Atypical involvement of the proximal interphalangeal joint in oligoarticular juvenile idiopathic arthritis: a case report.

Introduction and importance: Oligoarticular juvenile idiopathic arthritis (JIA) is the most common JIA subtype, typically involving large joints and presenting as mono- or oligoarthritis within 6 months of onset. Small joint involvement is rare and can complicate diagnosis. Case presentation: We report an 8-year-old Palestinian girl presenting with isolated swelling of the proximal interphalangeal (PIP) joint of the right index finger. She experienced stiffness and restricted motion without systemic symptoms. Initial evaluations, including imaging and biopsy, suggested trauma. Persistent symptoms led to further investigation with magnetic resonance imaging (MRI) and synovial fluid analysis, revealing an inflammatory process. Clinical discussion: Oligoarticular JIA usually affects large joints, making isolated small-joint onset, such as the PIP joint, an uncommon and diagnostically challenging presentation. Similar cases have been reported, highlighting the risk of misdiagnosis as trauma or localized disorders. Our case underscores the importance of considering JIA in persistent monoarthritis and using advanced imaging and synovial analysis to achieve early, accurate diagnosis. Conclusion: Clinicians should consider JIA in cases of persistent monoarthritis, even in small joints, to ensure early diagnosis and appropriate treatment.