. The clinical spectrum of USpA is therefore wide, due to the various combinations of clinical and radiological manifestations of SpA. In a European population study, USpA was found to be the second most common clinical entity in the SpA group. However few studies have been published on USpA, since it has usually been overlooked due to inadequate classification criteria. Juvenile onset spondyloarthropathy (JSpA) is a term that refers to a group of HLA-B27-associated inflammatory disorders affecting children under the age of 16 years. Unlike adult SpA, there is higher prevalence of peripheral arthritis/enthesitis and lower axial symptoms. Although USpA is common, and juvenile ankylosing spondylitis (JAS) has different clinical features and a different prognosis from adult ankylosing spondylitis (AAS), few studies in Asia on these entities have been published. This paper reviews the literature on USpA and JSpA (particularly JAS) among Asian populations, and compares it to Western population studies.