Is temporal lobe epilepsy a progressive disease? Insights from a 5-HT_1A receptor partial volume correction study

Clinical, magnetic resonance (MR) and [¹⁸F]fluorodeoxyglucose positron emission tomography (PET) studies suggest that temporal lobe epilepsy (TLE) might be a progressive disease. Whether epilepsy progression affects 5-HT_1A receptor concentration is still unknown.

We used PET with the 5-HT_1A ligand [¹⁸F]FCWAY in 22 TLE patients. Dynamic frames were acquired for 120-min and modeled with a simplified 3-parameter 2-tissue compartment. An automated, MR-segmentation-based partial volume correction (PVC) algorithm was applied. Contralateral-ipsilateral asymmetry indices (AI) of the binding potential (BP_F = (V_T-V_ND)/f_P) were measured and the effects of epilepsy duration and MR findings were assessed.

In the whole group, there was no significant (P > 0.05) correlation between epilepsy duration and AI in any region. However, in the subgroup of patients (n = 16) with mesial temporal sclerosis (MTS) a significant positive relationship between epilepsy duration and AI was found in hippocampus and parahippocampus. Patients with MTS had significantly greater hippocampus AI than patients with normal MR.

Our results further support the hypothesis that in a subset of patients epilepsy might be 'progressive' by first showing significant correlations between epilepsy duration and 5-HT_1A receptor concentration in hippocampus and parahippocampus of TLE patients with MTS. Loss of 5-HT_1A receptors exceeds loss of gray matter because the relationship between epilepsy duration and 5-HT_1A receptor concentration persists after PVC.