Serial 18F-fluoro-2-deoxy-D-glucose Positron Emission Tomography and Magnetic Resonance Imaging of Paraneoplastic Limbic Encephalitis

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Abstract
Objectives To review and expand the existing literature of magnetic resonance imaging (MRI) and positron emission tomography (PET) of paraneoplastic limbic encephalitis (PLE). Methods We performed serial MRI and18F-fluoro-2-deoxy-D-glucose (FDG)–PET in a patient with anti-Ma2–positive PLE. In addition, we reviewed the relevant literature by conducting a search in the MEDLINEdatabase. Results We found a total of 7 published patient studies of possible or probable PLE containing both MRI and PET data. In 1 of these reports, the diagnosis of PLE can be regarded as proven. The results of the previous studies are controversial. Epileptic activity and inflammation are assumed to be underlying mechanisms of increased FDG uptake. In our study, we found a focal tracer accumulation in the left medial temporal lobe, which increased during the first 9 months of follow-up and corresponded with an increase of serum anti-Ma2 antibody titers. The MRI findings showed a hyperintense signal change in the left medial temporal lobe without contrast enhancement, which remained unchanged over time. Conclusions The results of functional and structural imaging in PLE may differ substantially. Results of FDG-PET can demonstrate focal hypermetabolism over a long time, which may indicate therapeutic potential. A prospective study with more patients will be needed to clarify the relevance of PET as a possible outcome measure in PLE. Future studies should include scalp or semi-invasive electroencephalographic recordings during PET acquisition.

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