Thyroid cancer?

Dr. Marie replied:

I'm sorry to hear that Mara is having these problems. While I won't be able to give you a diagnosis, I'll give you my thoughts on what you have written about her.

There are a few things that have me concerned about her tests. The first one is her thyroid level. Now, there are different units that can be used to measure T4, but no matter what units are being used I can't say that I have ever seen a dog have a level that is that high. What you are seeing with this T4 level is hyperthyroidism (overactive thyroid). When dogs get thyroid problems they are almost always hypothyroid (underactive thyroid).

Unfortunately the most common reason for a dog to be hyperthyroid is if there is a tumor on the thyroid gland. Usually this tumor can be palpated (felt) by the veterinarian. Thyroid tumors in dogs usually are cancerous and they do tend to spread to the lungs. Unfortunately this can explain the white areas that the vet is seeing on the lungs. Thyroid medicine can help reduce the symptoms of an overactive thyroid, but if there is cancer present then it will not work for long. There are some things that can be done for thyroid cancer such as surgery, chemotherapy and radiation, depending on how aggressive you are willing to be and how much money you are willing to spend.

I'm not too worried about the increase in ALP. This value tends to go extremely high (like in the 700-1400 range) if there is a serious problem. The rest of the blood tests don't have me too concerned.

Has your vet talked to you about the possibility of thyroid cancer? This really is my biggest concern. If you are thinking at all of treating the cancer then it would be worthwhile to ask for a referral to a veterinary oncologist (cancer specialist).

If I have a case like this where I am not sure if I am seeing cancer or inflammation in the lungs I will often send the xrays to a radiologist to get their opinion. But really, when we combine this high thyroid level with the changes in the lungs cancer really does seem likely.

Is there any chance that you have typed the thyroid level incorrectly? Did the vet give you any explanation as to why they felt the level was that high?


I wish I had better news for you. Please let me know if you have more questions.

Dr. Marie.


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Dr. Marie replied:

Ah, will this changes everything! So, ignore my previous answer and let's start again. :)

First of all, a low T4 does not always mean that a dog is hypothyroid. Sometimes if the body is dealing with something else, then the T4 can be low. I usually don't start a dog on thyroid medication unless I have done additional tests to confirm that there is a thyroid problem. Perhaps this has been done already!

I am quite concerned about what you are describing with her breathing, especially when you combine this info with the fact that she had unusual looking xrays. It does sound like some type of cancer is a possibility. This is likely why the vet has put your dog on Prednisone. If there is cancer there, then sometimes the Prednisone will help decrease the inflammation around the tumors and give us a better quality of life for a time.

The Clavaseptin is an antibiotic in case the changes in the lungs are due to infection. However, pneumonia (infection in the lungs) is really not common in dogs. And usually, if we are seeing white patches/spots on an xray this is not infection.

Do you know if you live in an area where fungal diseases are possible? Sometimes it is hard to distinguish between cancer and a fungal disease such as blastomycosis. With that being said, blasto is usually a disease that we see in young dogs.

I think it is best to give your vet a call and let them know that Mara is not improving. It is sounding more and more like there is a cancer present and unfortunately we are limited in what we are going to be able to do for her.

I wish I had better news for you.

Dr. Marie replied:

My experience is that dogs with hypothyroidism have very vague symptoms of lack of appetite, weight gain and panting. It really sounds like there is something more going on here. However, in a case like this I would likely be doing a special test called T4 by equilibrium dialysis which would tell me if this really is a thyroid problem or if it is something called "sick euthyroid". Sick euthyroid means that the thyroid level looks low but it's just because the body is fighting something else.

Yes, the prednisone at this dose can have anti-inflammatory effects and as such will help with pain. There are other medications that your vet may prescribe if they feel that the prednisone is not enough.

Regarding fungal diseases, this is something you could ask your vet about. However, if you live in an area that regularly sees fungal diseases then the vet really would know this. So this makes me think that unfortunately cancer is the most likely explanation.

I think it would be a great idea to phone your vet clinic and let your vet know how Mara is doing now. I would also ask him/her how likely they feel the diagnosis of cancer is.