Occurrence of adult-onset Still's disease after coronavirus disease 2019 BNT162B2 vaccination in a patient with ulcerative colitis: A case report and review of literature.

Key Clinical Message: We report an extremely rare occurrence of adult-onset Still's disease (AOSD) in a patient with ulcerative colitis. The possibility of autoinflammatory conditions such as AOSD should be considered when evaluating or treating symptoms suspected as side effects of the severe acute respiratory syndrome coronavirus 2 vaccination, regardless of the associated comorbidities. Summary: A woman in her 50s with a history of stable ulcerative colitis (UC) for 20 years, managed using salazosulfapyridine, presented with migratory rashes, spiking fever, edema, and joint pain that started 1 week after receiving the BNT162B2 mRNA vaccine against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Laboratory tests revealed extremely high serum ferritin levels. The patient was diagnosed with adult-onset Still's disease (AOSD) based on the relevant classification criteria after ruling out other diseases. Detection of high levels of interleukin-18, an inflammatory cytokine related to AOSD, supported the diagnosis. Nonsteroidal anti-inflammatory drug monotherapy alone resulted in significant improvements in both the abovementioned symptoms and the elevated inflammatory marker levels. AOSD in a patient with UC is extremely rare. Only one case of AOSD with UC was reported before the coronavirus disease 2019 era. This case indicates that SARS-CoV-2 vaccination can trigger a hyperinflammatory response, classified as AOSD, in a patient with UC, which is extremely rare.