A case of autoimmune polyglandular syndrome type 3 with plasma glucose and c-peptide levels observed before and after diabetes onset

Changes in metabolic parameters before type 1 diabetes onset remain unclear, so we report the case of a natural history of adult-onset type 1 diabetes. A 59-year-old man with autoimmune polyglandular syndrome type 3 had his plasma glucose and C-peptide levels observed before and after diabetes onset. He was diagnosed with Hashimoto disease in 1991, and LT ₄ replacement therapy was started. Due to weight gain, levels of plasma glucose, C-peptide, and glycosylated hemoglobin were measured since 2002. In 2005, he was hospitalized for diabetic ketoacidosis, and insulin therapy was started. We then confirmed that he was positive for islet-related autoantibodies and diagnosed him with type 1 diabetes.