Potassium channel antibody-associated encephalopathy presenting with a frontotemporal dementia-like syndrome

Objective: To describe a patient who presented with features suggestive of frontotemporal dementia (FTD) but with some atypical findings and antibodies to neuronal voltage-gated potassium channels (VGKC-Abs). Design: Case report. Setting: Mater Misericordiae University Hospital, Dublin, Ireland. Results: An 82-year-old man presented with progressive changes in personality, social conduct, and executive function with preservation of memory, deteriorating from baseline to requiring acute hospitalization within 6 months. Transient deterioration (episodic speech arrest) with spontaneous recovery, atypical for frontotemporal dementia, was observed. The patient had an elevated VGKC-Abtiter (2624 pM [normal range, <100 pM]), elevated protein levels in cerebrospinal fluid, and a negative evaluation for malignancy. Magnetic resonance imaging of brain was normal but [¹⁸F]-fluorodeoxyglucose positron emission tomographic imaging revealed bifrontal hypometabolism. A marked and sustained improvement with steroid therapy was observed. Conclusion: Workup for a potentially reversible autoimmune-mediated encephalopathy, including a VGKC-Ab titer, should be considered in patients presenting with rapidly progressive behavioral and cognitive decline.