Autoimmune limbic encephalitis detected on FDG brain scan performed for the evaluation of dementia

Most diagnostic imagers are familiar with the classic patterns of altered metabolism seen in Alzheimer disease, frontal temporal dementia, and dementia with Lewy bodies. However, awareness of other conditions that can cause cognitive impairment is crucial when interpreting FDG brain PET studies. This is particularly true of infectious and inflammatory processes, such as viral encephalitis, which should be diagnosed and treated on an emergent basis. In addition, altered metabolism can be caused by autoimmune paraneoplastic and encephalitic syndromes. We report a case of autoimmune limbic encephalitis encountered as part of evaluation for atypical onset cognitive impairment.