Literature data suggest that elevated blood values of IL-18 and IL-18 Binding Protein and alterations in their ratio may be significantly correlated with various autoinflammatory diseases, such as systemic juvenile idiopathic arthritis, recurrent autoinflammatory fevers etc. In this view, the clinical implication of this observational, prospective, single-centre, non-pharmacological study will be the definition of new laboratory markers that may be useful in the early differential diagnosis of certain rare and serious paediatric diseases.

The primary aim of this study is to investigate the role of IL-18 and IL-18 Binding Protein as biomarkers of systemic Juvenile Idiopathic Arthritis and recurrent autoinflammatory fevers, while the secondary one is to investigate the superiority of IL-18 and IL-18 Binding Protein over other cytokines and inflammatory indexes in the differential diagnosis of systemic Juvenile Idiopathic Arthritis and recurrent fevers of an autoinflammatory nature.

The study will enroll patients referred to the Pediatric Rheumatology Outpatient Clinic of the Pediatrics Unit, IRCCS Azienda Ospedaliero-Universitaria of Bologna, Italy, for suspected Juvenile Idiopathic Arthritis or suspected recurrent fever/self-inflammatory disease.

Patients will be enrolled during the acute phase of the disease and, prior to the start of immunosuppressive therapy (i.e. corticosteroids, colchicine, biological drugs), a blood sample will be taken for haematochemical investigations, according to clinical practice, as well as an additional blood sample for the assay of IL-18 and IL-18 Binding Protein.

The following variables will be considered for each patient: demographic data; key clinical features; haemochromocytometric test; liver and kidney function tests; indexes of inflammation and acute phase proteins; inflammatory cytokines panel; serum values of IL-18 and IL-18 Binding Protein.

Inclusion Criteria:

• Age between 2 years and 18 years;
• Being affected by 1 of the following: Juvenile Idiopathic Arthritis; recurrent fever/ autoinflammatory disease; rheumatic disease; severe infectious diseases (sepsis, meningitis, urinary tract infection, lower respiratory tract infection);
• Obtaining informed consent from parents/legal guardians of paediatric patients.

Exclusion Criteria:

• Patients in whom the suspicion of rheumatic disease is based on a finding of subclinical carditis or chorea.

The study enrolls patients referred to the Pediatric Rheumatology Outpatient Clinic of the Pediatrics Unit, IRCCS Azienda Ospedaliero-Universitaria of Bologna, Italy, for suspected Juvenile Idiopathic Arthritis or suspected recurrent fever/self-inflammatory disease.