Both cats and dogs suffer from seizures, however the diagnostic and treatment approach for cats differ greatly from their canine companions, and, at times, it can seem frustrating and challenging.
We can find many causes for Feline Epilepsy, from metabolic problems, toxins, or genetics. Therefore, a complete diagnostic approach is necessary to determine a diagnosis. A full history, physical and neurological examination are always crucial.
Different types of Epilepsy in cats:
Feline Idiopathic Epilepsy (or Epilepsy of Unknown Origin):
Feline Idiopathic Epilepsy (of unknown origin) is diagnosed in 22% of cats suffering seizures. Overall, cats can develop idiopathic epilepsy at any age (range 0.4 to 14 years), but median age is around 4.5 years old.
The diagnosis is made by exclusion, ruling out of other causes for seizures. MRI and CSF, along other diagnostic tests, are typically normal.
Feline Audiogenic Reflex Seizures (FARS)
Feline audiogenic reflex seizures is an important type of epilepsy in cats and is triggered by various high-pitched noises, usually causing a strong startle reflex called myoclonic seizures.
Cats suffering FARS usually present with myoclonic seizures, but generalised tonic-clonic seizures and absence seizures can also occur as part of this syndrome. Myoclonic seizures only last for a fraction of a second, and many cats will appear to remain conscious throughout. The seizure is characterised by brief involuntary muscle jerks or spasms, and this was the type of seizure seen in almost 95% of the FARS cats studied.
Hippocampal and piriform lobe lesions can be found on brain MRI and histopathology of some cats with a particular clinical presentation of seizures.
MR imaging abnormalities are restricted to the hippocampus and piriform lobe. The lesions are T2-hyperintense, T1-hypointense, and with various degrees of contrast enhancement.
Histopathologic findings in euthanised cats found severe, diffuse, bilateral symmetric necrosis, and degeneration of neurons in the hippocampus and piriform lobe, along with pronounced astrogliosis and mild lymphocytic inflammation.
Cerebrospinal fluid (CSF) analysis in some cases reveals elevated protein content and nucleated cell count with mixed pleocytosis. However, these findings are difficult to interpret as mixed pleocytosis in the CSF following seizures has been previously reported in dogs.
Feline Temporal Lobe Epilepsy:
Feline Orofacial Seizures (FEPSO) Linked to VGKC-Complex-Ab Limbic Encephalitis
This is a form of epilepsy related to hippocampal necrosis in cats. This presentation is also referred to as FEPSO. The features have some similarity to those described in humans with limbic encephalitis and voltage-gated potassium channel (VGKC) complex antibodies. Accumulating evidence suggests that these epileptic seizures originate from the temporal lobe (TL) in cats.
Pre-synaptic voltage-gated potassium channels (VGKC) in the brain have an inhibitory function over glutamate release. As glutamate is the main excitatory neurotransmitter, VGKC activity reduces seizure activity. These channels work along a family of proteins, especially leucine-rich glioma inactivated 1 (LGI1), that allow VGKC to be active.
VGKC-complex antibodies against LGI1 have been found in a cohort of cats (5/14) with seizures and MRI or histopathological signs of hippocampal necrosis, suggesting that an autoimmune process causes inactivation of LGI1 and VGKC, causing more glutamate release and therefore decreasing the seizure threshold. Follow-up sera were available for 5 cats in remission and all antibody concentrations were within the reference range. This study suggests that an autoimmune limbic encephalitis exists in cats and that VGKC-complex/LGI1 antibodies may play a role in this disorder, as they are thought to in humans.
Treatment is based on supportive treatment, immunosuppressive drugs such as corticosteroids along with phenobarbital and other AEDs (levetiracetam and diazepam). Resistance to treatment is common, although some reports describe good control when treatment was started early and aggressively, with some cats even achieving remission.
Hippocampal Necrosis and Temporal Lobe Epilepsy Linked to Brain Tumours
Contrary to previous reports of FHN in which no underlying cause could be identified, a case report of a cat with seizures consistent with FEPSO and signs of hippocampal necrosis on MRI, identified that 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.
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