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How do we diagnose idiopathic epilepsy?
Idiopathic epilepsy is a diagnosis by elimination. That is, we look for other causes of seizures and if we can't find any, we make the diagnosis of idiopathic epilepsy. How aggressively we search for an underlying cause is a matter of clinical judgement. We always recommend a minimum work-up for any dog having seizures. This will provide us with clues to a possible underlying disease and provide the baseline from which to watch for potential side effects of antiepileptic drugs.
Since your veterinarian may not witness one of your pet's seizures, they are very dependant upon your description of the episode. This will help them decide whether these events are indeed seizures. Other problems such as fainting or dizzy spells can also come and go like seizures and may look similar to the untrained eye. Thus, your veterinarian will need a clear description of what you observe during the episode to help make that distinction. They will also be determining what type of seizure your pet is experiencing. Write down a description of what you saw as soon as possible after the episode. If you can, make a videotape of the episode to show your veterinarian or the neurologist.
In order to rule out some diseases, we would need further tests. If the animal is outside the 1-3 year old range when idiopathic epilepsy typically starts, or has any abnormalities on examination that hint of a cause, we strongly recommend such testing. Your veterinarian may refer you to a neurologist for some of these tests. Even if an animal is within the "idiopathic epilepsy" age range, we can't be sure it's idiopathic unless we perform the full compliment of tests. One study (Podell 1995) showed that over 1/3 of the dogs between 1 and 5 years of age had an identifiable cause for the seizures. Thus we can make a case for aggressive testing in any epileptic dog, but need to weigh the additional cost involved into the equation.
The electroencephalogram (EEG) is a useful tool in diagnosing epilepsy, but has serious drawbacks in animals. When we see abnormalities in the EEG, that tells us this is indeed a seizure and may help us pinpoint the source. The trouble is, those EEG abnormalities, like the seizures, can come and go. If they don't happen while we are recording the EEG, we will not see them. Recording an EEG in an awake animal is difficult, so we often have to sedate or anesthetize them to get an adequate recording. The drugs used for the sedation/anesthesia also affect the EEG. Thus, we often make the diagnoses of epilepsy based on the clinical signs and don't require EEG confirmation of the disease.
Thyroid function and epilepsy
There is a great deal of controversy (largely unnecessary) about the role of the thyroid in canine epilepsy. The thyroid hormones regulate metabolism. Too much thyroid activity, and the metabolism runs too fast. The result is weight loss, nervousness, high blood pressure, and so on. Too little thyroid activity, and metabolism runs too slow. This results in weight gain, lethargy, high cholesterol levels, and so on. Normally, dogs don't develop atherosclerosis: the hardening of the arteries that predisposes people to heart attacks and strokes. The high cholesterol that accompanies hypothyroidism (too little thyroid hormone) can, however, lead to atherosclerosis and strokes in dogs. Likewise the high blood pressure that accompanies hyperthyroidism (too much thyroid hormone) can also predispose the dog to stroke. So the dog needs "Goldilocks levels" of thyroid hormone: not too much, not too little, but just right. If the levels are outside that range, then we could have problems which could cause epilepsy.
Thyroid function tests are affected by many things, including stress and medications. Several recent studies have demonstrated that phenobarbital therapy causes falsely low values on some thyroid tests. Recent seizures will also cause false lowering of the values, presumably due to the stress they cause. So test results need to be interpreted with these caveats in mind. If an animal tests truly low on thyroid function, then a trial of thyroid supplementation is indicated. If an animal has normal thyroid tests or fits with what we expect from the effects of the medication or seizures, then there is no reason to supplement thyroid hormones
What about liver shunts?
One of the jobs of the liver is to ensure that only the good stuff from the food we eat gets into the body. Dogs are notorious for eating disgusting things, such as the moldy cheese out of the garbage, and their liver is responsible for keeping toxins from affecting the body. In addition, the action of bacteria in the intestines on food can produce toxic byproducts which the liver deals with. All the blood coming from the intestines goes through the liver first, where it is cleansed of toxins before going around the rest of the body. When an embryo is safe in the mother's womb, the mother's liver takes care of that job, and the embryo doesn't need to worry about it. As a result, the blood from the intestines bypasses the liver in the embryo through a separate vessel called a shunt. When the pup is born, however, the liver needs to switch gears and start doing it's job of cleaning the blood from the intestines. So the shunt closes down and blood is run through the liver to be cleansed before it gets to the brain.
If the shunt fails to shut down like it should, then blood will continue to bypass the liver. A shunt that is present from birth is called a congenital shunt. The liver then doesn't get a chance to remove the bad stuff until it's already circulating around the body. Many of the toxins that the liver would normally clean up can affect the brain, and seizures can be one of the effects.
Shunts can also be acquired later in life. If the liver is diseased, blood may have a hard time flowing through the sick liver, leading to a back-pressure in the vessels coming from the intestines. If that back-pressure gets high enough, the blood may find an alternative, less resistant, pathway. The result is the same as the congenital shunt; blood bypasses the liver and toxins affect the brain.
Both because liver problems can cause seizures and because many of the medications used to treat epilepsy can injure the liver, we recommend liver function tests as part of the initial work-up and as part of the regular check-ups. The liver enzyme tests which are part of a routine chemistry profile may not be adequate to detect liver shunts and liver function tests, such as bile acids or ammonia, are necessary.
Other tests may be necessary
Depending upon your pet's age, type of seizure, and findings on the minimum work-up, your veterinarian may also recommend further tests. Advanced imaging, such as MRI or CT scans, is necessary to be able to actually see the brain. Regular radiographs (X-rays) can tell us about the bones of the skull, but not the brain itself. Such imaging is becoming more readily available for animals at referral centers. By imaging the brain, we can diagnose diseases such as brain tumors or hydrocephalus (water on the brain) which can cause seizures.
Infection of the brain (encephalitis) can cause seizures. Canine distemper is the most common cause of encephalitis in dogs and one of the reasons to keep your pets current on their vaccinations. A spinal tap and serum antibody titers will enable your veterinarian to tell if distemper or one of the other causes of encephalitis is the reason for your pet's seizures. Additional blood tests including toxin screens may also be indicated.
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нечем крыть - крой матом
зы:пишу с очепятками, т.к. попугай сгрыз половину кнопок на клаве)))
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