(18)F-FDG PET/CT and MRI findings in a patient with anti-GABA(B) receptor encephalitis.

Autoimmune synaptic encephalitis can occur as paraneoplastic neurological syndromes, which are dysfunctions of the nervous system in cancer patients. One such rare but treatable form is associated with GABAB (γ-aminobutyric acid-B) receptor antibody. We report a 55-year-old man with small cell lung cancer who presented with 3 weeks of progressive seizures, memory impairment, and behavioral disorder. His cerebrospinal fluid anti-GABAB receptor antibody titer was elevated. F-FDG PET/CT revealed pronounced medial temporal hypermetabolism with gross hypometabolism in the rest of the brain. There were no associated abnormalities on MRI. He showed improvement after immunotherapy and chemoradiotherapy.