Late Onset Temporal Lobe Epilepsy: Possible Etiology and Postsurgical Seizure Outcome

Abstract

Purpose: Patients with temporal lobe epilepsy usually have initial seizures during childhood. Of 256 patients who underwent surgical resection of the temporal lobe, however, 55 (21%) had initial seizures at 16 years of age or older, We tentatively designated these 55 patients the late onset (LO) type. The purpose of this study was to examine the possible etiology and post‐surgical seizure outcome in LO patients compared to patients who had initial seizures at >15 years of age (childhood onset: CO). Methods: Thirty‐four LO patients were inale and 21 were female. Age at seizure onset ranged from 16 to 4.5 years (mean 2 1.3 years). To obtain information on past illness, we retrospectively reviewed the clinical records of all the patients. Status epilepticus was defined as seizures lasting >30 minutes with or without fever. Complex febrilc convulsions were defined according to Nelson. Prior to resection surgery, 30 of 55 LO patients underwent long‐term invasive EEG/video monitoring. Their age at surgery ranged from 17 to 55 years (mcan 33.2 years). Post‐surgical seizure outcome was compared between 46 LO patients and 141 CO patients who had been followed for >2 years after surgery. Results: Thirty‐nine of 55 LO patients (7 I %) had no relevant past illness, but CT/MRI revealed localized lesions in 82% (32/39), comprising dysembryoplastic epithelial tumor (N = 17), focal cortical dysplasia (N = 3), cavernous angionia (N = 10). and arteriovenous malformation (N = 2). The remaining 16 patients had a history of head trauma (N = 6), CNS infection (N = 3), convulsive status (N = 4), complex febrile convulsions (N=I), or nephrosis (N=2). On the contrary, 101 of 201 CO patients (50%) had no relevant past illness, and CTiMRI revealed localized lesions in 44% (44/101), whereas 73 of 201 CO patients (36%) had a history of convulsive status or complex febrile convulsions. Thirty‐three (72%) of 46 LO patients were in Class I of Engel's outcome classification, although 5 of 8 patients with a history of head trauma or CNS infection were in Class I1 ‐ IV. On the contrary, I14 (81%) of 141 CO patients were in Class I, including 8 of 12 with a history of head trauma or CNS infection. Conclusions: I. Approximately 21 %I of patients who underwent surgical resection of the temporal lobe were late onset patients in whom initial seizures begin at 16 years of age or older. 2. Most of the LO patients had no relevant past illness but had localized lesions detected by CT or MRI. 3. The post‐surgical seizure outcome in LO patients was slightly worse than that in CO patients, although the difference was not statistically significant. 4. Surgical indication for LO patients with a history of head trauma or CNS infection should be carefully considered.