Heidenhain variant sporadic Creutzfeldt-Jakob disease diagnosed as an autoimmune encephalitis due to a false-positive GAD autoantibody.

A 64-year-old man presented with a subacute history progressive visual field defects, illusions and misperceptions. An initial MRI brain revealed a right occipital signal abnormality on diffusion-weighted imaging (DWI) with serum glutamic acid decarboxylase (GAD) autoantibodies markedly elevated. A diagnosis of autoimmune encephalitis was made, with the patient being treated with intravenous immunoglobulin. One month after discharge, the patient represented with worsening frank and well-formed visual hallucinations, ataxia and progressive cognitive impairment. Progress MRI displayed characteristic T2 ribboning on diffusion weighted imaging (DWI) and fluid-attenuated inversion recovery (FLAIR) sequences, along with periodic sharp wave complexes on electroencephalogram (EEG) and a raised CSF protein 14-3-3. Repeat serum, as well as cerebrospinal fluid (CSF), GAD antibodies were again markedly elevated as measured by ELISA (RSR, Cardiff, UK), although archival CSF from the original presentation as well as CSF from the second presentation had undetectable GAD autoantibodies as measured via radioimmunoassay (DIAsource, Ottignies-Louvain-la-Neuve, Belgium). Creutzfeldt-Jakob disease was confirmed at autopsy. © BMJ Publishing Group Limited 2019. No commercial re-use. See rights and permissions. Published by BMJ.