The progression of initial symptoms and its relationship with the clinical course in adult-onset Still's disease: from the KEIO-AOSD cohort.

Objectives: Adult-onset Still's disease presents with nonspecific and heterogeneous features. This study aims to elucidate the development of initial symptoms and their relationship with the disease course in adult-onset Still's disease. Methods: We retrospectively reviewed consecutive patients with adult-onset Still's disease who had been enrolled in the KEIO-AOSD cohort from April 2012 to July 2024. Clinical information was collected from their medical records. Detailed initial symptoms and their relationship with disease courses were analyzed. Results: A total of 89 patients were included. The mean age at diagnosis was 46.3 ± 18.5 years, and 73.0% were females. The median time from the onset of initial symptoms to the first clinic visit, the first blood testing, satisfaction of Yamaguchi's criteria, and treatment initiation were 5.0, 10.0, 21.0, and 35.0 days, respectively. As initial symptoms, fever, was observed in 50.6%, rash and arthralgia in 37.1% each, and sore throat in 30.3%. Fever and sore throat rapidly increased within 2 weeks prior to Yamaguchi's criteria satisfaction. Patients with rash as an initial symptom tended to experience a delay in taking blood testing and satisfying Yamaguchi's criteria. Patients presenting with a sore throat as an initial symptom tended to show higher ferritin levels and experience macrophage activation syndrome. No significant differences were observed in long-term outcomes. Conclusions: Early clinical courses of adult-onset Still's disease varied depending on initial symptoms. Focusing on initial symptoms in clinical practice can contribute to earlier diagnosis and better management.