Enthesitis-Related Juvenile Idiopathic Arthritis

Juvenile idiopathic arthritis (JIA) is defined as arthritis in children before their 16th birthday lasting for at least 6 weeks in the absence of another cause. The nomenclature surrounding chronic arthritis of childhood was revisited in the mid-1990s by the International League of Associations for Rheumatology, at which time the umbrella term juvenile rheumatoid arthritis was changed to juvenile idiopathic arthritis. In 2004, the International League of Associations for Rheumatology revised the previously defined 7 categories of JIA (Table 1), each with complex inclusion and exclusion criteria. Enthesitis-related JIA, or ERA, is the subcategory of JIA that can evolve into the adult form of ankylosing spondylitis; however, the differences in categorization between juvenile and adult forms of chronic arthritis are not clear-cut, and patients may be recategorized after their 16th birthday.

ERA affects approximately 10% to 20% of children with JIA. Hallmarks of disease include arthritis, defined as nonbony swelling or tenderness/pain on motion with limitation of motion, and enthesitis, defined as tenderness where the tendon or ligament inserts onto bone. Patients who have either arthritis or enthesitis, but not both, can also fall under the category of ERA if they have 2 of the other associated criteria (Table 2). Unlike many other autoimmune diseases, ERA has a male predominance (60%). The average age at diagnosis is 12 years, and most patients are either HLA-B27 …