Background/Purpose: Systemic juvenile idiopathic arthritis (SJIA) is currently classified by the International League of Associations for Rheumatology (ILAR) classification criteria. It is characterized by severe systemic inflammation and is associated with chronic arthritis in many, but not all, patients. Further guidance on the early diagnosis of SJIA is desirable, so that effective treatments can be initiated. The PRO-KIND initiative of the German Society for Pediatric Rheumatology (GKJR) aims to define consensus-based diagnostic and treatment protocols in order to harmonize diagnostic and treatment approaches in Germany. Within PRO-KIND, the first aim of this working group on SJIA was to generate a case definition to be used in the future development and application of consensus-based treatment protocols.

Methods: We retrieved and analyzed data on the clinical characteristics of patients diagnosed with SJIA from two national registries and one cohort in Germany. Subsequently, via online surveys and teleconferences among pediatric rheumatologists with an expertise in the management of SJIA, we identified current diagnostic approaches in Germany. These approaches were harmonized via the formulation of statements, supported by a search of the literature. Finally, a consensus conference using nominal group technique was held to further improve and consent the statements and GKJR case definitions.

Results: De facto only 47.8% and 54.3% (by imputation: 50.4% and 54.7%) of patients diagnosed with SJIA in the AID registry and the ICON-JIA cohort, respectively, fulfill the ILAR classification criteria for SJIA. Statements derived by harmonization indicate that chronic arthritis is not felt to be obligatory for the diagnosis and treatment of SJIA, and that certain biomarkers including S100 proteins are useful for the diagnosis of SJIA. Furthermore, the importance of ruling out competing differential diagnoses is emphasized. Our data support the notion that the Yamaguchi, the newly proposed “Martini classification criteria” and the herein developed GKJR case definition may perform better in classifying patients with SJIA since, in the AID registry and the ICON-JIA cohort, they de facto (by imputation) classify 55.1%/77.1% (69.3%/82.1%), 71.0%/71.4% (65.0%/77.7%) and 62.3%/65.7% (78.3%/68.0%) as SJIA, respectively.

Conclusion: We developed evidence-informed, consensus-based statements regarding the diagnosis of SJIA in Germany. These statements should prove useful for application in clinical practice and the implementation of consensus treatment protocols, which are developed in the PRO-KIND initiative. We developed case definitions rather than classification criteria since a delay of diagnosis may lead to delayed treatment and serious complications in case of SJIA. We therefore embrace the development of new classification criteria for SJIA to better reflect the entire spectrum of patients with SJIA and allow appropriate categorization of patients and access to clinical trials.