Brain FDG-PET findings in glutamic acid decarboxylase antibody-associated epilepsy

Glutamic acid decarboxylase antibodies (GAD-Ab) are sometimes associated with chronic drug-resistant focal epilepsy. Clinically, it may manifest as mesial temporal lobe epilepsy (mTLE), with GAD-Ab patients difficult to distinguish. Therefore, the aim of this study is to compare brain metabolism of patients with mTLE and high serum titers of GAD-Ab (>2000 UI/ml) to those with mTLE and hippocampal sclerosis (HS) and confirmed GAD-ab negativity.

Images from PET studies were normalized to an SPM 12 template. Voxel to voxel comparisons were made using a two-sample one-tailed t-test.

In both patients with GAD-Ab and controls (mTLE-HS), hypometabolism in mesial temporal lobe areas was observed. When comparing the two groups, GAD-Ab patients had statistically significant reduced metabolism in both insulae and medial inferior frontal-hypothalamus area (p < 0.001).

Hypometabolism in mesial temporal lobe areas together with hypometabolism in insulae and medial inferior frontal-hypothalamus may be characteristic of patients with epilepsy and GAD-ab. This PET pattern could be a useful diagnostic tool to identify GAD-Ab patients.