The Great Still-Usion: Unmasking Adult-Onset Still's Disease Masquerading As Upper Respiratory Tract Infection.

Adult-onset Still's disease (AOSD) is a systemic inflammatory disorder of unknown etiology that presents with high-grade fever, arthritis, evanescent rash, and multiorgan involvement. It is a rare disorder and is a diagnosis of exclusion. AOSD is often misdiagnosed initially as viral exanthems or upper respiratory tract infections leading to a delay in diagnosis. Management includes non-steroidal anti-inflammatory drugs (NSAIDs), glucocorticoids, and conventional or biologic disease-modifying antirheumatic drugs (DMARDs). We report a case of a 53-year-old female with prolonged fever, sore throat, arthralgia, and rash. She was initially presumed to have infectious pharyngitis but did not respond to antimicrobial therapy. After extensive evaluation that excluded infectious, malignant, and other rheumatological etiologies, she was noted to satisfy multiple Yamaguchi criteria and was subsequently diagnosed with AOSD. Glucocorticoids and biologic DMARDs were initiated, leading to improved clinical manifestations and a decline in inflammatory markers.