Epileptic Silken Windhound With Low Thyroid on Phenobarbital
by Kathleen
(Woodinville, WA)
My dog suffers from epilepsy. At about 3 years old, his first seizures initially were about a month apart. After he was on Phenobarbital for a year, I reduced his dosage and he was seizure-free for 6 months, at which time I increased his dosage to previous levels. Magic took Phenobarbitol for 3 years; during that time I saw 5 different vets, and not once did any vet recommend testing his thyroid. Earlier this year, when I noted a glassy stare, weight gain, and panting I finally asked for an ACTH Stimulation Test and a thyroid panel.
The Cushing's test came back negative, but the thyroid panel showed that Magic had NO measurable thyroid in his system.
We immediately started him on thyroid, but the first follow up showed that a month and a half of thyroid supplementation still hadn't gotten his levels up to normal. Further research by me showed that Phenobarbital can hasten the metabolism of thyroid and make the supplementation less effective.
I've upped the thyroid dose. The glassy stare is gone and his personality is coming back. But he still pants a lot and shows a lot of fatigue. The extra weight isn't coming off. We will go back to the vet shortly to see how close to normal his thyroid levels are now.
According to Jean Dodds, DVM, the seizures could be as a result of the hypothyroid condition. Of course, there's no way to know for sure what he source of them is. Obvioulsy, I would like to get him off the Phenobarbital if he doesn't need it.
I understand that the ACTH stim test isn't 100% effective and can have false negatives, so I'm considering doing a different test to see if I can get the diagnosis confirmed.
There isn't much guidance out there for someone in this situation. Could the Phenobarbital be starting to cause breathing difficulties that result in panting? How long should
I'm appalled at the veterinary community, who seems to be treating statistics and acting like I have an unlimited amount of money to run tests that aren't conclusive anyway. I've learned more online than from any of the multiple experienced vets that I've seen.
I need someone to help me develop a plan to get to the heart of Magic's health issues.
You're right that phenobarbital can lower thyroid test results and can speed up how the body breaks down thyroid medication, so thyroid levels need regular rechecks in dogs on both drugs. Phenobarbital can also cause increased hunger and weight gain, and a dog that is still hypothyroid can be tired and heavy. Panting has many causes, so it's worth raising with your vet rather than assuming it is from either drug.
Hypothyroidism is not considered a common cause of seizures in dogs, and his age at the first seizure (3 years) fits idiopathic epilepsy. That means stopping phenobarbital is a real risk. Please don't lower or stop the dose on your own; reducing it too quickly can trigger severe, even life-threatening seizures. If you and your vet decide to try, it should be a slow, planned taper, typically only after a long seizure-free period, with phenobarbital blood levels and liver tests checked along the way.
A neurologist (or an internal medicine specialist for the thyroid and Cushing's questions) can help you build one coordinated plan. Ask about a phenobarbital blood level, liver function tests and a full thyroid recheck. Keeping a seizure diary will also help any vet judge how well his epilepsy is controlled.
Our page on seizures in dogs covers epilepsy medications and why they shouldn't be stopped suddenly.
This is general information, not a diagnosis. Please follow your own vet's advice.
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