What happened, in summary

This 64-year-old man had a history of colon polypectomy, long-term smoking, and alcohol use, but no personal or family history of diabetes. In May 2023, a chest CT scan showed central lung cancer in the left lower lobe with possible obstructive pneumonia. Fiberoptic bronchoscopy and biopsy confirmed extensive-stage small-cell lung cancer. On May 19, 2023, he started serplulimab immunotherapy combined with etoposide and carboplatin. He completed 6 cycles by September 2023, and his glucose levels remained stable during combination treatment. He then continued regular serplulimab monotherapy. On September 18, 2024, he came to the hospital with more than 2 weeks of fatigue, dry mouth, and frequent urination. He was slightly lethargic but afebrile. Blood testing showed severe metabolic acidosis, blood ketones of 7.8 mmol/L, and glucose above the test’s maximum measurable range of 33 mmol/L. HbA1c was 9.6%, fasting C-peptide was very low at 0.03 ng/mL, and post-meal C-peptide was also very low. Autoantibodies linked with type 1 diabetes, including GAD, protein tyrosine phosphatase, zinc transporter 8, and insulin antibodies, were negative. Thyroid testing was also abnormal, supporting an immune-related endocrine complication pattern. He was treated with the standard diabetic ketoacidosis protocol, including intravenous insulin and fluid resuscitation, and he received levothyroxine. Once glucose and ketones were controlled, he transitioned to subcutaneous insulin aspart. He was discharged after 11 days. After discharge, he continued insulin with good glucose control and resumed serplulimab immunotherapy with oral levothyroxine, so both cancer and endocrine care remained active.