New-onset type 1 diabetes mellitus as a delayed immune-related event after discontinuation of nivolumab: A case report

Immune checkpoint inhibitors (ICIs) have revolutionized cancer treatment. However, they may cause immune-related adverse events. Although there have been a few reports of new-onset type 1 diabetes mellitus (T1DM) during ICI treatment, T1DM as a delayed immune-related event after discontinuing immunotherapy is extremely rare. Herein, we report the case of an elderly veteran who presented with diabetic ketoacidosis 4 months after the discontinuation of treatment with nivolumab. PATIENT CONCERNS: A 74-year-old veteran was treated with second-line nivolumab for advanced non–small cell lung cancer. After 9 treatment cycles, the administration was discontinued due to fatigue. Four months later, he was admitted to the emergency department in a stuporous mental state and hyperglycemia, with high glycosylated hemoglobin levels (10.6%). C-peptide levels were significantly decreased, with negative islet autoantibodies. DIAGNOSES: We diagnosed nivolumab-induced T1DM. There were no laboratory results indicating a new thyroid dysfunction or adrenal insufficiency, which are typical endocrine adverse reactions. INTERVENTIONS: Since the hypothalamic and pituitary functions were preserved and only the pancreatic endocrine capacity was impaired, we administered continuous intravenous insulin injections, with fluid and electrolyte replacement. OUTCOMES: His serum glucose levels decreased, and symptoms improved; hence, on the 8 day of hospitalization, we switched to multiple daily insulin injections. LESSONS: The present case indicates that regular glucose monitoring and patient education are needed for diabetic ketoacidosis after the discontinuation of ICI therapy.