Juvenile idiopathic arthritis (JIA) is a rare chronic inflammatory rheumatic disease that begins during childhood and may persist into adulthood in many patients. In addition to joint pain, swelling, and long-term articular damage, chronic inflammatory diseases may also be associated with early sarcopenia, defined as a loss of muscle strength and muscle mass. While this association has been described in adult inflammatory rheumatic diseases, it has not been well studied in patients with JIA.

The aim of this study is to screen for sarcopenia in adolescents and adults with JIA in France. Sarcopenia will be assessed using validated questionnaires, hand grip strength measured with a Jamar dynamometer, and body composition measured by dual-energy X-ray absorptiometry (DEXA). Completion of validated questionnaires will assess nutritional status, fatigue, physical activity, and functional impact. Socio-demographic and clinical data will also be collected from medical records.

This multicenter cross-sectional study will be conducted between June 2026 and October 2027 in 11 French hospitals. Eligible participants are patients aged 15 to 40 years with JIA diagnosed according to ILAR criteria and followed in a French hospital.

This study will provide the first estimate of sarcopenia prevalence among patients with JIA in France. It will also help identify factors associated with sarcopenia and its impact on daily functioning and quality of life. In the longer term, the findings may help clinicians better identify patients at risk and support earlier management focused on disease control, physical activity, and nutritional care.

This is a national multicenter cross-sectional study conducted in 11 French hospitals between June 2026 and October 2027. The study aims to assess sarcopenia in adolescents and adults with juvenile idiopathic arthritis (JIA) during a routine rheumatology follow-up visit.

After receiving study information and providing informed consent (with parental/legal guardian consent for minors, according to applicable regulations), participants will undergo a standardized single study assessment during routine care. This assessment will include measurement of hand grip strength using a Jamar dynamometer, whole-body dual-energy X-ray absorptiometry (DEXA) for body composition and appendicular lean mass evaluation, and completion of validated questionnaires addressing nutritional status, fatigue, physical activity, and functional impact. Additional socio-demographic and clinical data related to JIA history, disease characteristics, and treatments will be collected from medical records.

The study is designed to estimate the prevalence of sarcopenia in patients with JIA in France and to explore factors associated with sarcopenia and its functional impact. If sarcopenia is identified, additional management may be proposed by the treating physician as part of usual care.

inclusion criteria :

• Patients followed in French hospitals participating in the study for juvenile idiopathic arthritis, all forms combined, diagnosed according to the ILAR criteria defined in Edmonton in 2001
• Patients aged 15 to 40 years
• Affiliated to social security
• Agreeing to participate in the study and having given their written consent (signed consent form).

In the case of a minor patient, the consent of the patient and their legal guardians is required.

exclusion criteria :

• Patient under legal guardianship
• Patient not covered by social security
• Pregnant woman
• Inability to perform a functional test required by the study (grip test or whole-body DEXA scan)
• Inability to understand the questionnaires