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|Year : 2021 | Volume
| Issue : 6 | Page : 1813-1816
MRI-Negative Occipital Lobe Epilepsy Presenting as Gelastic Seizures
Lingli Hu, Fang Ding, Shan Wang, Shuang Wang
Department of Neurology, Epilepsy Center, Second Affiliated Hospital, School of Medicine, Zhejiang University, Hangzhou, Zhejiang, China
|Date of Submission||28-Jan-2019|
|Date of Decision||24-Jun-2019|
|Date of Acceptance||21-Jan-2020|
|Date of Web Publication||23-Dec-2021|
Dr. Shuang Wang
Department of Neurology, Epilepsy Center, Second Affiliated Hospital, School of Medicine, Zhejiang University, 88 Jiefang Rd., Hangzhou, Zhejiang, 310009
Source of Support: None, Conflict of Interest: None
Although gelastic seizures (GSs) with extrahypothalamic epileptogenic zones such as the frontal, temporal, or parietal lobes have been previously reported, reports of GSs arising from the occipital region are rare. Herein, we describe the seizure propagation pattern of mirthless GSs confirmed by intracranial EEG in a case of MRI-negative occipital lobe epilepsy. In this patient, EEG onset was localized to the right occipital lobe while the onset of laughter coincided with seizure propagation to the right basal temporal region. This finding suggested that the symptomatogenic area for GSs in the occipital lobe may reside in the basal temporal region, and the basal temporal region may play a role in laughing behaviors. This case demonstrated that an elaborate analysis of electroclinical features combined with imaging findings may lead to successful seizure localization.
Keywords: Basal temporal region, gelastic seizures, intracranial EEG, occipital lobe
Key Message: GSs arising from the occipital region are rare, the basal temporal region may play a role in laughing behavior.
|How to cite this article:|
Hu L, Ding F, Wang S, Wang S. MRI-Negative Occipital Lobe Epilepsy Presenting as Gelastic Seizures. Neurol India 2021;69:1813-6
Gelastic seizures (GSs) are a rare type of seizure characterized by unprovoked, stereotyped, uncontrollable laughter with or without mirth and are mainly observed in patients with hypothalamic hamartoma. GSs caused by cortical foci have been commonly reported in patients with frontal or temporal lobe epilepsy and occasionally occur in patients with posterior lobe epilepsy. However, GSs that originate from the focal occipital cortex are not well characterized. Herein, we describe the case of a boy with a subtle right occipital ganglioglioma presenting as GSs. Surgical resection guided by intracranial EEG (iEEG) evaluation rendered him seizure-free at a 3-year follow-up.
| » Case Presentation|| |
An 8-year-old right-handed boy began to have episodes of mirthless laugher lasting for about 10 s at the age of 6. His familial and personal history were uneventful, and his developmental milestones were normal. His school performance was excellent. The GSs were sometimes preceded by a vague and brief aura that he felt as several firing guns or jumping rabbits in his left front side. His consciousness was preserved during these episodes, and the boy stated that he experienced “funny” laughing without feelings of pleasure. The seizures initially occurred 2–3 times per day and became pharmacoresistant to antiepileptic drugs including oxcarbazepine and valproate. Although levetiracetam was added to his treatment regimen later, it caused mood instability. Scalp video-EEG monitoring was performed twice at 5 months apart. Both EEGs revealed a symmetric and normal posterior background (8–9 Hz), intermittent slowing in bilateral posterior quadrants (more prominent on the right side), and sharp waves in the right occipitotemporal region (O2, T6). Five subclinical seizures and four habitual clinical seizures were recorded during wakefulness, and ictal EEG changes were localized to the right occipitotemporal region. Electrical stimulations were performed to map functionally eloquent regions, no habitual seizures were induced by stimulation. Several routine brain MRI scans and one high-resolution MRI scan (epilepsy protocol) were performed, and the results from these scans were all normal. Brain positron emission tomography (PET) revealed focal hypometabolism in the right occipital lobe, and MRI post-processing suggested a suspicious lesion in the same area, which was consistent with the EEG findings [Figure 1].
|Figure 1: Imaging analysis. (a) Axial T1 MRI views showing “normal” cortical structure in the right occipital lobe, (b) FDG-PET images fused with MRI showing a focal hypometabolism in the right occipital lobe, (c). Voxel-based morphometry (VBM) analysis of 3D T1 image showing a suspicious lesion in the same area, (d) Postoperative MRI showing the extent of surgical resection, (e) Electrode reconstruction based on postimplantation CT and presurgical MRI showing the localization of EEG onset (red dots, lateral contacts of electrode G), their positions were in the vicinity of the suspicious lesion|
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Clinically, GSs have been rarely reported in patients with occipital lobe epilepsy. We hypothesized that these seizures may originate from the occipital region and propagate to the symptomatogenic zone in the frontal or temporal regions. Therefore, we performed an iEEG with electrodes that covered the right occipital region, occipitotemporal region, mesial temporal structures, temporal pole, and frontal regions. A total of 19 typical seizures were recorded during iEEG evaluation. Interictal spikes were located in the right occipital and basal temporal regions. Ictal EEG change was characterized by low-voltage, fast activity arising from the vicinity of the suspicious lesion in the right occipital cortex (Contacts G8–G11). Later, the discharge rapidly spread over the right occipitotemporal junction. Several seconds after the EEG onset, the right basal temporal region was involved in seizures, and the boy manifested laughing behavior. However, the frontal operculum and orbitofrontal lobe were not involved in seizures. We visualized the seizure propagation using epileptogenicity mapping (EM) [Figure 2] as described in David' study. The patient underwent a limited right occipital lobectomy, and histopathological analysis revealed the presence of a low-grade ganglioglioma (Grade, WHO I). The boy was seizure-free for 36 months and off antiepileptic medications for 24 months. No precocious puberty or cognitive impairment was observed after surgery.
|Figure 2: Intracranial EEG analysis. (a) IEEG recordings showing the onset of fast activity in contacts G8–G11 (red dots); the contacts F (lateral occipitotemporal gyrus) and E (basal temporal) belonged to the primary seizure propagation areas. Ictal activation of E2–E7 involvement was coincident with clinical onset of laugher, (b) Epileptogenicity maps of seizure propagation. Ictal EEG onset (0s) occurred at contacts G8–G11, 1 s later contacts F1–F3, F7–F9 and 2 s later contacts E2–E7 were involved. Numbers on color code indicate epileptogenicity index values|
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| » Discussion|| |
In the present study, we described the seizure propagation pattern of GSs in the case of MRI-negative occipital lobe epilepsy. The patient's complex visual aura could be explained by the activation of the visual cortex near the seizure onset zone., In addition, the iEEG evaluation showed that the onset of laugher coincided with seizure propagation to the basal temporal region. However, the frontal lobe was not involved in seizures; therefore, the basal temporal region may serve as the symptomatogenic zone of GSs.
GSs are most frequently observed in patients with hypothalamic hamartoma (HH) and focal cortical foci. When GSs originate in patients with HH, the neocortex generally becomes secondarily involved. However, the detailed dynamics of seizure propagation patterns have not yet been demonstrated, and only two related cases have been reported. Specifically, Kahane et al. used depth electrodes to document early propagation from the HH to the cingulate gyrus in three patients, and EEG/fMRI data demonstrated another pathway from the HH through the left fornix to the temporal lobe and later through the cingulate fasciculus to the left frontal lobe in one patient. GSs caused by cortical foci have been commonly reported in patients with frontal or temporal lobe epilepsy when GSs originate in patients with focal cortical foci, studies based on iEEG recordings and electrical cortical stimulation (ES) have revealed several symptomatogenic areas for laughter, including the superior frontal gyrus, cingulate gyrus, frontal operculum, supplementary motor area (SMA), orbitofrontal gyrus, and basal temporal cortex., However, GSs rarely originate in the occipital lobe, and the transmission pathway is still unclear. Conversely, the transmission pathway of occipital lobe epilepsy has been reported in the current literature and is based on the calcarine fissure. For example, medial occipital electric activity arising above the calcarine fissure usually propagates to the frontal lobe while medial occipital electric activity arising below the calcarine fissure propagates to the mesial temporal lobe. According to this theory, lateral occipital seizures will spread to the parietal and lateral temporal lobes. In the present case, electrical activity from the lateral occipital lobe spread to the temporal base, which is partially consistent with the pathway described in the previous literature.
To date, the pathways that are involved in the relationship between mirth and laughter have not been defined. According to Arroyo et al., laughter and mirth could be dissociated neurologically. The basal temporal cortex was involved in the processing of mirth whereas the anterior cingulate region was involved in the motor aspects of laughter. In a recent paper, the two cases with temporal lobe epilepsy underwent the implantation of a subdural electrode where laughter and mirth were elicited by the cortical stimulation of the left basal temporal cortex. However, other reports have demonstrated that stimulation of the anterior cingulate gyrus, supplementary sensorimotor area, frontal operculum, and superior frontal gyrus produce laughter with or without mirth. In the current study, the mirthless GSs occurred when the right basal temporal region was involved in the seizure. This finding suggests that the basal temporal region may play a role in the neuronal network of laughter, which likely involves laughing behavior and emotion. Therefore, the stimulation of any constituent unit of the neuronal network may completely or partly excite the network, and this excitation may result in GSs with or without mirth.
Findings from this case report and previously reported studies suggest that the GSs per se are a poorly localizing sign and they occur in epilepsy of cortical origin in every cerebral lobe,. Our results also demonstrated that the elaborate analysis of electroclinical features and imaging findings may lead to the successful localization of seizures and surgical outcomes in patients with epilepsy including MRI-negative cases with rare seizure types.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
This study was supported by the National Natural Science Foundation of China (81671282).
Financial support and sponsorship
This study was supported by the National Natural Science Foundation of China (81671282).
Conflicts of interest
The authors declare no conflict of interest.
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