Abstracts

Rationale: Cases of MRI-negative and lesional TLE are similar in their seizure semiology and electroclinical profile, suggesting similar underlying network disturbance. It remains unclear, however, whether they are also similar in their neuropsychological profiles, as previous studies have generally been low powered and report mixed findings. This study aims to clarify the contribution of a lesion on memory and mood functioning, hypothesising neuropsychological impairment in nonlesional TLE relative to controls, with greater impairment in lesional cases. Methods: Overall, 152 adults participated: 79 TLE patients and 73 sociodemographically-matched healthy controls. On the basis of clinical MRI, 19 (24%) of the patients had a lesion consistent with hippocampal sclerosis (HS-TLE), 30 (38%) had a lesion other than HS (MRI-pos TLE), and 30 patients (38%) did not have a detectable lesion and were deemed lesion negative (MRI-neg TLE). Memory and mood were assessed using gold-standard psychometric measures commonly used in epilepsy. Results: Relative to controls, patients with MRI-neg TLE showed significantly impaired autobiographical, verbal, and visual memory (strong effect sizes); they also reported significantly more symptoms of depression and anxiety. Contrary to expectations, the three TLE subgroups showed no significant differences in cognitive or mood functioning. The memory impairments of the nonlesional group were predicted by clinical, cognitive, and psychiatric factors such as a past history of depressive disorder, lower IQ, and earlier age at onset of seizures. Conclusions: MRI-negative TLE is associated with memory and mood dysfunction equivalent to that seen in patients with hippocampal sclerosis and other structural pathologies. These findings suggest that neuropsychological impairments in TLE are not contingent upon a macroscopic structural lesion, and might be better conceptualised as an intrinsic property of the underlying network disease. Funding: N/A