The putative mechanism of vagus nerve stimulation (VNS) for medically refractory epilepsy is desynchronization of hippocampal and thalamocortical circuitry; however, the nature of the dose-response relationship and temporal dynamics is poorly understood. For greater elucidation, a study in a nonepileptic rat model was previously conducted and showed that rapid-cycle (RC) VNS achieved superior desynchrony compared to standard-cycle (SC) VNS. Here, the authors report on the first in-human analysis of the neuromodulatory dose-response effects of VNS in a patient with posttraumatic, independent, bilateral mesial temporal lobe epilepsy refractory to medications and SC-VNS who was referred as a potential candidate for a responsive neurostimulation device. During stereotactic electroencephalography (SEEG) recordings, the VNS device was initially turned off, then changed to SC-VNS and then RC-VNS settings. Spectral analysis revealed a global reduction of power in the theta (4–8 Hz) and alpha (8–15 Hz) bands with both SC- and RC-VNS compared to the stimulation off setting (p < 0.001). Furthermore, in the alpha band, both SC- and RC-VNS were associated with greater global desynchrony compared to the off setting (p < 0.001); and, specifically, in the bilateral epileptogenic hippocampi, RC-VNS further reduced spectral power compared to SC-VNS (p < 0.001). The dose-response and temporal effects suggest that VNS modulates regional and global dynamics differently.
Adeel Ilyas, Emilia Toth, Diana Pizarro, Kristen O. Riley, and Sandipan Pati
Sandipan Pati, Adib A. Abla, Harold L. Rekate, and Yu-Tze Ng
Hypothalamic hamartomas (HHs) often cause pharmacoresistent epilepsy, incapacitating behavioral abnormalities, and cognitive decline. Surgical intervention offers the patient the best opportunity of seizure resolution, which occurs in approximately 50%–60% of patients, and improvement in both cognitive and behavioral difficulties. For those in whom the initial operation has failed, further medical treatment options remain quite limited, whereas, in some cases, a second surgery may improve seizure outcome. The authors retrospectively reviewed their surgical cases to document the success rate and complications of reoperations in patients with HHs.
Data were obtained from the HH epilepsy surgery database at the Barrow Neurological Institute between 2003 and 2010. Surgical treatment consisted of open and endoscopic procedures, as well as radiosurgery. Demographic details, seizure history, presurgical evaluation, and postoperative follow-up data were evaluated.
In the last 7 years, 21 (13%) of 157 patients underwent reoperation after an initial epilepsy operation. The initial surgical approach in the 21 patients included: endoscopic (8 patients [38%]), transcallosal (8 patients [38%]), orbitozygomatic (3 patients [14%]), and radiosurgery (2 patients [10%]). Of the 8 patients who initially underwent endoscopic resection, repeat procedures included: radiosurgery in 4 (50%), an orbitozygomatic approach in 2 (25%), repeat endoscopy in 1 (12.5%), and a transcallosal approach in 1 (12.5%). Repeat procedures after an initial transcallosal resection included: endoscopic resection in 2 (25%); radiosurgery in 1 (12%); an orbitozygomatic approach in 2 (25%), and repeat transcallosal surgery in 3 (38%). Predominant seizure types that recurred after the first surgery were gelastic seizures, complex partial seizures, and tonic-clonic seizures. Magnetic resonance imaging in all patients prior to reoperation demonstrated either residual HH and/or connection with the mammillary bodies. Review of patients with more than 6 months of follow-up since the last surgery showed greater than 90% reduction in seizures in 4 patients (19%) and by 50%–90% in 10 patients (48%). Two patients were seizure free, and in 5 patients (24%) there was no change in seizure frequency. Following reoperation, none of the patients had any worsened behavioral issues such as increased rage attacks or disruptive violent behavior. New postoperative complications after reoperation included hemiparesis, thalamic stroke (asymptomatic and symptomatic), hyperphagia, and panhypopituitarism.
Reoperation should be considered in selected patients with HH in whom initial epilepsy surgery fails because more than half the patients have significant reductions in seizure.
Sandipan Pati, Reena G Rastogi, Adib A. Abla, Harold L. Rekate, and Yu-Tze Ng
Gelastic seizures are epileptic events characterized by bouts of laughter. They are rare and mostly associated with hypothalamic hamartomas (HHs). Status gelasticus, a rare form of status epilepticus, is defined as a prolonged cluster of gelastic seizures (> 20–30 minutes) without necessarily involving loss of awareness between seizures. Emergency resection of the hamartoma is highly effective in these situations and should be considered as early as possible. The authors retrospectively reviewed their surgical cases to document the success, complications, and long-term follow-up after emergency resection of HHs for status gelasticus.
The authors report on a retrospective case series from a single tertiary care center. Three patients who presented with status gelasticus underwent emergency resection of HHs. Demographic details, seizure history, medical treatment, and postoperative follow-up data were evaluated. Long-term follow-up (minimum 2 years) data were obtained either from the last clinic visit notes or via telephone and e-mail contacts. The institutional review board at St. Joseph's Hospital approved this study.
In the last 7 years, of 157 patients who underwent HH resection, the resection was performed on an emergency basis for status gelasticus in 3 cases. At emergency surgery, these 3 patients ranged in age from 9 months to 3.5 years. All of the patients were boys. Delalande and Fohlen Type II, III, and IV lesions were present in the 3 patients. Surgical approaches for resection of HH included an orbitozygomatic, transcallosal anterior interforniceal approach and endoscopic resection. Status gelasticus was terminated following emergency surgery in all cases, and 1 patient was seizure free. Postsurgical complications included, in 1 case, a small right thalamic infarct with mild transient left hemiparesis, which completely resolved within 2 days. Within 2 years of their original surgery, 2 patients underwent further elective surgeries (endoscopic resection and radiosurgery for persistent symptomatic seizures). Follow-up since their most recent surgery ranged from 8 months to 2 years. Two patients were seizure free and 1 patient had greater than 50% reduction in seizures.
Status gelasticus associated with HHs can be successfully terminated by emergency resection of the HH. Long-term follow-up in the present series suggests good seizure freedom results or at least greater than 50% reduction in seizures, although repeat operations were necessary.
Adib A. Abla, Scott D. Wait, Jonathan A. Forbes, Sandipan Pati, Roger E. Johnsonbaugh, John F. Kerrigan, and Yu-Tze Ng
In this paper, the authors' goal was to describe the occurrence of alternating hypernatremia and hyponatremia in pediatric patients who underwent resection of hypothalamic hamartomas (HHs) for epilepsy. Hypernatremia in patients after pituitary or hypothalamic surgery can be caused by diabetes insipidus (DI), whereas hyponatremia can occur due to a syndrome of inappropriate antidiuretic hormone, cerebral salt wasting, or excessive administration of desmopressin (DDAVP). The triphasic response after surgery in the pituitary region can also explain variations in sodium parameters in such cases.
One hundred fifty-three patients with HH who underwent surgery were enrolled in a prospective study to monitor outcomes. Of these, 4 patients (2.6%) were noted to experience dramatic alterations in serum sodium values. The medical records of these patients were identified and evaluated.
Patients' ages at surgery ranged from 1.2 to 6.0 years. All patients were girls. Two patients had Delalande Type IV lesions (of 16 total Type IV lesions surgically treated) and 2 had Type III lesions (of 39 total Type III lesions). All patients had a history of gelastic seizures refractory to medication. Seizure frequency ranged from 3 to 300 per day. After surgery, all patients experienced hypernatremia and hyponatremia. The largest fluctuation in serum sodium concentration during hospitalization in a single patient was 53 mEq/L (range 123–176 mEq/L). The mean absolute difference in maximum and minimum sodium values was 38.2 mEq/L.
All patients exhibited an initial period of immediate DI (independent of treatment) after surgery followed by a period of hyponatremia (independent of treatment), with a minimum value occurring between postoperative Days 5 and 8. All patients then returned to a hypernatremic state of DI, and 3 patients still require DDAVP for DI management. A second occurrence of hyponatremia lasting several days without DDAVP administration occurred in 2 patients during their hospitalization between periods of hypernatremia. One patient stabilized in the normal range of sodium values prior to discharge from rehabilitation without the need for further intervention. At last follow-up, 3 patients are seizure-free.
Severe instability of sodium homeostasis with hypernatremia and hyponatremia is seen in up to 2.6% of children undergoing open resection of HH. This risk appears to be related to HH type, with a higher risk for Types III (2 [5.1%] of 39) and IV (2 [12.5%] of 16) lesions. Here, the authors describe alternating episodes of hypernatremia and hyponatremia in the postoperative period following HH surgery. Management of this entity requires careful serial assessment of volume status and urine concentration and will often require alternating salt replacement therapy with DDAVP administration.
Ganne Chaitanya, Andrew K. Romeo, Adeel Ilyas, Auriana Irannejad, Emilia Toth, Galal Elsayed, J. Nicole Bentley, Kristen O. Riley, and Sandipan Pati
Despite numerous imaging studies highlighting the importance of the thalamus in a patient’s surgical prognosis, human electrophysiological studies involving the limbic thalamic nuclei are limited. The objective of this study was to evaluate the safety and accuracy of robot-assisted stereotactic electrode placement in the limbic thalamic nuclei of patients with suspected temporal lobe epilepsy (TLE).
After providing informed consent, 24 adults with drug-resistant, suspected TLE undergoing evaluation with stereoelectroencephalography (SEEG) were enrolled in the prospective study. The trajectory of one electrode planned for clinical sampling of the operculoinsular cortex was modified to extend it to the thalamus, thereby preventing the need for additional electrode placement for research. The anterior nucleus of the thalamus (ANT) (n = 13) and the medial group of thalamic nuclei (MED) (n = 11), including the mediodorsal and centromedian nuclei, were targeted. The postimplantation CT scan was coregistered to the preoperative MR image, and Morel’s thalamic atlas was used to confirm the accuracy of implantation.
Ten (77%) of 13 patients in the ANT group and 10 (91%) of 11 patients in the MED group had electrodes accurately placed in the thalamic nuclei. None of the patients had a thalamic hemorrhage. However, trace asymptomatic hemorrhages at the cortical-level entry site were noted in 20.8% of patients, who did not require additional surgical intervention. SEEG data from all the patients were interpretable and analyzable. The trajectories for the ANT implant differed slightly from those of the MED group at the entry point—i.e., the precentral gyrus in the former and the postcentral gyrus in the latter.
Using judiciously planned robot-assisted SEEG, the authors demonstrate the safety of electrophysiological sampling from various thalamic nuclei for research recordings, presenting a technique that avoids implanting additional depth electrodes or compromising clinical care. With these results, we propose that if patients are fully informed of the risks involved, there are potential benefits of gaining mechanistic insights to seizure genesis, which may help to develop neuromodulation therapies.