The Diagnostic and Therapeutic Approach to Recurrent Seizures in the Cat
World Small Animal Veterinary Association World Congress Proceedings, 2004
Joane Parent, DMV, MVetSc, ACVIM (Neurology)
Ontario Veterinary College

The symptomatology, causes, diagnostic approach and treatment of seizures in the cat have little comparable to that of the dog. Seizure always originates from the thalamocortex. The thinking process, when presented with a cat with seizure activity, should start at that level. The abnormalities, structural or functional, are within this part of the brain. Not all areas of the brain have the same propensity to seize; from the most highly prone to seize to the least, we list the temporal, frontal, parietal and occipital lobes. Not all regions of the brain lead to a kindling effect either.

The most frequent types of seizures in the cat are the focal (complex partial) seizures, with or without secondary generalization. These seizures are often violent, the animal propelling itself in the air, biting his tongue, avulsing his claws, etc. Many cats however have seizure activity that goes unrecognized by owners and veterinarians. There is repetitive ear, eyelid or whisker fluttering and twitching. Symptomatic ("the epileptic seizures are the result of one or more identifiable structural lesions of the brain" ILEA) and likely symptomatic ("the epilepsy is believed to likely be symptomatic but no etiology has been identified" ILEA) epilepsies are the only epilepsies that we have diagnosed in the cat.

Causes of seizures

Most seizures in the cat are intracranial in origin. Rare are the seizures resulting from toxicities or metabolic diseases. In a study of cats with seizures, polycythemia was the only metabolic disease reported as a cause of seizures in this species but the cause of seizures in these cats was not the metabolic effect of the disease per se, but the vascular events that resulted from the hyperviscosity. The most common causes of seizures identified in the cat are:

1.  Viral non-FIP encephalitis

2.  Feline cerebral ischemic encephalopathy

3.  Neoplasia (meningioma commonly)

4.  Others

The viral non-feline infectious peritonitis (FIP) encephalitides are common causes of seizures in the young to middle-aged cat. The seizures may be preceded by unspecific transient systemic signs such as fever, anorexia, coughing, vomiting, diarrhea, up to three weeks prior to the onset of the seizures. Since, the animal has been normal. The seizure onset is acute and frequently progresses rapidly. The disease is often self-limited but the resulting lesion may be highly epileptogenic in reason of its location, with frequent partial and/or generalized seizures occurring as clusters and status epilepticus. On the database, there is often a marked increase in creatine kinase due to the constant muscle tremors/shaking these cats experience. Seizure control can be difficult but treatment is worthwhile as most cats with adequate care recover fully. Dexamethasone at 0.25 mg/kg q24h is given intravenously for 48 hours if the animal is presented in focal or convulsive status epilepticus. The cats usually require antiepileptic treatment for extended periods of time. As a rule, a minimum of six-month seizure-free time should elapse before gradually weaning the patient off medication.

Feline infectious peritonitis is likely if the cat is less than three years of age, has a protracted history, systemic signs and neurological disease. Central nervous system cryptococcosis has similar presentation but is observed in a wider range of age. These diseases are rare compared to the viral non-FIP encephalitides

The cat that becomes epileptic following an ischemic event may have infrequent seizures that may or not necessitate antiepileptic treatment. The outcome is good if the animal survives the initial cerebral ischemia. A few cats never display signs characteristic of feline cerebral ischemia. On these cats, the presumptive diagnosis is made on the magnetic resonance imaging (MRI) scan of the brain demonstrating bilateral but asymmetrical atrophy of the cerebrum. Brain tumors, especially meningiomas, are frequent causes of seizures in the cat > 10 years of age. In all, there is a behavioral component that often goes unnoticed by veterinarians and misinterpreted by owners as "old age". Meningiomas are relatively easy to remove surgically. Recurrences are frequent especially if the removal was not complete.

Young cats (6-10 months) that develop recurrent seizures and in which the neurological examination and ancillary tests are unremarkable often become intractable. It is important to have an adequate seizure control early to improve the outcome.

Diagnostic work up

1.  History taking

2.  Pattern of seizures (age at onset, breed, type and frequency of seizures)

3.  Physical and neurological examinations

4.  Ophthalmologic examination (fundus)

5.  CBC, chemistry and urinalysis

6.  +/- CSF analysis

7.  +/- MRI scan of the brain

8.  Titres (FeLV, FIV, Toxo)

The owner must be questioned on the animal's behavior in its home environment with details. It is only in cats severely demented that behavioral abnormalities are evident in the examining room. The following tests of the neurological examination target specifically the cerebral cortex and must be performed with attention to subtleties:

1.  Mental status

2.  Menace response

3.  Response to nasal septum stimulation

4.  Proprioceptive positioning (knuckling) or placing lateral tactile.

The funduscopic examination is often abnormal in the cat but findings rarely related to the cause of the seizures. What is important is to evaluate for presence of active lesions.

The infectious inflammatory diseases are generally systemic diseases even if the neurological signs predominate. There may be neutrophilia, hyperglobulinemia, increased hepatic enzymes, etc. It is important to recognize the abnormalities that are secondary to and not the cause of the epilepsy. As an example, creatine kinase (CK) is often significantly increased following clusters of seizures or status epilepticus, even if partial (non-convulsive).

The CSF analysis should always be performed if the seizure onset is acute and severe. This clinical presentation is unfortunately frequent in the cat less than 10 years of age. It is important to differentiate FIP encephalitis from non-FIP encephalitis. The latter carries a good prognosis. In FIP cases, there is marked pleocytosis and/or increase in protein concentration, which is not observed with viral non-FIP cases.

In chronic cases, the MRI scan of the brain is preferred. In these cases, the CSF analysis is often unspecific or the results within reference range.

Feline leukaemia virus (FeLV), feline immunodeficiency virus (FIV) and toxoplasmosis are rare causes of central nervous system diseases, seizures or not.

Antiepileptic drugs (AED)

1.  Phenobarbital

2.  Gabapentin

3.  Diazepam

4.  Potassium bromide (KBr)

Phenobarbital

Phenobarbital has a strong antiepileptic effect for focal (partial) and generalized seizures. The pharmacokinetics have been published for the cat. The optimal therapeutic range is 100-130 umol/L. It is difficult to titrate the oral dose due to significant daily variations without alteration of the oral dose. The recommended dosage is 7.5-15 mg per cat, twice daily. We initiate treatment at once per day and gradually increase to twice daily treatment to avoid (unavoidable) sedation. Phenobarbital is our AED of choice. Serum level measurements are readily available in commercial laboratories, the side effects are minimal (initial sedation, no hepatotoxicity reported), the cost is low and small size tablets exist. A Phenobarbital-related coagulopathy has been reported 30 years ago. There has been no mention since. None of our cats developed it. Until more is published on the treatment of seizures in cats, monitoring by way of regular CBC, chemistry and serum levels is advocated in all cats maintained on AED treatment.

Gabapentin

Gabapentin has been used in the young severe epileptic cat with some success. Initial sedation was observed when added to Phenobarbital but no other adverse effects were noted. The recommended dose is 10 to 40 mg q8h.

Diazepam

Diazepam has been our second line AED for two decades. It is gradually replaced by gabapentin in the animal refractory to phenobarbital. Diazepam is reported to be an efficient AED in the cat but no comparative study has been done to ascertain this statement. In vitro, diazepam is superior to phenobarbital in the treatment of focal (partial) seizures but the pharmacokinetics are unknown for the species, the measurement of the serum levels available only at institutions and special laboratories, and finally, although rare, acute life-threatening hepatic necrosis has been reported. One to 5 mg once to twice daily is advocated. Increase the dose very gradually to avoid sedation. A blood work should be done within the first 24 hours of treatment to evaluate for liver necrosis.

Potassium Bromide (KBr)

Potassium bromide frequently causes eosinophilic pulmonary infiltrates that may lead to acute death. In our pharmacokinetic study of KBr in the cat, 4 of the 6 experimental cats had eosinophilic pulmonary infiltrates at necropsy performed 18 weeks following arrest of the KBr treatment. On a study of 26 cats treated with KBr, 11 cats developed lower airway disease 7 weeks to 14 months following onset of treatment. Two cats died. Although the clinical signs resolve with the arrest of treatment (up to 17 months for full recovery), the disease is protracted. The safety of potassium bromide in the cat remains a serious issue. Our opinion is that it should not be used in the cat. If chosen, it should be used with extreme caution. Regular monitoring (every other month) of the lungs by way of thoracic radiographs would be imperative.

Prognosis

As a rule, the prognosis for arrest or control of the seizures is good. Contrary to the dog, the severity of seizures at onset is not an indicator of outcome. A grave or reserved prognosis should not be given when a cat is presented with an acute and severe onset of seizures. As in dogs, the prognosis for adequate seizure control in cats that start to seize prior to 10 months of age (with normal data base) is guarded. The convulsive seizures in these cats are often refractory to treatment, even with polypharmacy. The cause of the seizures in this age bracket is unknown but possibly relate to a microscopic congenital malformation/anomaly or perinatal anoxia. The MRI findings have been negative. It is important to institute treatment early. The goal of treatment in these patients is no seizure at all.

Conclusion

In most epileptic cats, the epilepsy is symptomatic or likely symptomatic in origin, but rarely genetic or idiopathic. With a thorough diagnostic work up, a definitive diagnosis can often be reached. The prognosis is not necessarily guarded even in the presence of frequent and severe seizures.

We invite you to visit www.neuroexamination.com for instructions on how to obtain the "The Canine and Feline Neurological Examination CD ROM".

Speaker Information
(click the speaker's name to view other papers and abstracts submitted by this speaker)

Joane Parent, DMV, MVetSc, ACVIM (Neurology)
Ontario Veterinary College


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