Diagnosis

Seizures are often diagnosed based on the his­tory supplied by the owner rather than on the clinician witnessing the event. Because of this, it is important to ask appropriate questions to confirm that the episode was in fact a seizure and not something else.

Chronic Disease Managementfor Small Animals, First Edition. Edited by W. Dunbar Gram, Rowan J. Milner and Remo Lobetti.

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A history and general physical examina­tion are very important, followed by a neu­rologic examination. Though we generally treat all seizures the same way, it is of criti­cal importance to know what is causing the seizures, both for appropriate long-term treatment and accurate prognosis. We must first determine if seizures are due to extra-cranial or intra-cranial disease. This is where the minimum database is crucial: a complete blood count, serum chemistry profile and urinalysis can reveal many abnormalities. A blood pressure measure­ment, a thyroid measurement in cats, and thoracic radiographs are also helpful in many cases. Animals with extra-cranial causes of seizures do not often require anti-seizure medications once the underly­ing disease is treated. Major systemic abnormalities to consider include hypogly­cemia, hypocalcemia, and hepatopathies, including portosystemic shunts. Common intracranial causes of seizures include idi­opathic processes, inflammatory diseases, neoplasia, and malformations. Less com­mon causes include infectious diseases, vascular events, and inborn errors of metabolism.

Animals with genetic or unknown (idio­pathic) epilepsy, by definition, will have a normal neurologic examination between sei­zures.

Approximately 80% of dogs over 7 years of age with a new onset of seizures will have a structural reason; the remaining 20% will be cryptogenic epilepsy (having a late-onset sei­zure disorder with a grossly structurally nor­mal brain). Many dogs with a structural intracranial lesion will have a normal neuro­logic examination because there are silent areas in the brain.

Cats are a bit different. In domestic felines, symptomatic epilepsy is most common, accounting for 40-50% of seizure cases. Presumptive idiopathic and reactive epilepsies are about tied for the second and third causes of seizures, between 25% and 50% each. Cardiac syncope comes in as the fourth most common cause of “seizures,” though these are truly cats with severe arrhythmias, such as a third-degree AV block or sick sinus syndrome. In cats, focal and generalized seizures appear with even fre­quency. A generalized seizure in a cat will be similar to that of a dog; there will be ptyalism, tonic-clonic muscular activity, urination, defecation, but cats may vocalize during the seizure. Cats can also have seizure episodes with minimal overt motor activity; there may be twitching of part of the face and ptyalism, but a key finding in these cases is hyperther­mia. Epilepsy of unknown cause in cats has a higher survival rate than in dogs with an approximately 45% remission rate. Basically, we do see epileptic cats, and they tend to do much better than dogs.

Differential diagnosis lists for intracranial causes of seizures will vary based on age and breed, but the following list is a guide:

• < 1 year: Metabolic (hypoglycemia),

Congenital (hydrocephalus), Infectious

• 1-5 years: Genetic/Idiopathic, Inflammatory,

Neoplastic

• >6 years: Neoplastic, Inflammatory,

Cryptogenic

• Geriatric: Neoplastic, Vascular, Cryptogenic Breed should also be considered when think­ing about seizures. A young, large-breed dog is most likely to have a genetic or unknown epilepsy while a young to adult terrier or toy­breed dog is more likely to have an inflamma­tory meningoencephalitis. A middle-aged brachycephalic breed with a new onset of seizures should raise concern for intracranial neoplasia - a glial tumor in particular. Geriatric large-breed dolichocephalic dogs, in contrast, are at higher risk of meningiomas.

Box 8.1

Common intracranial etiologies of seizures Age first seizure noted: Common Causes 6 years: Neoplastic, Inflammatory, Cryptogenic

Geriatric: Neoplastic, Vascular, Cryptogenic