WSAVA Nov 2021 Proceedings - Flipbook - Page 30
13–1 5 NOVEMBER, 202 1
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WHAT IS SO SPECIAL ABOUT FELINE EPILEPSY?
L. Garosi
IPER/United Kingdom
Qualifications:
Dr Laurent Garosi DVM, Dip ECVN, FRCVS
RCVS & EBVS® European Specialist in Veterinary Neurology
Laurent.garosi@vetoracle.com
RECOGNITION OF AN EPILEPTIC SEIZURE
Seizure types can be classified into two major categories: partial and
generalised. Compared to dogs, cats commonly exhibit partial seizures.
The focal nature of this seizure type is associated with a higher incidence of focal intracranial pathologic change in cats. These can be focal
(partial motor or more often partial complex seizure) seizures: unaltered
consciousness with asymmetric localised motor signs such as eyelid or
facial twitching, clonus of muscle groups of one limb – or psychomotor
(complex partial) seizures: behavioural seizures pattern involving the limbic system which may be seen as growling, vocalization, rage, aggression
without provocation, running in circles, floor licking, tail chasing… Compared to dogs, cats tend to experience high seizure frequency whatever
the underlying cause.
The recognition of an epileptic seizure is essentially based on the owners’
description of the event. Apart for the unequivocal description of a generalised tonico-clonic seizure, the recognition of a partial or psychomotor
seizure can be a real challenge for the clinician. Video footage obtained
by the owner can be for that particular reason of precious help. An epileptic seizure can be suspected based on the peracute and unexpected (except cases of “reflex seizures” where seizures are observed in response
to specific stimuli such as auditory reflex seizures which we are currently
investigating) onset and offset, stereotypical pattern (i.e. each seizures
are fairly similar in following the same pattern), presence of involuntary
motor activity and/or abnormal mentation and behaviour and/or autonomic signs (salivation, urination and/or defecation), and elimination of other
paroxystic events (syncope, acute vestibular attack, myasthenia gravis).
CLINICAL EVALUATION OF A CAT WITH SEIZURES
An epileptic seizure is not a disease entity in itself but a clinical sign generally indicative of a forebrain disorder. Neurological examination should
therefore focus on detecting forebrain signs (evaluation of mental status,
presence of circling gait, postural reaction testing, assessment of menace
response and response to nasal stimulation).
The detection of forebrain signs on neurological evaluation in the inter-ictal period rules-out as a general rule the hypothesis of primary epilepsy.
The only exceptions to this rule are ischaemic necrotic brain lesions
secondary to violent seizures (excitotoxicity phenomenon). Such lesions
are particularly found in cats in the NMDA receptor-rich brain region such
as the hippocampus. Inter-ictal neurological deficits frequently observed
include mainly behavioural changes (aggression, fear, hyperexcitability,
uncontrolled biting, chasing…).
GENERATING A LIST OF DIFFERENTIALS
Seizures refer to a forebrain disorder. Their causes may originate outside
(extra-cranial) or inside (intra-cranial) the brain.
Causes of seizures found outside the brain (extra-cranial) may be found
outside the body (toxic disorder) or inside the body (metabolic disorder).
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WSAVA GLOBAL COMMUNITY CONGRESS
In both instances, the cat may have normal or abnormal neurological examination in the interictal period. If neurological signs are seen, they are
typically symmetrical and non-localising in term of anatomic diagnosis.
Common metabolic causes include hepatic encephalopathy (either due to
portosystemic shunt or to cirrhosis), renal encephalopathy, ionic imbalance (hypocalcemia, hyponatremia, hypernatremia, hypomagnesemia or
hyperkaliemia), hypoglycaemia, polycythemia, and hyperthyroidism. Common toxic or nutritional disorder seen in cats include lead, ethylene glycol,
organophosphate and methaldehyde poisoning and thiamine deficiency.
Intracranial causes of epileptic seizures can further be divided into functional and structural forebrain disorder. Most cats with structural forebrain
disorder show neurological signs in the interictal period. These signs are
often asymmetric and can localise the lesion. They can refer to a forebrain
disorder (ipsilateral circling, contralateral postural reaction deficit, contralateral menace response loss with normal pupillary light reflex, contralateral abnormal response to stimulation of the nostril, abnormal behaviour)
or to a multifocal disorder (cranial nerve or spinal cord involvement). The
exception to this is a structural lesion in a “silent area” of the brain (region
of the brain which causes only seizures with no other localising signs
such as the olfactory lobe or prefrontal lobes) or in the early stage of an
enlarging (and eventually slowly growing) mass. Structural brain diseases include: cerebrovascular accident (common known causes in cats
include cardiomyopathy, glomerulopathy, hyperthyroidism, intoxication by
anti-coagulant and parasitism), infectious encephalitis (Feline Infectious
Peritonitis, FIV, FeLV-associated CNS lymphoma, Toxoplasmosis, Borna
disease and bacterial meningo-encephalitis), immune-mediated encephalitis, post-head trauma, primary and metastatic brain tumour, and anomalous (hydrocephalus).
A syndrome of complex partial seizures with orofacial automatism (FEPSO) has been described in cats who will display signs of salivation, facial
twitching, chewing, growling, rapid turning… This syndrome has been
associated with hippocampal pathology. In human, similar syndrome is
seen with autoimmune limbic encephalitis and is associated with antibody
against VGKC (voltage-gated potassium channel complex). Similar pathology has been documented in cats and it is also suspected VGKC complex
antibody may play an important role in naturally occurring seizure disease
in this species. Brain MRI showed bilateral hippocampal T1 hypo- and
isointensity and T2 hyperintensity.
Feline reflex auditory seizure (FARS) is also a newly recognised form of
epilepsy in cats. It appears to be more common in older cats and Birmans,
and is triggered by various high-pitched noises. Myoclonic seizures were
one of the cardinal signs of this syndrome in almost all cats, frequently
occurring prior to generalised tonic–clonic seizures (GTCSs). Other
features include a late onset (median 15 years) and absence seizures in
a small number of cats, with most seizures triggered by high-frequency
sounds amid occasional spontaneous seizures (up to 20%). Half the population had hearing impairment or were deaf. One-third of cats in one of our
study had concurrent diseases, most likely reflecting the age distribution.
Birmans appear to be predisposed. Aside for avoiding the stimulus if
possible, levetiracetam gave good seizure control and is more effective
than phenobarbital.
The term primary (or idiopathic) epilepsy implies a functional forebrain
disorder causing recurrent epileptic seizures with a normal interictal period and no identifiable toxic, metabolic or structural intracranial causes.
This type of epilepsy is considered less common in cats as compared to
dogs and is a diagnosis of exclusion.
CHOOSING THE APPROPRIATE DIAGNOSTIC WORK-UP
Baseline blood work including a complete blood count, chemistry profile,
thyroid profile, bile acids, blood pressure as well as a urinalysis should be
performed in all cats with seizures to rule-out metabolic causes.
Dog with idiopathic epilepsy typically begin to seizure between 1 and 5