Background: In some patients with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection (coronavirus disease 2019 [COVID-19]), an uncontrolled release of inflammatory cytokines is characteristic. COVID-19 and adult-onset Still’s disease (AOSD) have been included by some authors in the “hyperferritinemic syndromes.” Another hyperinflammatory syndrome (with variable features of Kawasaki disease) called multisystem inflammatory syndrome (MIS) has been described in patients who have had SARS-CoV-2 infection. Case Presentation: We present a previously healthy patient who developed hyperinflammatory reaction compatible with MIS; the clinical presentation is additionally compatible with AOSD, complicated with a mild myocarditis. The patient had a positive SARS-CoV-2 serology (immunoglobulins G and immunoglobulins M ), but multiple reverse transcription-polymerase chain reaction (RT-PCR) testing for SARS-CoV-2 on nasopharyngeal swab were negative or indeterminate, so we considered that it is possible that an asymptomatic SARS-CoV-2 infection could have been the trigger for Still’s disease. 24 hours after starting methylprednisolone treatment, the fever was resolved and symptoms improved over the next few days, with persistent arthralgias. Conclusion: Asymptomatic SARS-CoV-2 infection could trigger MIS with AOSD-like features.

Keywords: SARS-CoV-2, COVID-19, adult-onset Still’s disease (AOSD), myocarditis, hyperferritinemic syndromes, multisystem inflammatory syndrome (MIS), multisystem inflammatory syndrome of children (MIS-C), case report