Temporal lobe epilepsy in cats.

In recent years there has been increased attention to the proposed entity of feline temporal lobe epilepsy (TLE). Epileptic discharges in certain parts of the temporal lobe elicit very similar semiology, which justifies grouping these epilepsies under one name. Furthermore, feline TLE patients tend to have histopathological changes within the temporal lobe, usually in the hippocampus. The initial aetiology is likely to be different but may result in hippocampal necrosis and later hippocampal sclerosis. The aim of this article was not only to summarise the clinical features and the possible aetiology, but also being work to place TLE within the veterinary epilepsy classification. Epilepsies in cats, similar to dogs, are classified based on the aetiology into idiopathic epilepsy, structural epilepsy and unknown cause. TLE seems to be outside of this classification, as it is not an aetiologic category, but a syndrome, associated with a topographic affiliation to a certain anatomical brain structure. Magnetic resonance imaging, histopathologic aspects and current medical therapeutic considerations will be summarised, and emerging surgical options are discussed.

A case of feline temporal lobe epilepsy with hippocampal sclerosis and dentate gyrus malformation.

A two-months-old, male, mixed breed cat presented with epileptic seizures. The cat was diagnosed with drug-resistant epilepsy, and died at 3-years of age. No gross lesion was found at necropsy. Histopathologically, the dentate gyrus granule cell layer of the hippocampus was irregularly arranged. Granule cells were dispersed and ectopic cells were sporadically observed in the molecular layer. The granule cells had an enlarged cytoplasm and swollen nucleus. Immunohistochemistry for NeuN and GFAP confirmed severe neuronal loss and mild gliosis in CA1. Binucleation and ischemic change were observed in the remaining pyramidal cells. This report describes a case of feline temporal lobe epilepsy and hippocampal sclerosis associated with dentate gyrus malformation.

Feline temporal lobe epilepsy: seven cases of hippocampal and piriform lobe necrosis in England and literature review.

CASE SERIES SUMMARY: Seven cases of feline hippocampal and piriform lobe necrosis (FHN) are described, with particular emphasis on clinical, radiographic and histopathological correlations. FHN is an uncommon acute epileptic condition resembling human autoimmune limbic encephalitis and temporal lobe epilepsy. Seizures are typically focal and feature uni- or bilateral orofacial or head twitching, hypersalivation, lip smacking, mydriasis, vocalisation and motionless staring, with inter-ictal behavioural changes such as unprovoked aggression and rapid running. Emerging evidence supports an autoimmune aetiology, although disruption of hippocampal architecture secondary to brain neoplasia has also been recognised. Most commonly, however, the underlying cause remains unknown. Diagnosis is achieved clinically and with brain MRI; electroencephalography and voltage-gated potassium channel-complex autoantibodies are currently the subject of research. Affected cats are frequently refractory to conventional antiepileptic treatment. RELEVANCE AND NOVEL INFORMATION: Following a review of the literature, including potential complicating factors and comparisons with human medicine, the hippocampus and piriform lobe are proposed as the neuroanatomical localisation for focal seizures with orofacial involvement in cats, regardless of aetiology.

Ventrolateral temporal lobectomy in normal dogs as a counterpart to human anterior temporal lobectomy: a preliminary study on the surgical procedure and complications.

Anterior temporal lobectomy (ATL) is a surgical procedure for drug-resistant mesial temporal lobe epilepsy that is commonly performed in human medicine. The purpose of this study was to determine whether ATL-like surgery, i.e., removal of the amygdala and hippocampal head, is possible in dogs, and to investigate its safety and postoperative complications. Eight healthy beagles underwent ATL-like surgery and were observed for 3 months postoperatively. Samples from the surgically resected tissues and postmortem brain were evaluated pathologically. The surgical survival rate was 62.5%. The major postoperative complications were visual impairment, temporal muscle atrophy on the operative side, and a postoperative acute symptomatic seizure. Due to the anatomical differences between dogs and humans, the surgically resected area to approach the medial temporal structures in dogs was the ventrolateral part of the temporal lobe. Therefore, the ATL-like surgery described in this study was named "ventrolateral temporal lobectomy" (VTL). This study is the first report of temporal lobectomy including amygdalohippocampectomy in veterinary medicine and demonstrates its feasibility. Although it requires some degree of skill, VTL could be a treatment option for canine drug-resistant epilepsy and lesions in the mesial temporal lobe.

Comparison of electroencephalographic findings with hippocampal magnetic resonance imaging volumetry in dogs with idiopathic epilepsy.

BACKGROUND: In humans, temporal lobe epilepsy (TLE), is a type of focal epilepsy occurring mainly in the mesial TLE (mTLE), commonly associated with hippocampal sclerosis (HS). OBJECTIVES: According to recent studies, TLE might also occur in dogs and could be associated with hippocampal atrophy (HA)/HS. To date, hippocampal lesions have not been correlated with electroencephalographic (EEG) findings in epileptic dogs. ANIMALS: An EEG examination, brain magnetic resonance imaging, and volumetric assessment of the hippocampus were performed in 16 nonepileptic and 41 epileptic dogs. METHODS: In this retrospective study, the presence and localization of EEG-defined epileptiform discharges (EDs) was blindly evaluated. The hippocampus was measured and assessed for unilateral atrophy. The results of EEG and volumetric findings were correlated to determine whether the functional epileptic focus is equivalent to structural changes. RESULTS: The median hippocampal asymmetric ratio (AR) in epileptic dogs was significantly greater than in the control group (P < .001). Using a cut-off threshold AR of >6%, 56% (23/41) of the dogs were characterized with unilateral HA. Of those animals, 35% (8/23) had EDs in the temporal leads and 26% (6/23) had no EDs. In 88% (7/8) of dogs with EDs in the temporal leads that had unilateral HA, the EDs correlated with the side of the decreased hippocampal volume. CONCLUSIONS AND CLINICAL IMPORTANCE: The results indicate an association between the presence of EDs detectable on EEG and a decrease in the unilateral hippocampal volume in some cases of canine idiopathic epilepsy that might reflect features of human mTLE.

Bilateral preictal signature of phase-amplitude coupling in canine epilepsy.

Seizure forecasting would improve the quality of life of patients with refractory epilepsy. Although early findings were optimistic, no single feature has been found capable of individually characterizing brain dynamics during transition to seizure. Cross-frequency phase amplitude coupling has been recently proposed as a precursor of seizure activity. This work evaluates the existence of a statistically significant difference in mean phase amplitude coupling distribution between the preictal and interictal states of seizures in dogs with bilaterally implanted intracranial electrodes. Results show a statistically significant change (p<0.05) of phase amplitude coupling during the preictal phase. This change is correlated with the position of implanted electrodes and is more significant within high-gamma frequency bands. These findings highlight the potential benefit of bilateral iEEG analysis and the feasibility of seizure forecasting based on slow modulation of high frequency amplitude.

Feline Temporal Lobe Epilepsy: Review of the Experimental Literature.

Accumulating evidence suggests that epileptic seizures originating from the temporal lobe (TL) occur in cats. Typically, affected animals have clinically focal seizures with orofacial automatisms including salivation, facial twitching, lip smacking, chewing, licking, and swallowing. Motor arrest and autonomic and behavioral signs also may occur. Many affected cats have magnetic resonance imaging (MRI) changes within the hippocampus or histopathologically confirmed hippocampal sclerosis or necrosis. From the 1950s to the 1980s, cats frequently were used as animal models for neurophysiological experiments and electrophysiological studies, from which important basic knowledge about epilepsy originated, but which has been rarely cited in clinical veterinary studies. These studies were reviewed. Experimental research on cats showed the widespread anatomical connections among TL structures. The ictal clinical signs originating from the hippocampus, amygdala, or lateral temporal cortex are similar, because of their dense interconnections. The ictal signs can be divided into autonomic, somatic, and behavioral. For research purposes, a 6-stage system was established, reflecting the usual sequential progression from focal to generalized seizure: attention response (1), arrest (2), salivation, licking (3), facial twitching (4), head turning or nodding (5), and generalized clonic convulsions (6). Knowledge of this data may help in recognizing low-stage (stage 1 or stage 2) epileptic seizures in clinical practice. Early experimental research data are in accordance with recent clinical observations regarding ictal clinical signs of TL epileptic seizures in cats. Furthermore, the research data supports the idea that TL epilepsy represents a unique clinical entity with a specific seizure type and origin in cats.

Novel approach to temporal lobectomy for removal of a cavernous hemangioma in a dog.

OBJECTIVE: To report temporal lobe surgery for a cavernous hemangioma in a dog and outcome. STUDY DESIGN: Clinical report. ANIMALS: Dog (n = 1). METHODS: Magnetic resonance (MR) imaging was used to identify a temporal lobe mass in 9-year-old, male neutered Labrador Retriever that had a 12 hour history of seizures. An approach to the temporal lobe allowed preservation of the zygomatic arch and mass removal. RESULTS: The mass was confirmed as a cavernous hemangioma on histopathology. Repeat MR imaging at 13 months showed no recurrence of gross structural disease; however, the dog's anti-epileptic medication was administered for adequate seizure control. CONCLUSION: Temporal lobe surgery can be performed in the dog's for the management of temporal lobe mass lesions.

Temporal lobe epilepsy in a cat with a pyriform lobe oligodendroglioma and hippocampal necrosis.

A 14-year-old male domestic shorthair cat presented with an acute onset of aggressive behaviour, fear and hypersalivation. Neurological examination revealed bilateral mydriasis and left-sided facial twitching and hemiparesis. Magnetic resonance imaging (MRI) showed moderate bilateral symmetrical T2-hyperintensity along the entire hippocampus and bilateral asymmetric T2-hyperintensity in the pyriform lobes. Marked bilateral contrast enhancement of the hippocampus was evident on post-contrast T1-weighted images. The partial complex seizures were refractory to medical treatment and the cat was euthanased 4 days after admission. The clinical and MRI findings were consistent with feline hippocampal necrosis (FHN). On histopathology, neuronal necrosis and astrocytosis were present in the hippocampi and pyriform lobes. In addition, an oligodendroglioma was detected in the right pyriform lobe. Contrary to previous reports of FHN in which no underlying cause could be identified, we believe that in this case the seizure focus arose from a neoplastic lesion within the right pyriform lobe. This unique case report represents the so-called 'dual pathology' of temporal lobe epilepsy in humans, in which an extrahippocampal lesion within the temporal lobe results in hippocampal sclerosis.

Absence of temporal lobe epilepsy pathology in dogs with medically intractable epilepsy.

Epilepsy is a common neurological problem in dogs. In some dogs, seizures cannot be controlled adequately with anticonvulsant medication. Temporal lobe epilepsy is the most common type of epilepsy in adult humans, it is frequently resistant to anticonvulsant therapy, and it is commonly associated with characteristic neuropathological abnormalities in the hippocampal dentate gyrus. We sought to test the hypothesis that dogs with medically intractable epilepsy have temporal lobe epilepsy. The hippocampi of 6 dogs that were euthanized because of chronic, recurrent seizures were compared with those of 8 nonepileptic controls. In control and epileptic dogs, stereological cell counting showed similar numbers of neurons in the hilus of the dentate gyrus, somatostatin immunoreactivity identified numerous immunopositive neurons in the hilus, and Timm staining showed the normal pattern of granule cell axon projections. These findings demonstrate a lack of hilar neuron loss and granule cell axon reorganization, suggesting that temporal lobe epilepsy is not a common cause of medically intractable epilepsy in dogs.

Tail chasing in a bull terrier.

A Bull Terrier that was continuously chasing its tail was examined clinically, electroencephalographically, and by computed tomography of the head. The dog was also given test treatments with an anticonvulsant (diazepam) and a pure opioid antagonist (naloxone). The dog appeared to be hysterical and dissociated from its surroundings. Electroencephalography revealed a seizure pattern that was most marked over the temporal lobe, and computed tomography revealed mild hydrocephalus. Diazepam effectively controlled tail chasing, whereas naloxone did not. The dog was discharged on anticonvulsant therapy but subsequently had to be euthanatized when aggression developed. Results of examination and treatment have led the investigators to propose a hereditary mechanism for tail chasing, perhaps related to zinc malabsorption.

Phenobarbital-responsive episodic dyscontrol (rage) in dogs.

Episodic dyscontrol (rage) was diagnosed from the clinical history, electroencephalographic findings, and response to oral treatment with phenobarbital in 3 dogs. Clinical features included a mood change heralding aggressive incidents, explosive aggression directed at people or objects, and a postaggressive phase characterized by lethargy and lack of responsiveness. Abnormal electroencephalographic findings included spike activity in the temporal recordings. All 3 dogs responded well to anticonvulsant medication with phenobarbital.

Successful long term treatment of a dog with psychomotor seizures using carbamazepine.

Psychomotor seizures (temporal lobe epilepsy) were diagnosed in a dog based on history, clinical findings and electroencephalography. Long-term seizure control was achieved with carbamazepine, despite serum drug concentrations which were low to unmeasurable. It is suggested that serum levels of carbamazepine are not a useful guide to clinical efficacy in the dog, that an unmeasured metabolite of carbamazepine may account for the anti-convulsant activity and that carbamazepine may be potentially useful in treating certain canine seizure disorders.