Page 1123 - Small Animal Internal Medicine, 6th Edition

CHAPTER 62 Seizures and Other Paroxysmal Events 1095

BOX 62.2 IE has always been considered to be uncommon in cats, but
most recent reports suggest that 20% to 50% of cats with
VetBooks.ir Common Disorders Resulting in Seizures recurrent seizures may have IE. Intracranial causes of sei-
zures are, however, much more common in cats than in dogs,
Extracranial Causes (Reactive Seizures)
Toxins so an intracranial evaluation is still recommended in all cats
with recurrent seizures.
Metabolic diseases A genetic basis for IE is strongly suspected or proven in
Hypoglycemia German Shepherd dogs, Belgian Tervurens, Keeshonds,
Liver disease Beagles, Dachshunds, Labrador Retrievers, Golden Retriev-
Hypocalcemia ers, Poodles, Border Collies, Shetland Sheepdogs, Irish
Hyperlipoproteinemia
Hyperviscosity Wolfhounds, Vizslas, Bernese Mountain Dogs, and English
Hypertension Springer Spaniels. Genetic factors are likely in other affected
Electrolyte disturbances breeds as well, and IE is often called familial epilepsy.
Hyperosmolality The first observed seizure in dogs with IE usually occurs
Severe uremia between 6 months and 3 years of age, although seizures are
Hyperthyroidism (cats) not observed until 5 years of age or older in some dogs. In
Hypothyroidism (dogs)—predisposition to intracranial most breeds it seems that the younger the age at the onset of
infarcts a seizure disorder, the more difficult the disorder will be to
control. Cats with IE typically experience their first seizure
Intracranial Lesions (Structural Epilepsy) between 3 and 5 years of age.
Congenital malformations The seizures in dogs and cats with IE are often generalized-
Hydrocephalus
Lissencephaly onset, tonic-clonic, and associated with a loss of conscious-
Neoplasia ness lasting from 1 to 2 minutes. However, dogs and cats with
Primary brain tumors IE can have a variety of focal-onset seizures or a combination
Metastatic tumors of focal-onset and generalized seizures. Some dog breeds,
Inflammatory disease especially Labrador Retrievers and Miniature Poodles, very
Infectious inflammatory diseases commonly experience a mild generalized type of seizure
Meningoencephalitis of unknown etiology (dogs) during which they maintain consciousness but exhibit stag-
Granulomatous meningoencephalitis gering, loss of balance, confusion, a crouched posture or
Necrotizing meningoencephalitis crawling stance, uncontrollable trembling, or muscular
Necrotizing leukoencephalitis rigidity. In Retrievers, common triggers for these unusual
Vascular disease seizures include exercise, excitement, or hyperventilation,
Hemorrhage
Infarct prompting some diagnostic confusion with Exercise Induced
Metabolic storage diseases Collapse (EIC, see page 1106). Many of these epileptic Lab-
Degenerative conditions rador Retrievers experience a postictal phase, develop more
classical generalized tonic-clonic seizures later in life, and
Scar Tissue–Related Acquired Epilepsy respond to chronic oral anticonvulsant therapy, confirming
Idiopathic Epilepsy (Primary Epileptic Seizures) that these paroxysmal events are seizures.
The frequency of seizures varies greatly between dogs and
cats with IE, but seizures typically recur at regular intervals,
with weeks or months intervening between seizures. As the
DIFFERENTIAL DIAGNOSIS animal ages, the frequency and severity of seizures may
increase, especially in large-breed dogs. In some dogs, par-
The differential diagnosis for a patient with seizures includes ticularly large breeds, seizures can eventually occur in clus-
IE, intracranial disease, scar tissue–related acquired epilepsy, ters in which multiple seizures occur during a 24-hour
and extracranial disorders (see Box 62.2). period. Cluster seizures are not seen in association with the
first observed seizure in most dogs or cats with IE, so this
IDIOPATHIC EPILEPSY presentation should prompt consideration of intracranial
IE is the most common cause of seizures in the dog and is causes. The most common time for seizures to occur in dogs
characterized by repeated episodes of seizures with no and cats with IE is when an affected animal is sleeping, drift-
demonstrable cause. Affected dogs are normal between sei- ing off to sleep, or waking up abruptly, but in some patients
zures. The diagnosis can be suspected clinically based on seizures seem to be provoked by specific stimuli such as
breed, age of onset, normal interictal neurologic examina- certain sounds, excitement, hyperventilation, or exercise.
tion, typical seizure recurrence pattern, and failure to pro- IE is the most likely diagnosis in a young adult, neurologi-
gress to systemic or neurologic abnormalities over time, but cally normal animal with a long history (>1 year) of a non-
the diagnosis remains uncertain unless diagnostic evaluation progressive intermittent seizure disorder and a lengthy
has eliminated metabolic and structural causes for seizures. interictal period (>4 weeks). The diagnosis of IE is one of