IFIH1 and viral infectious disease: The MDA5 antibody has been tested in some COVID-19 patients and is recognized as an RNA sensor and a key pattern recognition receptor for the SARS-CoV-2 virus.[5] Furthermore, MDA5-DM patients have similar expression levels to those of COVID-19, suggesting the likelihood of viral infection inducing MDA5-DM onset.[6,7] In our case, the patient had a trace of influenza A virus infection on admission, but prolonged immunosuppression use likely enabled overgrowth of various pathogens.