A flare of Still's disease following COVID-19 vaccination in a 34-year-old patient.

Vaccination is a cornerstone for reducing the risk of COVID-19 infection during a pandemic. Although the currently used COVID-19 vaccine is considered safe, some concerns persist regarding the likelihood of flares of rheumatic diseases. Still's disease is a rare auto-inflammatory disorder of unknown etiology, and the data on the flare of Still's disease following COVID-19 vaccination are limited. Therefore, we hereby present the case of a 34-year-old female patient with Still's disease who experienced a flare after a ChAdOx1 nCoV-19 vaccination. The patient visited the emergency department complaining of fever, arthralgia, myalgia, pleuritic chest pain and macular salmon-pink rash on her back for the past 2 days. She had maintained low Still's disease activity with etanercept and low-dose glucocorticoid for 14 years. She received the ChAdOx1 nCoV-19 vaccine 7 days before the flare. Laboratory investigations revealed leucocytosis and elevated serum levels of erythrocyte sedimentation rate, C-reactive protein, and ferritin. Computed tomography showed no specific findings. She received methylprednisolone pulse therapy, etanercept, and methotrexate for treating the Still's disease flare. However, her symptoms were not fully controlled, and she developed pericarditis, pleuritis, fever and macular rashes expanding to her extremities. After excluding infectious conditions by blood culture and pleural fluid analysis, we administered tocilizumab with methotrexate and prednisolone. Her symptoms and laboratory findings improved significantly, and she was discharged without symptoms 7 days later. Although rare, this case of a patient with Still's disease undergoing a flare following vaccination suggests that close observation of disease activity is warranted following COVID-19 vaccination.