The word spondyloarthropathy (referring to arthritis of the spine and sacroiliac joints) evolved in the adult population to distinguish a group of chronic arthritides that differ from rheumatoid arthritis. These conditions are distinct in that they involve axial joints, are associated with the HLA-B27 haplotype, have a frequent family history of these diseases, and are rheumatoid factor-negative. Traditionally, the specifically named spondyloarthropathies included ankylosing spondylitis, psoriatic arthritis, the arthropathy of inflammatory bowel disease (IBD), and reactive arthritis (previously referred to as Reiter disease).
This characterization has not been entirely satisfactory because many patients do not comfortably fit into 1 of these explicitly defined categories. The efficacy of current pharmacotherapy for ankylosing spondylitis has driven the development of clinical algorithms (judiciously using magnetic resonance imaging [MRI]) to identify early disease with a view to initiating appropriate therapy before the development of irreversible damage.
A major deficiency of the earlier classification systems for pediatric chronic arthritis was the failure to adequately distinguish children with arthritis who have, or who might ultimately develop, a spondyloarthropathy, from those with juvenile rheumatoid arthritis. Although the European League Against Rheumatism (EULAR) classification included juvenile ankylosing spondylitis (JAS) and juvenile psoriatic arthritis, these conditions were defined according to adult criteria that require the presence of radiologically identified sacroiliitis or psoriasis, respectively. Children who ultimately develop AS, however, will generally not present with back pain or sacroiliitis (the primary requisites for diagnosing AS in adults). Rather, they typically have peripheral arthritis and a constellation of other features including enthesitis, onset in late childhood, a family history of AS or related diseases, and presence of HLA-B27 antigen. To address these deficiencies, such patients have been variously described as having the syndrome of seronegative enthesopathy and arthropathy (SEA syndrome), pauciarticular-onset juvenile rheumatoid arthritis (JRA) type II, late-onset pauciarticular juvenile chronic arthritis (LOPA), and HLA-B27–associated arthropathy and enthesopathy syndrome. Patients with these various syndromes could also be characterized as having “early” or “undifferentiated” spondyloarthropathy.
The current nomenclature for classification of pediatric chronic arthritis according to the International League of Associations for Rheumatology (ILAR) has encapsulated all of these syndromes in the juvenile idiopathic arthritis (JIA) subcategory of enthesitis-related arthritis (ERA) (see Chapter 198). Enthesitis, the most common defining clinical feature of these syndromes, refers to inflammation (pain, tenderness, and swelling) of the enthesis, the site of attachment of tendon, ligament, or fascia to bone. Thus, children with JAS also fulfill criteria for ERA. As will be discussed under the section “Juvenile Psoriatic Arthritis,” children with arthritis and either psoriasis or psoriatic features probably do not represent a homogeneous subset of children with childhood arthritis despite their current classification within spondyloarthropathies (Table 199-1). Children with IBD associated arthritis or reactive arthritis may or may not develop axial arthritis, and these conditions will also be discussed below.
Table 199-1Comparison of Psoriatic Arthritis, Oligoarthritis, Enthesitis-Related Arthritis, and ...