Hyperglycemia With Use of Vagal Nerve Stimulator

Introduction: In patient with diabetes and refractory epilepsy requiring vagal nerve stimulator (VNS), glycemic management can be challenging. Clinical experience is limited in this scenario. Case Report: A 67-year-old male, BMI 30 kg/m2, with history of type 2 diabetes and hemispheric hemangioma complicated by seizure disorder is referred to our diabetes clinic for evaluation of persistent hyperglycemia. The patient reports 25-year history of seizures that have been difficult to control with antiepileptic drugs alone and eventually requiring VNS placement. Patient has normal kidney (eGFR > 60mL/min) and liver function. His antiepileptic drug regimen consisted of gabapentin and as needed lorazepam. He was never on glucocorticoids. Glycated hemoglobin (HgA1c) at our initial evaluation was 10.1%. His anti-glycemic regimen consisted of glipizide monotherapy. Fasting and pre-prandial blood glucose were in the 200-400mg/dL range with occasional values higher than 500mg/dL. This was confirmed with 14-day continuous glucose monitoring that showed average blood glucose of 287mg/dL with 100 percent above target (higher than 180 mg/dL). We optimized therapy by adding once daily glargine, pioglitazone and continued glipizide. At follow up visit, HgA1c still remained high at 10.5%, despite medication adherence. Patient emphasized that hyperglycemia was related to VNS use and given documented hyperglycemia with blood glucose range 500–600 mg/dL when on higher output current of 2 milliamps, his neurologist approved a trial off VNS for 4 weeks. His glucose improved to average less than 200 mg/dL and HgA1c decreased to 9.1% on the same anti-glycemic regimen. Device was re-started due to recurrence of seizures, however the output current and “on time” were reduced to minimal effective range for optimizing seizure therapy while avoiding hyperglycemia. Subsequent HgA1C improved to 8.7%. Discussion: VNS is a FDA approved device for epilepsy and depression. It works by intermittent stimulation or “on/off” periods. In animal studies, elevation of blood glucose was noted with afferent stimulation. Conversely, efferent activation lowers blood glucose. There are limited human studies on the effects of vagal nerve stimulation on glycemic control. The few available, showed variation in blood glucose based on output current and length of on/off period. This should be factored in during glycemic evaluation and management and close collaboration with neurology is essential. Reference: (1) Strauss H, et al. Cervical Vagal Nerve Stimulation Impairs Glucose Tolerance and Suppresses Insulin Release in Conscious Rats. Physiological Reports 2018; 6(24): 1–9 (2) Strauss H, et al. Effect of Vagus Nerve Stimulation on Blood Glucose Concentration in Epilepsy Patients - Importance of Stimulation Parameters. Physiological Reports 2019; 7(14): 1–10