scott@vtx-cpd.com

Replying to Þórunn J. 22/04/2024 - 23:30

Hi Thorunn,

Thank you for sharing this interesting case.

This is a tricky case! Given the improvement in your patient’s clinical signs and the initial laboratory findings, I can understand why you might want to continue the medications. What are the owners feelings? Would they be OK with stopping medication? What was the cholesterol at the point of diagnosis?

Th good thing is that hypothyroidism is not life threatening. I would stop medication and only re-test if you had concerning clinical signs develop again. Worst case scenario would be having to start the medication again.

I would not run any more tests when the patient is on medication. If the patient comes off medication and you are testing again, I would consider T4, TSH, TGAA and possibly free T4.

Given the mitral valve disease, regular monitoring of cardiac status is important. Ensure that the thyroid medication does not exacerbate any cardiac issues. I will get Liz to comment on the heart side of things.

Honestly, I would not perform routine testing in this dog after coming off meds. I would test again if clinical signs creep in!

Hope that makes sense.

Scott 🙂

Replying to Neus E. 20/04/2024 - 15:09

Hi Neus,

It’s been a pleasure having you involved in the VTX course once again! Thank you for your active participation, engaging questions, and insightful thoughts. Your contributions have enhanced our discussions and learning experience.

All the best to you too!

Warm regards,

Scott x

Replying to Mónica P. 20/04/2024 - 09:51

Hi Mónica,

I’m glad to hear you’ve been learning a lot! Let’s address your questions:

It would be very uncommon to measure T3 in a practical stetting. I have never measured it in a clinical case. If there is a cat with a high clinical suspicion of hyperthyroidism with a normal TT4, I would consider free T4 by ED helpful in this stetting.

When a cat presents with symptoms of hyperthyroidism but has a normal TT4 result, it can still be beneficial to repeat the TT4 test on another day to confirm the result. Additionally, adding a measurement of free T4 (fT4) can help provide a more comprehensive assessment of thyroid function, as fT4 is the biologically active form of thyroid hormone.

Repeating total T4 or running free T4 would both be options. Overall, if I have a normal total T4 with a high index of suspicion my next step would be to run a free T4.

Hill’s y/d is specifically formulated to manage hyperthyroidism in cats by restricting iodine intake, which is necessary for thyroid hormone production. While it can be beneficial for managing hyperthyroidism, it may not be the ideal choice for managing concurrent chronic kidney disease (CKD). Hill’s k/d and Royal Canin Renal are formulated to support kidney function in cats with CKD and may be more appropriate for cats with both conditions. I would not use y/d with renal cats and would prioritise the renal diet as we know this can have a more specific and important impact on survival. Do you have access to the transdermal methimazole? This article is an interesting read:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9543258/

When assessing thyroid function in a cat on prednisolone or other corticosteroids, it’s generally recommended to wait at least 2-4 weeks after discontinuing the medication before testing thyroid hormones. This allows time for the corticosteroid to clear from the system and for thyroid hormone levels to stabilize. However, the exact duration may vary depending on the individual cat and the specific corticosteroid used. If this was not possible, free T4 might be a good option here.

I hope this helps clarify things for you! If you have any more questions, feel free to ask.

Kind regards,

Scott 🙂

Replying to Janette B. 19/04/2024 - 19:59

Hello Janette!

What an honour to have you here. Thank you so much for working with us and providing such a brilliant course!

Hope you are having a great weekend.

Scott 🙂

Replying to Mónica P. 14/04/2024 - 08:27

Hello Mónica,

I hope you are well. I have popped some thoughts below:

1. Thyroglobulin autoantibodies (TgAA) are specific for dogs are used to diagnose autoimmune thyroiditis, which can lead to hypothyroidism. The test should be specific for veterinary use and not cross-react with human antibodies. I would double check with the lab you are using, but the veterinary labs I checked with are canine specific.

2. Fasting for Thyroid Hormone Testing: No, thyroid hormone levels do not need to be tested after fasting. Unlike some other tests, such as cholesterol, fasting does not significantly affect thyroid hormone levels. This is the protocol I have always used. I am often testing thyroid values along with other parameters, so my patients might be fasted for other reasons. I also found some evidence in human medicine that there may be an effect:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4171896/

I will chat to Yvonne regarding this question as she will have the most up to date lab based information.

3. Here are the conversions for TSH:

1 ng/ml = 1 µg/L
0.5 µg/L = 0.5 ng/ml

I do not have a table, I am afraid.

4. Since phenobarbital can affect thyroid hormone levels, it’s best to test thyroid function before starting phenobarbital therapy if possible. If a patient is already on phenobarbital, testing can still be done, but the results should be interpreted with caution, knowing that phenobarbital could potentially affect the results. Ultimately, it often will come down to clinical suspicion. I would have to be VERY clinically suspicious that these patients had hypothyroidism before starting treatment.

5. The frequency of levothyroxine (T4) administration depends on the individual patient. While some guidelines recommend once daily dosing for T4 levels above 7.5 µg/dL, others may suggest adjusting the dosage. In practice, once daily dosing is often practical and effective, especially for owner compliance. However, I find that the majority of dogs do better on twice daily dosing overall.

6. The maximum recommended dosage of levothyroxine is usually around 0.8 mg twice daily. In giant breed dogs, dosages should be individualized based on the patient’s response to treatment and monitoring of thyroid hormone levels. I am comfortable increasing this dose further as long as I am confident that we have an accurate diagnosis and the patient requires the higher dose. I would be monitoring carefully.

7. Successful response in dogs treated once daily is associated with a median peak TT4 concentration (6 hours after administration) of approximately 4 mcg/dL (50 nmol/L). Values below 2.7 mcg/dL (35 nmol/L) are usually associated with an inadequate clinical response, and an increase in dosage is indicated. Markedly increased peak TT4 concentrations >7 mcg/dL (>90 nmol/L) occasionally occur. Although dogs are usually resistant to severe clinical thyrotoxicosis, such values should prompt a decreased dosage.

Regarding the Dogue de Bordeaux case, it’s true that some breeds, including the Dogue de Bordeaux, can have lower thyroid hormone concentrations compared to other breeds, so interpreting the results should take this into consideration.

Feel free to ask if you have any more questions or need further clarification!

Scott 🙂

Replying to Hayley O. 16/04/2024 - 21:15

Hey Hayley.

Thanks for the brilliant questions:

1. Any amount of protein on a urine dipstick can be a reason for further investigation, especially if other clinical signs or laboratory abnormalities are present. However, a threshold of 1+ or greater on the dipstick is often used to raise concern for proteinuria. It really does depend on the case. I would not be rushing to perform UPC in all cases, especially if you are treating/managing other problems. I would want to demonstrate that it was a persistent abnormality before investigating further. This is the same for UPC; it is really important to demonstrate that it is a persistent and consistent finding.

2. It’s generally advisable to confirm persistent proteinuria with a urine protein-to-creatinine ratio (UPCR) from at least one home caught first-morning sample (a more concentrated sample) before initiating further diagnostics or treatment. If the UPCR is borderline, it’s recommended to retest in 2-4 weeks to assess for persistence or resolution. This timeframe allows for monitoring without unnecessary delay in case intervention is needed. It also gives time to resolve any concurrent disease processes.

3. Proteinuria can occur in intact animals, but it is not considered a normal finding. It should be quantified and further investigated, especially if persistent or associated with other abnormalities.

4. Quantification of proteinuria is ideally done by UPCR on a first-morning sample. If cystocentesis is performed for another reason, such as collecting a urine culture, the urine can be analysed for protein at the same time. However, if the animal is not showing clinical signs and the proteinuria is only detected on dipstick, it’s reasonable to start with a UPCR from a voided sample and proceed based on those results.

I hope that helps!

Scott 🙂

Replying to Talia C. 16/04/2024 - 16:49

I also think it is a really good way of assessing the urethra.

We often perform a rectal to assess the prostate, but you can get a good idea of urethral thickening in many dogs.

I am always surprised by the number of owners that do not report melena, but the rectal exam says otherwise!

Scott 🙂