A case of type 1 diabetes mellitus with a single-positive zinc transporter 8 antibody who developed diabetic ketoacidosis during chemotherapy for colorectal cancer.

Zinc transporter 8 antibody (ZnT8A) is a key serological marker of type 1 diabetes mellitus (T1DM). Cases of ZnT8A single positivity are relatively rare. This study aimed to investigate a case of ZnT8A single-positive T1DM in a 51-year-old woman who developed diabetic ketoacidosis (DKA) during chemotherapy for colorectal cancer. She had normoglycemia 15 months prior to the presentation. During chemotherapy with intermittent corticosteroid administration, she developed DKA, which required intensive insulin therapy. Although she was negative for glutamic acid decarboxylase antibody (GADA), insulinoma-associated antigen-2 antibody (IA-2A), and insulin autoantibody (IAA), she was positive for ZnT8A. The HLA typing results revealed homozygosity for DRB1*04:06 and DQB1*03:02. At the 6-month follow-up after the initial diagnosis, endogenous insulin secretion remained partially preserved, suggesting an atypical course; the differential diagnosis between acute-onset T1DM with a honeymoon phase and an acute exacerbation of slowly progressive type 1 diabetes mellitus (SPIDDM) remained challenging. Although ZnT8A single-positive T1DM is a relatively uncommon clinical subtype, it should be considered in clinical practice. Previous studies indicated a predominance of acute-onset T1DM in such cases, and even in patients with SPIDDM or an uncertain subtype, there appears to be a potential risk of developing DKA as demonstrated in the present case. Furthermore, given the potential association between ZnT8A positivity and a more rapid deterioration of endogenous insulin secretion, an early assessment of the ZnT8A levels is important when T1DM is suspected.