Temporal lobe epilepsy with isolated amygdala enlargement: anatomo-electro-clinical features and long-term outcome

Background: Temporal lobe epilepsy with isolated amygdala enlargement (TLE-AE) still lacks a definite characterization and controversies exist. Methods: We conducted a retrospective study identifying brain MRI scans with isolated AE between 2015 and 2021. We collected clinical and paraclinical data of patients with TLE-AE and evaluated the outcome. Results: Forty-one subjects were included (20 males; AE: right 13; left 24; bilateral 4). A strong correlation was found between AE and MRI T2-hyperintensity (right: p < 0.005; left: p < 0.003). There was no history of febrile seizures; 85,4% had focal seizures with impaired awareness, 78,1% reported auras (epigastric sensation, déjà-vu, anxiety), 37% had psychiatric disturbances, 48,6% presented with cognitive impairment. We report that AE correlates with FDG-PET temporomesial hypometabolism (right: p = 0.022; left: p = 0.053), temporal interictal activity on EEG (n = 41), and temporal ictal findings during long-term video-EEG monitoring (n = 23). Epilepsy surgery (n = 17) revealed gliosis (n = 4), inflammatory infiltrates (n = 4), or low-grade epilepsy-associated neuroepithelial tumors (n = 5) in the amygdala. Other treatments were immunotherapy (n = 6) and only antiseizure medications (n = 17), with good prognosis (58,1% seizure-free and 17,1% only with auras at last follow-up). There was no correlation between longitudinal changes in seizure frequency and amygdala size (p = 0.848) and T2-hyperintensity (p = 0.909). Conclusions: AE should be searched in TLE patients with typical aura, psychiatric and/or neurocognitive disturbances. The strong correlations found between AE lateralization and neurophysiological, FDG-PET, and MRI data support involvement of AE in the epileptogenic network. Drug resistance should prompt presurgical study. Inflammation in amygdala specimens and response after immunotherapy suggest an immune-mediated etiology in some TLE-AE cases.