Role of MR and PET in anti-voltage gated potassium channel (anti-VGKC-ab) antibody limbic encephalitis: A challenge ahead for simultaneous PET/MR

Objectives Anti-VGKC-antibodies cause hyper-excitability of the peripheral and central nervous system. Clinical manifestations include episodic memory impairment, disorientation and agitation. It is auto-immune and potentially treatable. We aim to evaluate the role of combine MR and PET in this rare entity.

Methods We evaluated 6 cases of Anti-VGKC-ab referred for anatomical and metabolic imaging. MR of brain (T1, T2, FLAIR) and 18F FDG PET/CT scans of the whole body including brain were obtained. Patient’s demographics, VGKC levels, structural abnormalities on MRI and metabolic alterations were evaluated on 18F FDG PET/CT.

Results There were 5 male and 1 female patients (age range 55-76 years). The voltage gated potassium channel antibody levels were 298-5757 pM (normal range 0-100 pM). MRI showed following anatomical abnormalities: Increased signal on FLAIR in the hippocampi, punctiform whiter matter changes, cortical volume loss, increased T2 signal in the anterior temporal lobes, abnormal signal in the basal ganglia, hippocampal atrophy and increased T2 signal/FLAIR in the anterior limb of internal capsule. 18F FDG PET/CT showed following areas of altered cerebral metabolism Generalised hypometabolism in the temporal lobes, focal hypermetabolism in the medial temoral lobe and mild hypometabolism in the parietal lobes.

Conclusions Both MR and PET compliment the diagnostic yield in anti VGKC-antibody associated limbic encephalitis. Simultaneous PET/MR will facilitate early diagnosis and lesion characterization