[Juvenile idiopathic arthritis: Definition and classification]

Area of Science:

• Pediatric Rheumatology
• Immunology
• Genetics

Background:

• Juvenile idiopathic arthritis (JIA) is a heterogeneous group of chronic arthritic conditions affecting children under 16.
• Current international classification categorizes JIA into distinct subtypes (systemic, oligoarticular, polyarticular, enthesitis-related, psoriatic arthritis).
• Existing classifications face challenges with certain JIA subtypes, including systemic-onset JIA, antinuclear factor-positive arthritis, and unclassified cases linked to psoriasis history.

Purpose of the Study:

• To review the current classification of Juvenile idiopathic arthritis (JIA).
• To discuss ongoing debates and challenges in JIA subtyping.
• To highlight the need for improved classification based on pathogenic mechanisms.

Main Methods:

• Review of existing literature and international classification criteria for JIA.
• Analysis of clinical and biological features of different JIA subtypes.
• Discussion of similarities between systemic-onset JIA and autoinflammatory diseases.

Main Results:

• Systemic-onset JIA shares features with autoinflammatory diseases, prompting re-evaluation.
• Antinuclear factor-positive poly- and oligoarticular JIA may represent a more homogenous group.
• Psoriatic arthritis and unclassified arthritis highlight the impact of family history on classification.

Conclusions:

• Enhanced understanding of JIA's pathogenic mechanisms is crucial for refining clinical classification.
• More homogeneous patient groups will improve diagnostic accuracy and treatment strategies.
• Reducing unclassified JIA cases is essential for better patient outcomes.