Refractory Urticaria with Raised Antistreptolysin O (ASO) Titer: An Intriguing Case of Adult-Onset Still's Disease.

BACKGROUND Adult-onset Still's disease (AOSD) is a rare systemic autoinflammatory disease with a myriad of clinical presentations. The diagnosis is often challenging because there is no specific confirmatory test. Uncommon presentations can delay the proper diagnosis and management. CASE REPORT A 26-year-old woman presented with a history of urticaria for 2 years that had failed to respond to many types of treatment. Cutaneous biopsy showed neutrophilic urticaria. A diagnosis of AOSD was made after infectious, drug-related, neoplastic, and rheumatic etiologies had been excluded and based on the triad of fever, evanescent rash, and joint pain. Besides leukocytosis and increased levels of inflammatory markers, the patient's laboratory results showed an extremely high D-dimer concentration and an increased antistreptolysin O (ASO) titer. Treatment with prednisolone and methotrexate resulted in resolution of the woman's symptoms. Once clinical remission had been achieved, all laboratory markers returned to normal, yet the patient's ASO titer remained elevated during 18 months of follow-up. CONCLUSIONS Urticaria is a rare cutaneous manifestation of AOSD. Histopathology typically shows predominant neutrophilic infiltrates, which is a unique entity called neutrophilic urticarial dermatosis (NUD). Identifying diseases associated with NUD will facilitate prompt diagnosis and treatment of AOSD, as therapies for it largely differ depending on the underlying cause. Known etiologies of AOS include systemic lupus erythematosus (SLE), Schnitzler syndrome, hereditary autoinflammatory periodic syndromes, and serum sickness-like drug eruption. An elevated ASO titer is unusual, and in our case, it did not seem to follow the patient's clinical course. An elevated D-dimer concentration can be an indicator of disease activity and testing might be beneficial in a subset of patients with normal ferritin levels.