Two cases of immune checkpoint inhibitor-associated diabetes mellitus induced by serplulimab: Case reports

Immune checkpoint inhibitors have shown promising efficacy in treating various malignancies; however, their use is associated with immune-related adverse events, including rare but severe immune checkpoint inhibitor-induced diabetes mellitus (ICI-DM). Serplulimab-induced ICI-DM has been rarely reported, and its clinical presentation can be heterogeneous.

We report 2 patients with small cell lung cancer who developed serplulimab-induced ICI-DM, both complicated by diabetic ketoacidosis (DKA). Case 1 developed delayed-onset ICI-DM after 2 years of treatment, with elevated glycated hemoglobin and moderate C-peptide deficiency. Case 2 developed ICI-DM earlier, with severe insulin deficiency and classic type 1 diabetes features. Neither patient tested positive for diabetes-related autoantibodies.

Both patients were diagnosed with serplulimab-induced ICI-DM, confirmed by hyperglycemia, C-peptide deficiency, and DKA during ongoing programmed cell death protein 1 inhibitor therapy.

Standard DKA management was administered for both patients. They were transitioned to subcutaneous insulin therapy and continued serplulimab treatment under close glucose monitoring.

Both patients' DKA was successfully controlled. They continued serplulimab and insulin therapy after discharge, with no recurrence of acute DKA.

These cases highlight the clinical heterogeneity and diagnostic challenges of ICI-DM. Routine blood glucose and glycated hemoglobin monitoring before and during immunotherapy may aid early detection. Clinicians should maintain a high index of suspicion for ICI-DM, even in patients without typical risk factors. Early recognition and insulin initiation are essential to prevent life-threatening complications of DKA. This report contributes to the limited literature on serplulimab-induced ICI-DM and provides practical insights into its diagnosis and management.