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By Dr. Richard Joseph
A seizure, caused by a
sudden short circuiting of the front 2 compartments of the brain, is a sign
that the brain is electrically unstable. Not all seizures are alike.
Localized discharges lead to focal motor seizures which result in part of
the face or body twitching. Complex discharges result in signs such as fly
biting, tail chasing, excessive swallowing or aggression. Generalized brain
dysrhythmia causes major motor seizure, or convulsive activity (or ictus)
that typically lasts for 30 seconds to a couple of minutes of purposeless
movements, involuntary releases (salivation, urination and/or defecation)
and loss of consciousness; and is followed by a recovery phase (or
post-ictus) characterized by countless changes in behavior, intellect,
personality and habits which lasts for several minutes up to 24 hours.
Animals who have
seizures do not suffer and usually are ready to resume their pre-seizure
activity without consequence. Seizures are not considered life threatening
unless a major motor seizure lasts longer than five minutes (status
epilepticus) or an animal has multiple seizures in an hour (sequence
clusters). In either of these cases the animal’s body temperature can rise
and result in heat stroke, fatal cardiac arrhythmias, pulmonary edema, brain
damage and death. In these cases, seeking emergency veterinary care can be
life saving.
Seizures can be caused by disorders of internal organs or by primary brain
disease. If a clear cause cannot be identified, recurrent seizures are
termed idiopathic epilepsy. Whenever possible, it is important to identify
and treat the cause of seizures –as well as the seizures themselves- so that
the problem does not get worse.
Recommended diagnostic
tests are based on age of onset of seizures and results of neurologic and
general physical exam findings. All animals undergo complete blood count and
chemistry, while other diagnostic considerations include urinalysis, hormone
assays, liver function testing, ultrasound, blood pressure measurement and
thoracic radiographs. Brain magnetic resonance imaging (MRI) is especially
important to rule out evidence of structural disease such as a tumor,
stroke, hydrocephalus and encephalitis (or brain inflammation) and is
typically not necessary in animals with onset of seizures less than 3 years
old if they that have normal neurologic exam findings between seizures.
Cerebrospinal fluid (CSF) analysis is important in attempting to determine
whether inflammation is an immune system problem or related to infection; in
rare cases it can diagnose cancer (ie Lymphoma).
If isolated seizures occur more often than every 4-6 weeks, or if clusters
(multiple seizures in a day or couple of days) develop, then starting a
preventative anti-convulsant is recommended. Phenobarbital has the advantage
of being 75% effective when used alone so it is a good first choice anti-convulsant.
Most animals acclimate to sedative effects and adjust to the increased
thirst, urination and appetite that often occur. Biannual monitoring of your
pet’s chemistry profile is recommended to be on alert for significantly
elevated liver enzymes, which require dose adjustments. The development of
liver disease with routine phenobarbital dosages that attain a low to mid
range therapeutic level is uncommon. Other anticonvulsant choices include
Potassium Bromide (KBr) which is available from veterinary compounding
pharmacies, since it it is not an approved drug in United States. KBr is
about 65% effective as sole agent. Though KBr is not metabolized by liver,
it has a long half life so should be loaded by administering a higher
initial dosages in order to get up blood levels. Diet should be constant
while on KBr because changes in chloride intake will inversely affect blood
level. Finally, KBr has sedative effects and may increase risk in dogs of
developing pancreatitis or megaesophagus. Some anti-convulsants used in
people are now more commonly prescribed to pets because generic brands have
made cost less of an issue. These drugs tend to be 50% effective at best as
sole agents in controlling seizures and include Zonisamide, Levetiracetam
(both which tend to be non-sedating) and Gabapentin. These drugs are more
commonly prescribed as add ons when Phenobarbital and/or KBr are
ineffective. Zonisamide is dosed twice daily, It may cause decreased
appetite in a small percentage of animals. The highest capsule formulation
is 100mg, so it may be costly for giant breeds needing maximum dosage.
Levetiracetam is dosed three times daily, is not metabolized by liver and
can be given intravenously in animals with emergency seizures. Other
treatments for refractory seizures that have been tried with variable
success include supplements, acupuncture, vagal nerve stimulation device and
even surgery.
Epilepsy generally is a manageable disease; allowing most animals to enjoy
life with their seizures being largely controlled, A smaller percentage of
animals have refractory seizures, which are resistant or too strong for
medication. These animals require more frequent veterinary visits,
monitoring, adjustment of therapies, and family patience. With each new drug
combination there is a 1-2 week transition period where the animal needs to
acclimate to the new therapy. Unfortunately, seizure frequency and severity
are predictably unpredictable; in the vast majority of cases there is no
clear "trigger" (ie full moon, high tide, diet, etc) that precipitates the
seizurem so drug therapy is recommended when seizures are frequent or
potentially life threatening.
Dr. Richard Joseph, Richard
Joseph DVM, DACVIM (Neurology), is Co-Founder, Managing Partner, and
Medical Director at
Animal Specialty Center in Yonkers, NY. He has treated many
AABR dogs.
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il
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