Limbic encephalitis investigated by (18)FDG-PET and 3D MRI

patients with clinically probable or possible limbic encephalitis (LE) are reported, both cases with typical findings in clinical symptoms (severe neu ropsychological deficits and complex partial seizures) and in routine magne tic resonance imaging (MRI) (hyperintense mesiotemporal lesions). Underlyin g malignancy was identified (rectal carcinoma) in one case but could not be detected in the other patient. The 2 patients were investigated by cerebra l F-18-fluoro-2-deoxy-D-glucose-positron emission tomography (FDG-PET) and 3-dimensional (3D) MRI, and abnormalities in metabolic activity were mapped using coregistration of spatially normalized PET and MRI. Highly significa nt focal hypermetabolism in bilateral hippocampal areas was found in both c ases. The authors' findings support FDG-PET coregistered to 3D MRI as a pot entially valuable additional tool in the imaging diagnostics of LE. Results are discussed with respect to the clinical symptoms and previously reporte d imaging findings in the disease.