Abstract
Blau syndrome is a rare granulomatous autoinflammatory disease caused by NOD2 mutations and characterised by dermatitis, arthritis and uveitis. We report a middle childhood boy initially diagnosed with oligoarticular juvenile idiopathic arthritis (JIA) because arthritis was the predominant early manifestation. He had papular skin lesions in infancy and periarticular swelling and tenosynovial cysts, later developed persistent arthritis and recurrent fever. Genetic testing identified a heterozygous NOD2 variant (c.1001G>A, p.Arg334Gln [R334Q]), confirming Blau syndrome. Despite ongoing methotrexate and adalimumab therapy, routine ophthalmic examination revealed unilateral anterior uveitis with iris nodules. Fundus examination showed bilateral multifocal chorioretinal lesions, and fluorescein angiography demonstrated retinal vasculitis. Ocular inflammation became quiescent after topical corticosteroid treatment and weight-based escalation of adalimumab. This case highlights that Blau syndrome may masquerade as JIA and that regular ophthalmic surveillance remains essential even during biologic therapy.