The term juvenile idiopathic arthritis (JIA) is used to cover a group of conditions in childhood from infancy to the age of 17 where arthritis is the main feature and is truly idiopathic (that is, where no definite infective, malignant, hematological or other autoimmune cause is found for the arthritis). There are various subtypes defined in the JIA spectrum, agreed by expert consensus (International League of Associations for Rheumatology (ILAR) criteria) [1
] to be as near to individual disease entities as possible, especially for the purpose of future research into more exact etiologies for these conditions.
Polyarticular JIA is defined as the JIA type where five or more joints are involved with either a rheumatoid factor-positive (on two consecutive tests) or a rheumatoid factor-negative further subdivision [1
]. JIA is said to be polyarticular if at any time in the first 6 months from onset the cumulative number of involved joints reaches five. If this additive total effect only occurs after 6 months from onset then the type is changed from oligoarticular (up to four joints involved) to extended oligoarticular (five or more joints after 6 months). In addition, the JIA subtypes of systemic onset JIA and enthesitis related JIA, as well as psoriatic JIA, can also involve five or more joints. If the other associated defining features of any these particular groups are missing or overlooked, it is possible for a clinical case to be assigned to the incorrect group. Indeed, there may be some false divisions between the various subtypes if polyarticular arthritis is the main feature. However, there are still too few studies with large enough subgroups of patients with all the subtypes to know if the ILAR classification criteria for subtypes is truly clinically relevant from a therapeutic point of view in disease with polyarticular involvement. There is no single diagnostic test for any of the subtypes of JIA apart from a persistently raised rheumatoid factor level in the absence of connective tissues disorders.
The incidence of JIA is approximately 1:10,000, with a prevalence in the population of around 1:1,000 and about one-third of cases being polyarticular in nature [3
]. This subtype may affect from five to most joints, can cause erosive disease, joint deformities with damage to growth plates, reduced mobility and general debility from chronic inflammation. It is associated with long-term disease activity into adult life in over 60% of cases. Treatment to achieve clinical remission is therefore vital, but the exact algorithm of care to achieve full remission has still not been established and there is considerable variation between centers based on clinical experience.
The role of methotrexate in the polyarticular subtype is secure after controlled trials in relatively large numbers of patients [5
]. Biologic therapies including anti-tumor necrosis factor (TNF) blockers have been shown to improve disease activity, but all treatment studies seem to plateau with 75% to 85% of patients responding at significant response levels [8
]. Steroids are used in different ways, with short-term intravenous courses of methylprednisolone or one-off intramuscular depot injections and/or multiple and repeated intra-articular injections being favored by some with others using more long-term regimes of low dose oral steroids [9
]. For difficult unresponsive and damaging disease there are suggestions that Rituximab use may have an important role [12
]. So far, complete and sustained clinical remission allowing for complete withdrawal of treatment is rarely reported, and yet this remains the long-term aim of all treatment attempts [13