Re-Enlightenment of Fulminant Type 1 Diabetes under the COVID-19 Pandemic

Simple Summary From 2019, coronavirus disease 2019 (COVID-19) caused by the novel severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) spread worldwide and became a serious problem. It is known that various viruses are involved in the development of type 1 diabetes (T1D), but the reports of an association between SARS-CoV-2 and T1D are mixed. Fulminant type 1 diabetes (FT1D) is a subtype of T1D mainly reported from East Asia. Autoimmune type 1 diabetes (AT1D) is characterized by chronic pancreatic beta-cell destruction, whereas FT1D is characterized by rapid and almost complete islet destruction following flu-like symptoms, leading to ketoacidosis and, in some cases, sudden death. When discussing the association between COVID-19 and T1D, it is also necessary to focus on FT1D. However, it is not easy to diagnose this subtype without understanding the concept. Therefore, the authors hereby review the concept and latest findings, hoping that the association between COVID-19 and T1D will be adequately evaluated in the future. Fulminant type 1 diabetes (FT1D) is a subtype of type 1 diabetes (T1D) that is characterized by the rapid progression to diabetic ketoacidosis against the background of rapid and almost complete pancreatic islet destruction. The HbA1c level at FT1D onset remains normal or slightly elevated despite marked hyperglycemia, reflecting the rapid clinical course of the disease, and is an important marker for diagnosis. FT1D often appears following flu-like symptoms, and there are many reports of its onset being linked to viral infections. In addition, disease-susceptibility genes have been identified in FT1D, suggesting the involvement of host factors in disease development. In most cases, islet-related autoantibodies are not detected, and histology of pancreatic tissue reveals macrophage and T cell infiltration of the islets in the early stages of FT1D, suggesting that islet destruction occurs via an immune response different from that occurring in autoimmune type 1 diabetes. From 2019, coronavirus disease 2019 (COVID-19) caused by the novel severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) spread worldwide and became a serious problem. Reports on the association between SARS-CoV-2 and T1D are mixed, with some suggesting an increase in T1D incidence due to the COVID-19 pandemic. When discussing the association between COVID-19 and T1D, it is also necessary to focus on FT1D. However, it is not easy to diagnose this subtype without understanding the concept. Therefore, authors hereby review the concept and the latest findings of FT1D, hoping that the association between COVID-19 and T1D will be adequately evaluated in the future.