Sarcopenia and Juvenile Idiopathic Arthritis

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.

• Sarcopenia screening assessment (Other): Participants will undergo a standardized single-visit assessment including hand grip strength measurement, whole-body DEXA scan for body composition, validated questionnaires, and collection of socio-demographic and clinical data from medical records.

Primary outcomes

• Sarcopenia [Day 1]: A cross-sectional assessment of sarcopenia for each included patient will be performed at a participating hospital center: Performance of a hand grip test using a hand dynamometer (3 consecutive measurements on the dominant hand) and a whole-body DEXA scan with measurement of the appendiceal mass index Confirmation by the best grip test value < -2 SD according to the patient's age and sex on the reference curves associated with a pathological whole-body DEXA (appendiceal mass index ≤ 7 kg/m2 for men, ≤ 5.5 kg/m2 for women)

Secondary outcomes

• Fatigue assessed by FACIT-F [Day 1]: Fatigue assessed using the Functional Assessment of Chronic Illness Therapy-Fatigue (FACIT-F) questionnaire
• Physical activity assessed by IPAQ [Day 1]: Physical activity assessed using the International Physical Activity Questionnaire (IPAQ)
• Functional disability assessed by HAQ-DI [Day 1]: Functional disability assessed using the Health Assessment Questionnaire Disability Index (HAQ-DI).
• Health-related quality of life assessed by SF-12 [Day 1]: Health-related quality of life assessed using the 12-Item Short Form Health Survey (SF-12).

Sex: All, ages: 15 Years to 40 Years

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