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View Full Version : Low T4 levels despite levothroxine. What could it be?



big_e
09-06-2011, 11:40 PM
I have an 11 pound 8 year old male toy poodle named Vince. In June I took him to the vet for the following symptoms.

* A skin infection that would not heal
* Blacking of the skin on the belly and around areas where the skin lesions occured and a loss of fur at the skin lesions
* Apparent weight gain
* Lethargy, mental dullness, lost the ability to run up stairs and jump on the bed.
* Low appetite, but no diarrhea or vomiting.
* The vet found his pulse rate to be low for a dog his size
* Rough moist skin on the belly with hyperpigmentation.

I took him to the vet and she ran a routine blood panel, prescribed antibotics and steroids to deal with the skin infection. The blood work came back normal for kidney and liver functions, however T4 levels were extremely low and antibodies measured high. She prescribed levothroxine in a generic chewable form at a dosage of .175 mg once daily for an 11 pound dog. He was a this dosage for about 6 weeks.

The steroids did cause a ravenous appetite and greatly increased urination. The skin lesions started to heal, However after the steroids ran out but, before the antibotics ran out the treatment failed and the lesions started coming back.

The vet prescribed Simplicef and performed another T4 screening. Results were still very low. The levothroxine dosage was doubled to .175 mg twice daily for a total daily dosage of .35 mg a day. He has been at this dosage for about 5 weeks.

After the doubling of the dosage there was noticable improvement in his condition. Hyperpigmentation has greatly decreased and the skin on his belly is thinner, softer, and drier. He had greatly increased mental sharpness, increased play. His gait has changed to more of a prance and he can now run up stairs. He recently regained the ability to jump on the bed. The throxine did not cause him to lose weight.

However several weeks after the Simplicef ran out the skin lesions slowly returned, but was less severe than the previous outbreaks. He also got a mild ear infection.

A few days ago I took him back for another T4 screening about 9 hours after his last dose. The vet prescribed another round of Simplicef and some ear medication. The results of blood panel came back and his T4 levels are still too low.

What happens next the vet has yet to decide, she seems to be stumped. She says she will consult an endocrinologist to determine the next step, but she now thinks I will have to taper down the levothroxine to nothing, so they can send a blood sample to MSU for a full Thyroid panel.

Now I am getting scared. The failure of the levothroxine to bring up the T4 could mean serious illness like cancer. The vet medical papers I'm reading say that other illnesses can cause bad T4 levels, but they don't exactly say what.

There is addison's disease, but he never had the "addison's crisis" with vomiting and diarrhea. Vince is a nervous dog and being upset does not cause those symptoms. I don't know if addisons will mess with T4.

There is also cushings disease, the opposite. The symptoms he is missing are he does not seek cold, he does not pant, he does not have excessive thirst. He did exhibit noticably increased thrist, appetite, and urination in response to the steroids. The cushings like symptoms he does have are frequent skin infections, hyperpigmentation, and low T-4

If I were to completely disregard the bloodwork, I would say the Levothroxine was working, but slowly. However, the T4 levels seem to disagree. I'm lucky, The T4 levels could be flubbed to do the 9 hours since last dosage, the particular brand of Throxine not metabolizing well, or the dog didn't eat all the pill.

Is the hypothyroidism and low T-4 levels despite levothroxine a symptom of Cushings? I'm not finding much about what could cause that to happen. I am concerned that the vet taking him off the levothroxine will reverse his gains.

Harley PoMMom
09-07-2011, 12:34 AM
Hi and welcome!

Cushing's can cause what is called "Sick Euthyroid Syndrome." In this situation the thyroid gland is normal, but there are factors that are suppressing it from secreting a normal amount of thyroxine into the bloodstream. These factors include medications like cortisone, valium, anticonvulsants, and sulfa antimicrobials. Diseases like Cushing's disease, diabetes mellitus, chronic renal failure, liver disease, and Addison's disease can also cause "Sick Euthyroid Syndrome."

Mange can form scabs and there are several different types of mange, with the two most common types being sarcoptic mange or scabies and demodectic mange. Both are caused by tiny parasitic mites that burrow into the skin, which results in skin irritation, hair loss, and crusting or scabs forming.

To find mites, it is necessary to obtain skin scrapings from affected areas. A punch biopsy may be needed if skin-scraping results are negative and the index of suspicion for demodicosis is high.

Strong symptoms are a huge part of making the diagnosis of Cushing's and since Vince does not display the obvious clinical signs such as excessive thirst and urination and a ravenous appetite, a Cushing's diagnosis is unlikey.

If you are thinking about getting a thyroid panel done, if it were me, I would have it sent to Dr. Dodds. This is quoted from her website:
The main reason for sending Dr. Jean Dodds / HEMOPET the serum samples instead of having the testing done locally, is that HEMOPET is the only group routinely offering expert clinical interpretive diagnostic comments that take into account the age, sex, and breed type of the animal. This often means an expected normal reference range for an individual pet that differs from the test lab's generic broad reference range. Practitioners usually are unaware of these differences, which have been established by published research and Dr. Dodds' many years (46 years this year - 2010) of clinical and research experience.http://www.itsfortheanimals.com/HEMOPET.HTM

I was wondering if you could get copies of all test/s that were done on Vince and post the results here, this would help us to give you more meaningful feedback.

Please know we will help you in any way we can so do not hesitate to ask any and all questions.

Love and hugs,
Lori

Harley PoMMom
09-07-2011, 12:53 AM
This post is from one of our members whose dog had Hypothyroidism, this member sought advice from Dr. Dodds and I think it might be useful:


Thyroid update:
1 month ago we did an unplanned Thyroid test while doing a stim test to safe costs (per vets suggestion). Back then I was really preoccupied absorbing all the Cushings information/getting him on a proper loading protocol so I did not think twice when we drew blood at 3.30 pm that day.
Back then his T4 came back at 19 nmol/L (1.4 ug/dL ) (should be between 28.3 -57.9 nmol/L or 2.20 – 4.50 mg/dL which is the optimum geriatric level ). So I upped the dose from 0.4 to 0.6. On Saturday his T4 was 81 nmol (6.29 ug/dL) – way too high. I knew I had to decrease the dose but I kept thinking about these numbers and then it suddenly struck me ..... Shelf-live is about 9h, the T4 test was done 9.5h post pilling – yikes :eek:. So he is back on 0.4 mg of Soloxine 2x per day – poor guy should not have to go through these up and downs needlessly.:(:(:( The thyroid test 2 months ago was our first test since he started Soloxine – back then I did not know thyroid levels peak 4-6h post pill so this time I made sure we used a blood sample taken within the 4-6 h window but I don’t think these type of things should not be my sole responsibility. Very frustrating.

I previously had emailed Dr. Jean Doods with some questions and thought I post my questions and Jeans responses here as well for anybody who might be interested.

“Optimal therapeutic response levels should be in the upper 1/3 to 25% above the upper limits of the resting optimal ranges at 4-6 hours post-BID thyroid medication.”
Explanation:
Geriatric Therapeutic Optimal Levels:
T4 2.20 – 4.50 ug/dL
FT4 0.70 - 2.00 ug/dL
T3 40 – 70 ug/dL
FT3 1.6 - 3.5 ug/mL

Question: How often should I have his thyroid function tested and what tests should be done?
Answer: Every 6-12 months; test T4 and freeT4.
Question: I have read that we should test not only for T4 but also Free T4 – is this correct and what does the Free T4 value in conjunction with the T4 value supposed to tell me?
Answer: Definitely, because freeT4 is the biologically active tiny fraction [0.1 %] of total T4 .
Question: How to convert T4 value from nmol/L to ug/dL
Answer: you must divide the nmol/L by 12.87 to convert it to ug/dL


Checking the thyroid function at 4-6 hours post-BID thyroid medication is very important. Seeing that Vince's thyroid test was 9 hour after his medication, I believe, would make the results skewed.

StarDeb55
09-07-2011, 01:10 AM
Lori, has given you some great info about thyroid. I just wanted to confirm that my GP vet who is treating my Lhasa for hypothyroid has always insisted that his blood draws been done 4-5 hours post pill, absolutely no later. 9 hours post pill, IMO, basically invalidated this test. Also, at any point in time was an actual free T4 by ED done?

Welcome to our group! We're here to help in anyway we can. I do have a couple of other questions. Is your boy still on any type of steroid, whether it is oral or topical, such as ear drops? There is one simple screening test that can be done called a urine cortisol/creatinine ratio which if negative would absolutely rule out Cushing's. It is a simple, reasonably inexpensive test that you could actually collect the urine at home. If the UCCR was positive, all that means is Cushing's is a possibility, further testing required.

Debbie