Case of new-onset fulminant type 1 diabetes mellitus accompanied by autoimmune thyroid disease after SARS-CoV-2 infection

There is growing evidence suggesting an association between severe acute respiratory coronavirus syndrome coronavirus 2 (SARS-CoV-2) infection and various extrapulmonary diseases since the advent of coronavirus disease 2019 (COVID-19) pandemic. However, case reports of fulminant type 1 diabetes mellitus (FT1D) following SARS-CoV-2 infection are limited. We encountered a 44-year-old Japanese woman who developed FT1D accompanied by subclinical thyrotoxicosis caused by autoimmune thyroid disease (AITD) approximately one week after SARS-CoV-2 infection. The patient developed fever and flu-like symptom 4 days before transportation and tested positive then for the SARS-CoV-2 antigen self-test. She subsequently developed sudden thirst, polyuria, and fatigue of 1 day duration and was urgently brought to our emergency room. Laboratory findings indicated diabetic ketoacidosis (DKA) without marked elevation of serum glycated hemoglobin (HbA1c) levels (glucose, 930 mg/dL; HbA1c, 7.4%). Her insulin secretory capacity was almost completely depleted, and islet-specific autoantibodies were negative. Endocrine examinations revealed subclinical thyrotoxicosis, which was positive for thyroid stimulation hormone receptor antibodies. Based on these results, the patient was diagnosed with FT1D accompanied by AITD and immediately started on intensive insulin therapy with a basal-bolus subcutaneous insulin regimen. Human leukocyte antigen analysis revealed haplotypes, indicating susceptibility to both FT1D and AITD. Further studies are required to elucidate the causal relationship between SARS-CoV-2 infection, FT1D, and AITD. However, clinicians must be vigilant about possible development of FT1D and AITD to enable accurate diagnosis and treatment of patients with DKA during the COVID-19 pandemic.