Extensive and temporally ungraded retrograde amnesia in encephalitis associated with antibodies to voltage-gated potassium channels

Background: Encephalitis associated with antibodies to voltage-gated potassium channels (VGKC-Ab) is characterized by epilepsy, behavioral changes, and anterograde memory impairment. Magnetic resonance imaging reveals abnormal signal predominantly restricted to the mediotemporal lobes. Objective: To determine the temporal extent and potential reversibility of retrograde amnesia in 3 patients with VGKC-Ab-associated encephalitis. Design: Case report. Setting: Clinical. Patients: Three patients diagnosed as having VGKC-Ab-associated encephalitis underwent cognitive testing before and after immunotherapy. Main Outcome Measures: In addition to standard neuropsychological tests, retrograde memory was assessed using 2 novel tests. Memory for past newsworthy events was assessed using a public events test; test material was divided into epochs of 5 years and spanned approximately 25 years. This was complemented by a famous faces test in which patients were required to identify individuals from the recent and remote past. Results: All 3 patients were found to have temporally ungraded retrograde amnesia dating back more than 20 years. Magnetic resonance imaging in all patients revealed high-signal abnormalities predominantly affecting the hippocampi. Subsequent testing performed after immunotherapy revealed subjective improvement but no evidence of a temporal gradient in the recovery of past memories. Conclusions: Encephalitis associated with VGKC-Ab results in extensive and temporally ungraded retrograde amnesia that is partially reversible with immunotherapy. Magnetic resonance imaging high-signal abnormalities were primarily restricted to the hippocampi. These data are supportive of theories postulating a role for the hippocampus in the storage and retrieval of all past memories, irrespective of age, rather than theories of memory consolidation that propose an involvement of the hippocampus only in the temporary storage of memories.