Page 1122 - Small Animal Internal Medicine, 6th Edition

1094 PART IX Nervous System and Neuromuscular Disorders

BOX 62.1 Animals may appear confused, disoriented, or unresponsive
to owner commands while head pressing, pacing, aimlessly
VetBooks.ir Paroxysmal Disorders Confused With Epileptic Seizures walking, circling, or staggering. Some complex focal seizures
are associated with episodes of howling, unprovoked aggres-
Syncope (reduced cerebral blood flow)
Cardiac arrhythmias sion, or extreme fearfulness. “Rage syndrome” or “episodic
dyscontrol” in St. Bernards and Springer Spaniels may be a
Hypotension complex focal seizure disorder.
Episodic weakness
Hypoglycemia Reflex seizures are seizures that can be consistently pro-
Low blood cortisol voked by specific stimuli or events. The most common pre-
Electrolyte disturbances cipitating factor in people is a flickering light, but certain
Myasthenia gravis sounds and eating have also been identified as triggers.
Acute vestibular “attacks” Reflex focal, generalized, or myoclonic seizures in response
Sleep disorders to high-pitched repetitive sound stimuli have been well
Narcolepsy described in cats, characterizing a disorder called feline
Cataplexy audiogenic reflex seizures. Wirehaired Dachshunds with
Movement disorders (dyskinesias) Lafora disease have been reported to have myoclonic sei-
Exercise-induced weakness or collapse disorders zures triggered by auditory and visual stimuli.
dynamin-associated Exercise-Induced Collapse (dEIC)
Border Collie collapse
SEIZURE CLASSIFICATION AND
LOCALIZATION
Although it is often stated that partial motor seizures are
associated with focal intracranial pathology, many dogs and Seizure disorders can be classified according to their cause
cats with idiopathic epilepsy (IE) experience focal seizures as being idiopathic, intracranial, or extracranial in origin
with or without progression to generalized seizures. Focal (Box 62.2). IE is the most common cause of recurrent sei-
motor seizure manifestations may include abnormal move- zures in dogs but is less common in cats. Animals with IE
ments or postures such as turning of the head to one side, have no identifiable extracranial or intracranial cause for
focal twitching, rhythmic contraction of limb or facial their seizures, are neurologically normal between seizures,
muscles, lip smacking, or chewing movements. Labrador and their seizures are presumed to be genetically based.
Retrievers, Poodles, and occasionally other breeds may expe- Intracranial (structural) causes (e.g., anomaly, inflammation,
rience partial seizures that resemble episodes of staggering, neoplasia, infarct, trauma, scar) are responsible for seizures
loss of balance, confusion, trembling, or crawling without in approximately 35% of dogs and most cats with seizures
loss of consciousness. Circling, rapid running, and climbing (see Chapter 60). Extracranial causes of seizures such as
activity is common in epileptic cats and may suggest tempo- ingestion of toxins or metabolic or endocrine derangements
ral lobe involvement. Focal sensory seizures can cause tin- occur less frequently (see Box 62.2).
gling, pain, or visual hallucinations, resulting in tail chasing, Seizure activity always indicates a functional or struc-
limb chewing, compulsive digging, or “fly biting.” It can be tural abnormality of the forebrain, particularly of the
very difficult to distinguish sensory seizures from compul- frontal or temporal lobes of the cerebrum. Metabolic and
sive stereotypic behavior in dogs. toxic disorders can cause functional alterations of the
Repetitive episodes of autonomic signs may occur as balance between inhibitory and excitatory neurotrans-
unusual manifestations of a focal seizure disorder. Signs may mitters, leading to seizures. Defined localizing neurologic
include vomiting, diarrhea, apparent abdominal discomfort, deficits are unlikely to be detected interictally (between
drooling, repetitive swallowing or gulping, compulsive seizures) in patients with extracranial causes of seizures.
licking of the carpet or floor, or eating grass. Signs may last Animals with an intracranial lesion causing seizures typi-
for hours rather than the seconds to minutes usually associ- cally exhibit multiple signs localizing disease to the fore-
ated with epileptic seizures. Affected dogs are normal brain, including behavior change, circling toward the side
between episodes, and extensive gastrointestinal evaluations of the lesion, contralateral hemiparesis and postural reac-
looking for a cause of their signs are typically negative. Many tion deficits, and contralateral vision loss and facial hypal-
affected dogs have resolution of their episodes with chronic gesia. Animals with small intracranial lesions will, however,
oral anticonvulsant therapy, supporting the suspicion that sometimes be normal interictally, with no other identifiable
these are seizure events. A phenobarbital (PB)-responsive neurologic deficits.
syndrome of drooling, retching, and dysphagia in dogs with IE is a condition wherein the seizure threshold is
painful enlargement of the mandibular salivary glands and decreased. This disorder has been shown to be inherited in
salivary gland necrosis likely also represents a focal seizure a few dog breeds, and a familial basis for the condition is
with prominent autonomic signs. suspected in others. Affected animals are normal interictally,
Complex focal seizures, also known as psychomotor seizures and extensive diagnostic evaluation, including histologic
or automatisms, are focal seizures with altered mentation. examination of the brain, is normal.