The programmed cell death-1 (PD-1) pathway is a novel therapeutic target in immune checkpoint therapy for cancer. Nivolumab, an anti-PD-1 monoclonal antibody, blocks PD-1 and can restore anti-cancer immune responses by disrupting the signal that inhibits T-cell activation. Nivolumab may induce endocrinerelated adverse events, including hypophysitis, autoimmune thyroiditis, and type 1 diabetes mellitus. Here we report a 68-year-old female patient with advanced renal cell carcinoma who was treated with nivolumab. She had positive anti-thyroglobulin antibodies and anti-thyroid peroxidase antibodies with slightly elevated thyroid-stimulating hormone (9.048 μU/mL), and was diagnosed as chronic thyroiditis with subclinical hypothyroidism before nivolumab therapy. She developed painless thyroiditis after the first cycle of the therapy (Day 14). At the 7th cycle of nivolumab therapy (Day 98), hyperglycemia (473 mg/dL) was noted, whereas glycated hemoglobin level was 6.9%. Islet-related autoantibodies were all negative. The glucagon tolerance test showed complete depletion of insulin. Human leukocyte antigen typing showed haplotype DRB1*09:01-DQB1*03:03, which was reported to be closely associated with type 1 diabetes mellitus in Japan. Fulminant type 1 diabetes mellitus was diagnosed, and she was immediately treated with multiple daily injections of insulin. Fulminant type 1 diabetes mellitus is characterized by rapid-onset diabetic ketoacidosis, and negative islet-related autoantibodies, and was proposed as a novel subtype of non-autoimmune diabetes. Preceding painless thyroiditis with positive thyroid autoantibodies observed in the present case, however, raises the possibility that autoimmune mechanisms are involved in the pathogenesis of nivolumab-induced fulminant type 1 diabetes mellitus.

The epidemic of coronavirus disease‐2019 (COVID‐19) is the major public health issue in the world. COVID‐19 vaccines are one of the most effective strategies against COVID‐19. Here we report a 36‐year‐old female patient who had thirst, polydipsia, polyuria, palpitations, loss of appetite, and fatigue 3 days after the first dose of COVID‐19 RNA‐based vaccines without a prior history of diabetes. Ten days after vaccination, she visited our hospital with diabetic ketoacidosis and was diagnosed with type 1 diabetes. Hyperglycemia (501 mg/dL), anion gap metabolic acidosis and ketonuria were observed. The glycated hemoglobin level was 7.0%. Islet‐related autoantibodies were all negative. The glucagon tolerance test revealed attenuated secretion of insulin. Human leukocyte antigen was haplotype DRB1*0405‐DQB1*0401, which was associated with type 1 diabetes in Japan. The present case suggests that COVID‐19 RNA‐based vaccines might trigger the onset of type 1 diabetes, even in subjects without prior histories of diabetes.

Central diabetes insipidus (CDI) is a rare condition caused by various underlying diseases including inflammatory and autoimmune diseases, and neoplasms. Obtaining an accurate definitive diagnosis of the underlying cause of CDI is difficult. Recently, anti-rabphilin-3A antibodies were demonstrated to be a highly sensitive and specific marker of lymphocytic infundibuloneurohypophysitis (LINH). Here, we report a detailed case series, and evaluated the significance of anti-rabphilin-3A antibodies in differentiating the etiologies of CDI. A prospective analysis was conducted in 15 consecutive patients with CDI from 2013 to 2020 at a single referral center. Anti-rabphilin-3A antibodies were measured and the relationship between antibody positivity and the clinical/histopathological diagnoses was evaluated. Among 15 CDI patients, the positive anti-rabphilin-3A antibodies were found in 4 of 5 LINH cases, 3 of 4 lymphocytic panhypophysitis (LPH) cases, one of 2 sarcoidosis cases, and one intracranial germinoma case, respectively. Two Rathke cleft cyst cases and one craniopharyngioma case were negative. This is the first report of anti-rabphilin-3A antibodies positivity in CDI patients with biopsy-proven LPH. Measurement of anti-rabphilin-3A antibodies may be valuable for differentiating CDI etiologies.