Juvenile ankylosing spondylitis (JAS) is a chronic inflammatory disorder belonging to the group of juvenile-onset spondyloarthritides. It occurs prior to the age of 16 years and primarily leads to enthesopathy, spinal abnormalities, and peripheral joint inflammation.
Ankylosing spondylitis (AS) is a chronic inflammatory rheumatic disease that causes pathologic changes both axially and in the regions of ligament and tendon attachments to the skeleton . Juvenile ankylosing spondylitis (JAS) affects children and adolescents younger than 16 years of age and presents considerably differently than adult-onset AS. One of the first mentions of JAS in the scientific literature was by Moll and Wright in 1976 which described a pediatric disease that mainly leads to an inflammation of the entheses and peripheral joints, possibly progressing to axial involvement  .
The initial manifestations with which JAS patients present are that of monoarthritis or oligoarthritis that usually involves peripheral enthesitis, tarsal disease, and, relatively rarely, sacroiliitis and spinal inflammation . The predominance of lower extremity involvement is irrefutable in JAS and arthritis tends to be asymmetric. Disease progression is also fluctuant. Some patients may experience one occurrence of asymmetric arthritis that responds to treatment and does not recur, whereas others may face a progressive disease that will eventually cause serious sequelae to the affected structures . Even though it is a rare clinical manifestation diagnosed in approximately 1/5 of JAS patients, acute anterior uveitis may coexist and so may additional extra-articular manifestations, including conduction heart disease, valvular disease, and lung disease   . Spinal involvement usually appears years after the early symptoms have been observed, mostly after an average period of 6 to 8 years . Nonspecific complaints which may also be reported by the young patients include a kyphotic appearance due to progressed disease that has affected the spine, weight loss, decreased appetite, fatigue, and dyspnea.
Diagnosis of both juvenile and adult ankylosing spondylitis, similarly to other spondyloarthritides, is frequently delayed, with up to 10 years passing from the occurrence of the initial symptoms to the definitive diagnosis . JAS is often underdiagnosed or misdiagnosed, and the wider medical community displays a lack of adequate level of information regarding such rheumatic conditions.
The 1984 Modified New York Criteria for the diagnosis of AS are used to diagnose JAS as well and include:
The diagnosis of JAS is made when at least one clinical manifestation and at least one radiologic parameter are present.
Sacroiliitis is usually diagnosed radiographically. The disadvantage of this imaging modality is that sacroiliac joint involvement will be depicted on an X-ray late in the course of the disease. Due to this reason, magnetic resonance imaging (MRI) scans has been gaining ground in the depiction of sacroiliitis in pediatric patients with suspected JAS. According to a study by Bollow et al., an MRI scan is considerably more sensitive to diagnose sacroiliac involvement in JAS patients than a plain radiograph .