Uncommon Bilateral Frontoparietal Cortex Hypermetabolism Revealed by 18F-FDG PET/CT in a Patient With Anti-LGI1 Encephalitis

Limbic hypermetabolism is a frequently observed manifestation of anti-LGI1 encephalitis on 18 F-FDG PET/CT imaging. In this case report, we present an atypical finding on 18 F-FDG PET/CT in a patient with anti-LGI1 encephalitis and negative MRI results. Apart from the expected hypermetabolism in the bilateral limbic system, there was also an uncommon intense uptake of 18 F-FDG noted in the bilateral frontoparietal cortex. Subsequent follow-up scans demonstrated normalized metabolism following treatment. The case highlights that neocortical hypermetabolism can be a characteristic feature of active anti-LGI1 encephalitis on 18 F-FDG PET/CT imaging.