MRI-negative Temporal Lobe Epilepsy: Is there a Role for PET?

Abstract

MRI-negative PET-positive Temporal Lobe Epilepsy: A Distinct Surgically Remediable Syndrome Carne RP, O'Brien TJ, Kilpatrick CJ, MacGregor LR, Hicks RJ, Murphy MA, Bowden SC, Kaye AH, Cook MJ Brain 2004;127:2276–2285 Most patients with nonlesional temporal lobe epilepsy (NLTLE) will have the findings of hippocampal sclerosis (HS) on a high-resolution MRI. However, a significant minority of patients with NLTLE and electroclinically well-lateralized temporal lobe seizures have no evidence of HS on MRI. Many of these patients have concordant hypometabolism on fluorodeoxyglucose-PET ([18F]FDG-PET). The pathophysiologic basis of this latter group remains uncertain. We aimed to determine whether NLTLE without HS on MRI represents a variant of or a different clinicopathologic syndrome from that of NLTLE with HS on MRI. The clinical, EEG, [18F]FDG-PET, histopathologic, and surgical outcomes of 30 consecutive NLTLE patients with well-lateralized EEG but without HS on MRI (HS–ve TLE) were compared with 30 consecutive age- and sex-matched NLTLE patients with well-lateralized EEG with HS on MRI (HS+ve TLE). Both the HS+ve TLE group and the HS–ve TLE patients had a high degree of [18F]FDG-PET concordant lateralization (26 of 30 HS–ve TLE vs. 27 of 27 HS+ve TLE). HS–ve TLE patients had more widespread hypometabolism on [18F]FDG-PET by blinded visual analysis [odds ratio (OR,+∞(2.51,–); P = 0.001]. The HS–ve TLE group less frequently had a history of febrile convulsions [OR,0.077 (0.002 to 0.512), P = 0.002], more commonly had a delta rhythm at ictal onset [OR,3.67 (0.97 to 20.47); P = 0.057], and less frequently had histopathologic evidence of HS [OR,0 (0 to 0.85); P = 0.031]. No significant difference in surgical outcome despite half of those without HS having a hippocampal-sparing procedure. Based on the findings outlined, HS–ve PET-positive TLE may be a surgically remediable syndrome distinct from HS+ve TLE, with a pathophysiologic basis that primarily involves lateral temporal neocortical rather than mesial temporal structures.