Juvenile Idiopathic Arthritis (JIA) is a chronic condition that causes joint inflammation in children. In some cases, the inflammation also affects the protective sheath surrounding the tendons, a condition known as tenosynovitis. Because tenosynovitis can be difficult to distinguish from regular joint swelling during a standard physical exam, specialized imaging tools like ultrasound are highly useful for an accurate diagnosis.

This observational study aims to determine how frequently tenosynovitis occurs in children and adolescents diagnosed with two specific subtypes of the disease: polyarticular and oligoarticular JIA.

Researchers will evaluate participants up to 16 years of age receiving care at Assiut University Children Hospital. During the study, patients will undergo a standard clinical assessment, which includes a medical history review and a thorough physical examination of their joints and tendons. Routine laboratory blood tests will also be reviewed. To precisely detect any hidden tendon inflammation, doctors will perform a musculoskeletal ultrasound, which is a safe, radiation-free imaging procedure, on major tendon and joint sites. By comparing the clinical exams with the ultrasound findings, researchers hope to improve the early recognition and management of tendon inflammation in pediatric JIA patients.

Juvenile Idiopathic Arthritis (JIA) encompasses a heterogeneous group of diseases characterized by chronic joint inflammation. While synovitis is the hallmark of JIA, tenosynovitis is a frequent yet often under-recognized manifestation that can significantly contribute to a patient's clinical burden. Clinical examination alone is frequently insufficient to distinguish true tenosynovitis from joint synovitis or soft tissue edema, particularly in pediatric patients with ankle involvement. Consequently, Musculoskeletal Ultrasound (MSK-US) has emerged as a critical tool for identifying peritendinous fluid and sheath thickening, allowing for targeted therapeutic interventions such as ultrasound-guided steroid injections.

This cross-sectional observational study is designed to systematically evaluate the clinical and sonographic characteristics of tenosynovitis in pediatric patients diagnosed with polyarticular and oligoarticular JIA.

Enrolled participants will undergo a comprehensive single-visit evaluation consisting of the following components:

• Clinical Evaluation: A detailed medical history will be recorded, including age of arthropathy onset, detailed therapeutic history, and family history of genetic, metabolic, or skeletal disorders. A thorough musculoskeletal physical examination will evaluate the number of tender and swollen joints, specific enthesitis sites, localized tendon tenderness or swelling, and overall functional status.
• Laboratory Investigations: Routine baseline laboratory tests will be collected, including Erythrocyte Sedimentation Rate (ESR), C-Reactive Protein (CRP), Complete Blood Count (CBC), Rheumatoid Factor (RF), Antinuclear Antibody (ANA), and Anti-cyclic citrullinated peptide antibodies (Anti-CCP) if clinically indicated.

To detect both clinical and subclinical tenosynovitis, patients will undergo a standardized MSK-US examination using a high-frequency linear probe.

• Targeted Sites: High-resolution B-mode and Power Doppler (PD) ultrasound will examine major entheseal sites including the Achilles tendon insertion, plantar fascia, patellar tendons, and quadriceps tendon insertions. Specific attention will be given to the tendon sheaths of the tibialis posterior, peroneus longus, and peroneus brevis.
• Ankle Protocol: The ankle region will be scanned using anterior, perimalleolar medial, and lateral approaches to ensure comprehensive visualization.
• Sonographic Assessments: The ultrasound will evaluate enthesis thickness, hypoechogenicity, tendon sheath effusion, synovial hypertrophy, and Power Doppler signals indicating active inflammation.
• Diagnostic Criteria for Tenosynovitis: Tenosynovitis will be sonographically diagnosed by the presence of hypoechoic or anechoic thickened tissue detected in two perpendicular planes. The presence of fluid within the tendon sheath and an active Doppler signal will serve as confirmatory markers of active inflammation.

Inclusion Criteria:

• Children and adolescents (typically under 16 years of age at the time of onset) diagnosed with Juvenile Idiopathic Arthritis (JIA).
• Patients of both genders.
• Patients or their legal guardians who provide written informed consent/assent to participate in the study.

Exclusion Criteria:

• Patients more than 16 years of age.
• Patients with arthritis secondary to other known causes (e.g., trauma, infectious arthritis, malignancy, or other systemic autoimmune diseases like Systemic Lupus Erythematosus).
• Patients with a history of major orthopedic surgery at the examined entheseal sites.
• Active infection or metabolic disease that may affect musculoskeletal structures.
• Patients who decline participation or fail to provide informed consent.

The study population consists of children and adolescents under 16 years of age diagnosed with either the polyarticular or oligoarticular subtypes of Juvenile Idiopathic Arthritis (JIA). Participants will be recruited from the inpatient wards and the outpatient clinic of the Allergy, Immunology, and Rheumatology unit at Assiut University Children Hospital over a two-year period.