To present a case of a new onset intermittent left bundle branch block (LBBB) worsened by ictal tachycardia in an elderly male patient with anti-leucine-rich glioma-inactivated 1 (LGI1) encephalitis.

LGI1 encephalitis is the second most common immune-mediated encephalitis. It can manifest with focal seizures (faciobrachial dystonic and/or autonomic seizures), memory impairment, psychiatric disturbances, and dysautonomia. LGI1 encephalitis commonly affects male older individuals, a sub-group at increased risk for cardiac disease. Cardiac bradyarrhythmias have been reported in association with LGI1 encephalitis. Tachycardia-associated conduction abnormalities have not been reported.

A 74-year-old male presented to the University of Florida in Jacksonville after a first focal to bilateral tonic-clonic seizure. He also reported memory impairment over the previous year and episodic epigastric rising sensations with nausea, lasting seconds long. He was discharged on levetiracetam monotherapy; however, focal preserved consciousness (FPC) seizures persisted. He was therefore admitted to the Epilepsy Monitoring Unit where multiple independent left>right temporal seizures were captured. Seizures induced tachycardia with a notable worsening of a left bundle branch block, mimicking ventricular tachycardia. Serial EKGs showed normal sinus rhythm with an intermittent LBBB. Cardiology evaluation found no structural or ischemic heart disease. There were no electrolyte abnormalities. MRI brain showed T2/FLAIR hyperintensities at the left mesial temporal lobe. Serum and CSF testing identified LGI1-IgG antibodies. Oncologic work-up was negative. The FPC seizures and ictal-related cardiac issues resolved with the addition of oxcarbazepine and intravenous methylprednisolone.

Seizures can be associated with life-threatening cardiac arrhythmias and conduction abnormalities. LGI1 encephalitis commonly occurs in a vulnerable older population already at increased risk for cardiac disease and can lead to conduction abnormalities, by way of potassium channel dysfunction. Early identification of peri-ictal cardiac phenomena that can impact morbidity and mortality is important when caring for a patient with LGI1 encephalitis.