Rapid Onset of Type 1 Diabetes Mellitus and Destructive Thyroiditis Following Immunotherapy for Metastatic Melanoma.

Background: Immune checkpoint inhibitors, also called immunotherapy, enhance antitumor immunity but may also trigger autoimmune complications due to their mechanism of action. This is a case of rapid-onset multiple endocrinopathies, including type 1 diabetes mellitus and thyroiditis following immunotherapy. Case Report: A 57-year-old male with metastatic melanoma began immunotherapy with nivolumab and ipilimumab. Five weeks later, he was hospitalized with fatigue and abdominal pain. Blood glucose was 607 mg/dL, bicarbonate was 10 mmol/L (reference: 24-30 mmol/L), and arterial pH was 7.21 (reference: 7.35-7.45). Anion gap was 20 mmol/L (reference: 7-16 mmol/L), and beta-hydroxybutyrate was 6.48 mmol/L (reference: 0.02-0.27 mmol/L). His glutamic acid decarboxylase 65 antibody and insulin levels were elevated. His thyroid-stimulating hormone was <0.01 mIU/L (reference: 0.45-4.5 mIU/L), and free thyroxine was 3.1 ng/dL (reference: 0.88-1.77 ng/dL). He was treated for diabetic ketoacidosis and started on subcutaneous insulin. Immunotherapy was resumed at discharge. He later developed severe hypothyroidism requiring supplementation. Discussion: Immune checkpoint inhibitor-induced type 1 diabetes mellitus requires early recognition and management. Thyroid dysfunction is more common in these patients but can become severe and irreversible in the case of inflammatory thyroiditis. Genetic factors may predispose individuals to immune-related adverse events. Conclusion: Close vigilance is essential when using immunotherapy, as endocrinopathies can rapidly onset. In the future, genetic testing might help tailor immunotherapy and monitoring for such adverse events.