Chronic Adult-Onset Still's Disease With Positive Antinuclear Antibodies: Navigating Diagnostic Dilemmas and Clinical Implications.

Adult-onset Still's disease (AOSD) is a rare systemic autoinflammatory disorder characterized by fever, rash, and joint pain. Despite primarily affecting young adults, it can occur at any age, presenting diagnostic challenges due to its heterogeneous nature and lack of specific laboratory findings. The subset of AOSD with positive antinuclear antibody (ANA) adds complexity, potentially overlapping with other autoimmune conditions. We describe a case of a 30-year-old female with a two-year history of fever, weight loss, and joint pain, initially misdiagnosed as seronegative arthritis with hypothyroidism. Further evaluation revealed severe anemia, leucocytosis, and hepatosplenomegaly. Despite a strongly positive ANA, the absence of systemic lupus erythematosus (SLE) features led to a diagnosis of chronic AOSD. Treatment with steroids and disease-modifying antirheumatic drugs (DMARDs) resulted in clinical improvement, highlighting the importance of accurate disease classification for tailored management in ANA-positive AOSD. This case underscores the diagnostic challenges of AOSD and emphasizes the need for precise classification for optimal treatment strategies.