Severe Hyperglycemia Due to Protein Kinase Inhibitor Therapy in a Patient With Poorly Controlled Diabetes Mellitus

The efficacy and safety of zanubrutinib, a highly selective next-generation Bruton's tyrosine kinase (BTK) inhibitor, in chronic lymphocytic leukemia and lymphoplasmocytoides immunocytoma seems favorable. Adverse events comprise neutropenia, thrombocytopenia, infection, anemia, and atrial fibrillation. This report describes a 75-year-old man suffering from polydipsia, polyuria, and blurred vision for 10 days. He was diagnosed with lymphoplasmocytoides immunocytoma in 2003. After various therapies, he was started on zanubrutinib in October 2022. A diagnosis of diabetes mellitus had never been established before. On arrival in the emergency department, his plasma glucose was 37.2 mmol/L (671 mg/dL) and glycated hemoglobin (HbA1c) was 14.2%. Circulating antibodies showed positivity for glutamic acid decarboxylase (GAD-65), and his C-peptide level was 1.3 nmol/L (normal range, 0.37-1.47 nmol/L), equivalent to 3.9 ng/mL (normal range 1.1-5.0 ng/mL). From the patient's medical history, it became obvious that the metabolic situation had been problematic for many years, and that diabetes could have been taken into account at least in the summer of 2020 when HbA1c was 6.7%. In patients on tyrosine kinase inhibitors, careful assessment of glycemic control (monitoring HbA1c and blood glucose levels periodically even for nondiabetic patients) is recommended to prevent a major diabetic emergency.