Spectrum of autoimmune limbic encephalitis on FDG PET/CT

Abstract

To evaluate the role of FDG PET CT in the management of patients with suspected autoimmune encephalitis (AE). A retrospective analysis of 27 patients of clinically suspected cases of AE, who underwent FDG PET CT, was done. The patterns of FDG uptake in different antibody subtypes were recorded and comparison with normalized data was attempted. Post treatment follow-up scans were also acquired and analyzed. Focal areas of hypermetabolism involving medial temporal regions, basal ganglia and thalami with relative global hypometabolism, both on visual inspection and on semiquantitative analysis. Serologically, 17 patients had antibodies against Voltage gated potassium channel (VGKC) complex /LGI1 receptors, 2 had antibodies against CRMP-5 (Anti-CV-2) and 1 had had antibodies against PCA-1/Anti-Yo receptor. We could not isolate the antibody in 7 seven patients. Suspicious mitotic lesions were identified in 10 patients on the whole body scan, which later were biopsied and characterized. No scan evidence of mitotic pathology was identified in 17 patients, thus were labeled as non para neoplastic. Focal hypermetabolism was found to be a feature of acute phase, whereas hypometabolic areas were seen in sub acute and chronic phases of the disease. On follow-up, the post-treatment FDG PET CT scans obtained in some of these patients showed reversal to normal metabolism in the corresponding areas. FDG PET CT may have an important role both in the identification of AE itself and in the detection of the unknown malignancy that might have caused it.