Hypothyroidism and Hyperthyroidism


also see Parathyroid


Question: Hello Dr. Mike,

I am truly glad that I have discovered your website because as you will see I have a ton of questions regarding hypothyroidism that I would love to get answered.

I have been trying to get answers to my questions for a long time regarding my dog's thyroid condition but have failed. I have read a lot of articles about hypothyroidism on the internet but am still left with questions. As a result, I opted not to treat my dog, Cleo, but now, I am having a change of heart, and feel I don't want to chance it anymore or wait until she becomes sick.

My vet feels that hypothyroidism is a "benign" condition. I, on the other hand, have read articles by Dr. Dodd's and others and feel that hypothyroidism is more serious than my vet appreciates. He also does not support FT4 by equilibrium dialysis feeling that the thyroid panel that I've been getting done for my dog is sufficient (FT4 being measured by chemiluminescent method). I have tried to get a specialist's opinion but my vet told me that there are no endocrinologists in the Toronto area. He did tell me that he contacted two endocrinologists in the States and told me that these specialists supported his opinion to put my dog on a trial treatment of levothyroxine however he would not give me the names of these specialists.

I think in order to give you a clear picture of my dog's medical history I have to give you her thyroid panel results so here goes:

Jan 20, 1998 -Cleo approx 1.5 -2 years old ---------------------------------------------

1) Thyroid Panel

T3 2.1 ref. 1.15-3.10 nmol/L

T4 23.3 ref. 19.0-58.0 nmol/L

TSH 0.11 ref. 0.00-0.35 ng/mL

T3 AA 0.4 ref. 0.0-2.0

T4 AA 0.7 ref. 0.0-2.0 *

FT3 4.83 ref. 2.00-4.60 pmol/L

FT4 22.1 ref. 12.0-45.0 pmol/L

2) Comprehensive biochemistry O.K. except

Urea 8.2 ref. 3.0-8.0 mmol/L

Calcium 2.00 ref. 2.12-2.80 mmol/L

3) Blood Count O.K.

Sept. 21, 1999 - Cleo approx. 3.5 years old ----------------------------------------------------

1) Thyroid Panel

* T3 0.99 ref. 1.15-3.10 nmol/L

* T4 12.8 ref. 19.0-58.0 nmol/L

TSH 0.06 ref. 0.00-0.35 ng/mL

T3 AA 0.4 ref. 0.0-2.0

T4 AA 0.7 ref. 0.0-2.0

FT3 3.00 ref. 2.00-4.60 pmol/L

FT4 14.0 ref. 12.0-45.0 pmol/L

2) Comprehensive Biochemistry O.K.

3) Blood Count O.K.

April 12, 2000 - Cleo approx. 4 years old ---------------------------------------------

1) Thyroid Panel

T3 1.50 ref. 1.15-3.10 nmol/L

* T4 8.9 ref. 19.0-58.0 nmol/L

TSH 0.06 ref. 0.00-0.35 ng/mL

T3 AA 0.2 ref. 0.0-2.0

T4 AA 0.4 ref. 0.0-2.0

FT3 3.50 ref. 2.00-4.60 pmol/L

FT4 19.8 ref. 12.0-45.0 pmol/L

2) Biochemistry O.K. except

Glucose 3.4 ref. 3.6-7.0 mmol/L

* note: only basic biochemistry done

3) Blood Count not done

Oct. 5, 2000 - Cleo approx 4.5 years old --------------------------------------------

1) Thyroid Panel

* T3 1.10 ref. 1.15-3.10 nmol/L

* T4 8.8 ref. 19.0-58.0 nmol/L

TSH 0.11 ref. 0.00-0.35 ng/mL

T3 AA 0.1 ref. 0.0-2.0

T4 AA 0.3 ref. 0.0-2.0

FT3 3.2 ref. 2.00-4.60 pmol/L

FT4 13.4 ref. 12.0-45.0 pmol/L

2) Comprehensive Biochemistry O.K. except

A/G Ratio 1.4 ref. 0.9-1.3 Alk.

Phosphates 23 ref. 24-141 U/L

Glucose 2.1 ref. 3.6-7.0 mmol/L

3) Blood Count O.K.

Now a little about my dog. She appears to be a mix of beagle and another type of scent hound. She's about 5 years old, intact, never been bred, has been on a raw diet (Billinghurst) for over three years plus supplements (kelp, yeast, vit E, flax oil) and usually gets a portion of whatever I'm eating. She is 34 lbs, lean, and gets plenty of exercise. Her coat and skin are in good condition.

In her first year of life she was over vaccinated. I got her from the shelter when she was about a year old. She was vaccinated there (rabies and booster) and then about a month later she had another booster (accidentally). To top it off her previous owners may have vaccinated her too. Since then she has had no vaccinations.

After two years of giving her heartworm preventative I opted to stop that too. Toronto has very few cases of heartworm.

Now her problems...

Every late summer or fall she would get seasonal allergies from being out in the ravines or the country. It seemed like every year she would develop new symptoms but she would always develop hives (except for last year). Her other symptoms included massive hair loss, sensitive sore spots and pustules, excessive itching and scratching, and coughing up clear liquid (I assumed post nasal drip). I first used benadryl to prevent these outbreaks but then I discovered grape seed extract which worked much better. Last year, however, was the best year yet and I didn't have to use anything. Cleo still got very itchy and shedded more than usual but that was it.

After her first heat with me, she developed a stiff hind leg walk where it appears as if she does not bend her knees. She was diagnosed with luxating patella and I even took her to a neurologist because I was worried about spinal disc disease. She too felt that it was Cleo's knees that was making her walk funny. Since then I have had her on and off of glucosamine but it hasn't seemed to help...however I was only giving her 250mg/ day. Now I'm thinking I should try more. I have just recently put her on 500mg/400mg glucosamine/chondroitin especially since she now seems to be waking up from her naps a little stiffer than usual. What dosage do you recommend? And is it necessary to give it with food?

She has always been cold intolerant meaning she begins to shiver even when it's not so cold out. As a result I really bundle her up in the winter time.

Since last summer there's a spot on her nose now about 3mm in diameter where she's been losing pigmentation. It has gotten bigger since last year so it was not caused by scrapping it and she does not eat out of plastic bowls.

Indoors, my dog basically is a couch potato where she usually sleeps for about 16 hours or so, only getting up to eat and pee. But outdoors we go for three hour walks at a time and when she's let go in a country setting, she hunts (runs like crazy) basically until I grab her about 3 hours later. My point is...I don't think she lacks any energy.

So that's about it. I don't think she has obvious symptoms of hypothyroidism but I'm thinking maybe her cold intolerance, stiff walk and loss of pigmentation may be just that.

My vet wanted to put Cleo on a trial treatment of levothyroxine giving her a minimal dosage. He didn't feel that there was a need to check her blood afterwards but rather to watch if she becomes less cold intolerant. I was shocked that he wasn't planning on checking her blood after treatment because I have read that it is very important to get the right dosage. Am I wrong?

I'm also wondering whether the thyroid itself actually loses its ability to produce hormone after levothyroxine treatment has occurred for a long time. My vet told me that it wouldn't because he will only prescribe a minimal dosage so that Cleo's thyroid will keep working. Does this seem right to you? He also told me that a portion of Cleo's thyroid is already dead...what do you think?

I'm confused however whether her blood results thus far even indicate whether Cleo has primary hypothyroidism. I mean wouldn't her TSH have to be much higher and her FT4 lower? Wouldn't she have to have higher levels of autoantibodies? I did read in an article that the presence of autoantibodies can actually cause FT4 to increase so maybe this is the reason why Cleo's FT4 isn't so low...I don't know.

Could it possibly be secondary or tertiary hypothyroidism? Or on the other hand, what about euthyroid illness? Does the fact that Cleo has normal blood counts and chemistry prove that she has none of these? Or are there other tests I should be having done?

Now even if she doesn't have primary hypothyroidism Cleo's T4 and FT4 levels are still low. Would you still recommend putting Cleo on levothyroxine treatment?

I 'm not sure what a trial treatment should be based on. I'm not going to be able to test whether Cleo warms up...because it's no longer cold outside. I'm also wondering whether a dog becoming more cold tolerant on treatment is simply an automatic response to levothyroxine supplementation? I think it's called a "pharmacologic" effect.

I'm wondering whether the disappearance of a symptom like her hind leg stiffness would be a sign that Cleo actually does have primary hypothyroidism? Is it possible that Cleo could regain the lost pigment on her nose while on treatment?

I'm confused because if non-thyroidal illness (NTI) can cause T4 or even FT4 levels to lower than why wouldn't a dog with NTI as opposed to primary hypothyroidism still respond favorably to levothyroxine treatment? My vet told me that Cleo would not respond to treatment if she had only NTI but he didn't explain why.

An article I read stated there are three options for a dog with non-conclusive thyroid results:

1) to wait a few months and see if the dog's symptoms become worse

2) to do a FT4 by equilibrium dialysis along with TSH

3) to do a trial treatment

Well, with regard to:

1) my dog's symptoms have basically stayed the same since I began getting her blood tested about three years ago all except the loss of pigment on her nose which developed in the last year. So does hypothyroidism usually act faster than this?

2) I think I should get a FT4 by equilibrium dialysis done the next time I get my dog's blood checked. Do you advise this?

3) I do not know whether a trial treatment will prove anything.

I plan to be getting Cleo's blood retested in a week or so which would be about 3.5 months after the onset of her last heat. Since she gets her heats every 7-8 months I figure this is mid-cycle and a good time to get her tested.

I'm wondering if the time of day the blood is taken makes much of a difference in the results because I've been getting Cleo tested around mid-afternoon since she usually gets up around 1-2:00 p.m.

Now finally I have to ask if it possible that there is nothing wrong with my dog? Could it be that Cleo's abnormal thyroid results are simply normal for her? The only problem with this rational is that Cleo's results have not remained the same since she was first tested at 1.5 years old. But is it normal for thyroid results to drop this much over a couple of years time?

So if you could let me know what you would do with this dog of mine I would highly appreciate it. I apologize for this lengthy letter but as you can see, I've had a lot of questions about my dog's condition and I haven't been able to find the answers...eventhough I've tried.

Your response would be more than appreciated!

Thanks, Carolyn

Answer: Carolyn-

I think that I have to cover some general information prior to getting to specific questions.

Dr. Dodds has written extensively on hypothyroidism and the hypothesis that vaccinations are causing immune mediated diseases but has not done research that verifies these claims or based these claims on scientifically valid studies from other researchers. I have spoken directly with Dr. Dodds about this. I felt it necessary to do that, because she had a strong reputation as a scientist due to her early research work. She told me that sometimes it is necessary to act more quickly than is possible through scientifically sound research and that she feels strongly that her claims will eventually be proven. While it is possible that she may be correct in her assumptions about either the prevalence of hypothyroidism and its undocumented effects or the problems she sees in vaccinations it is important to understand that at this point the claims are unsubstantiated.

Hypothyroidism does have lots of effects that are detrimental, so I am not comfortable calling it a benign condition, either.

Hypothyroidism is difficult to diagnose with certainty at the present time, due to the fact that thyroid stimulating hormone is not readily available anymore. When TSH was available, the "gold standard" for diagnosis of hypothyroidism was the TSH response test. For several years vets struggled to come up with an alternative test and the best of these is the free thyroxine (FT4) by equilibrium dialysis. There is no question that this test is more accurate than other methods of testing for FT4 in dogs. There was a lot of hope that canine TSH (cTSH) testing would be highly accurate, since this TSH testing in humans has proven very beneficial in diagnosing hypothyroidism. However, this just hasn't worked out. Despite this, a lower than normal FT4 combined with a higher than normal cTSH comes very close to being a certain diagnostic test for hypothyroidism.

You are correct that nonthyroidal illness causes a decrease in both total thyroxine (TT4) and free thyroxine (FT4), although the effect on FT4 is less. Due to this, it is important to try to be sure that another illness is not present. Obviously, this can be difficult when you are looking for a cause of subtle changes such as cold sensitivity. I can not say with certainty that supplementation of thyroxine would not be advantageous for patients with low thyroxine levels due to nonthyroidal illness since I am not aware of studies that support or refute this hypothesis. Subjectively, I think that patients who don't really have hypothyroidism do often experience some benefit from the therapy, at least in the short term. I don't think that justifies using a medication that isn't necessary for the life of a patient, though, so I still think accurate testing is best.

I know endocrinologists who have stated at continuing education seminars that a clinical trial of thyroxine is a reasonable approach when the diagnosis of the condition is unclear. This was especially true during the period between the loss of TSH response testing and the availability of FT4 by equilibrium dialysis. You have to have something that you can really judge the response by, though. So the best cases for this approach are dogs that have hair loss or some other symptom that will allow a good evaluation of response to therapy. Based on your note, I can't tell how you would know if the therapy had been helpful.

This is the part of the note that will probably disappoint you, but I don't think that you can tell from the lab work whether hypothyroidism is present, or not. I lean towards thinking it is not a problem but I would push for an equilibrium dialysis test at this time. I can send a list of references to support this if you want, but I would have to do that from home and I am on the road again, so you'll have to remind me. It looks like your vet has been sending the lab work to Michigan State University (or someplace sending the blood to them) based on the reports. MSU has a "premium" (or something like that) panel that includes the free T4 by equilibrium dialysis test and the cTSH test. So there wouldn't be a need to change labs to get the newer testing procedures.

There are two forms of hypothyroidism in dogs. In one form, the immune system attacks the thyroid gland (autoimmune or lymphocytic thyroiditis) and a second form in which the gland seems to atrophy for other reasons. Many more dogs have lymphocytic thyroiditis, measured by the presence of auto antibodies to T3 and T4, than have hypothyroidism. It takes a long time for the antibodies to cause enough damage to cause hypothyroidism and some dogs with lymphocytic thyroiditis never develop hypothyroidism that can be demonstrated through testing.

I would be really surprised -- really really surprised --- if the lameness had anything to do with hypothyroidism. If this is a problem with luxating patellas the best solution is probably surgical repair. If you wish to continue to try medical therapy, the recommended dosage of glucosamine is 25mg/lb of body weight per day and chondroitin 20mg/lb of body weight per day. I do not know with certainty if it really makes a difference if it is given with food but it is supposed to aid in the absorption of the ingredients to do that.

I would be surprised, but a little less surprised than with the lameness, if the pigment change on the nose was due to hypothyroidism. I have not seen any pigment changes of the nasal planum that responded to thyroxine administration, even when I was nearly certain the dogs actually had hypothyroidism.

Since the total T4 levels are very low, I think that testing for hypothyroidism using an equilibrium dialysis test is worthwhile but I would probably be reasonably comfortable doing nothing, too. I would prefer that to a clinical trial of thyroxine but lots of vets would go the other way on that call.

I hope that this information is helpful. If I missed something in your question or if you need further clarification of any of the points, please feel free to write back.

Mike Richards, DVM 5/15/2001

Timing of Thyroid medication

Question for you: Kodiak (the 14yr old with Vestibular probs) and now Sunni (7 yr Rot/Beagle cross) are taking thyroid meds. When is the best time to give this? Morning before we leave for work, or evening?

take care, Rob

Answer: Rob-

It is not supposed to matter what time of day thyroxine is given for replacement therapy in dogs. If I understand the theory correctly, dogs have a pretty large reserve pool of thyroxine and the maintenance therapy makes sure that the reserve is adequate for daily needs. It isn't until the reserve is depleted that clinical signs of hypothyroidism occur. Replacement therapy replaces both the reserved amount and meets the circulating need. So when you have reached a stable point in the blood levels of thyroxine, once daily administration will usually work and the timing of it is not critical. So the best time really comes down to the time that is most convenient for you.

Mike Richards, DVM 12/10/2000

Thyroid and Allergy problems in Golden - Allergy tests - thyroid tests - keflex

Question: I have a 7 year old, spayed golden retriever. She has always bitten and scratched herself excessively. The summer she was 3 it was so bad, her intire neck / chest area was totally raw and looked like an open sore. I switched her flea med. from Program to Advantage and she made a complete recovery. She still scratches and bites a lot, just not quite as bad as she used to. She started chewing her tail and back really bad at the beginning of the summer (this year) and my vet gave her a cortisone shot and it helped for a couple of months, but now that the shot has worn off, she's at it again. Since then she has also developed an ear infection (not uncommon). When I took her in to get an antibiotic for her ears, we talked about really getting to the root of the problem. He thinks the ear infection and skin problem are related. He prescribed Otibiotic ointment for her ears and an internal antibiotic called Keflex (500mg / capsule to be taken twice daily for 40 days), gave her another shot of cortisone and also a very strict diet of Iams Eukanuba Response FP formulated for skin and coat. His theory was this was allergies (my thought, too) and we'd give her the antibiotics to clear up the skin and restrict her diet to rule out a food allergy. But here's where I get confused... He also ran a T4 test to eliminate the possibility of thyroid malfunction despite the fact she weighs 74 lbs. She's perfect in weight and size. She's very fit and thin, long legged, and beautiful. The next morning he called me with the results of the T4 test and said she was .7 (whatever that means) and wants to begin lifelong treatment for hyper-thyroid. I think he's a great vet, but sometimes a fast talker (like a car salesman) and a little too excited about prescribing multiple meds. She currently takes Advantage for fleas and Interceptor for heartworm prevention every month. My questions are...

1. What can you tell me about Keflex ? On the side of the capsule is printed Z4074 .Is it supposed to have a strong odor ? Does she really need such a strong dosage ?

2. Explain the thyroid test and it's result in my case. Are there any other tests to back up the T4's result ? How accurate is this test ? What factors would cause an incorrect diagnosis from the T4, such as other meds she's on or what she had eaten recently ? If I do medicate her for this, what are the side effects especially long term on liver and kidneys ?

3. What are the different kinds of allergy tests available ? Would I need to go anywhere special or can my local vet administer them ? How accurate are they ?

4. What is your best hypothesis and opinion on coarse of treatment ?

Thank You, Amy

Answer: Amy-

I'll try to answer your questions in order, as much as is possible.

Cephalexin (Keflex Rx) is usually dosed at 10mg/lb of body weight for skin disease. So the dosage is actually low but since there isn't a 750mg capsule, it is not uncommon for vets to use 500mg twice a day up to about 75 lbs of body weight and then 1000mg twice a day for weights between 75 lbs and 100lbs. I just tend to use the 500mg dose three times a day or give 1 500mg and 1 250mg capsule every 12 hours but I am not sure that it is necessary to stick exactly to the dosage. In any case, the dose is actually lower than normal, not higher.

A total T4 test is an inaccurate method of determining if hypothyroidism is present, unless it is very low. There should be a laboratory normal value, which varies from lab to lab, for this test result. In general, I am not comfortable using a total T4 value to establish the presence of hypothyroidism unless the value is something like 0.1 ug/dl, although values of less than 0.5ug/dl are very suspicious for the presence of hypothyroidism in a dog that has no other systemic illness. It is really important to realize that a concurrent illness, such as severe skin infection, can lead to suppressed total T4 values.

Currently, the most accurate test for determining whether hypothyroidism is present is the free thyroxine (Free T4, FT4) test done by equilibrium dialysis. This test is available through Michigan State University's endocrine lab and probably several commercial labs, as well. When combined with measurement of canine thyroid stimulating hormone (cTSH) it is slightly more accurate, but not enough to make it absolutely necessary to run both tests. A low free T4 combined with a high cTSH level is a very sure sign of hypothyroidism. The free T4 test is also affected by systemic illnesses. The free T4 level is suppressed by the presence of another illness, so this has to be taken into account when interpreting this test. It may be better to clear up as much of the skin disease as is possible and then retest, using the free T4 test by equilibrium dialysis as the testing method. Your vet may feel that the clinical signs and low total T4 test are enough to diagnose this condition but you are looking at a disease that requires lifelong supplementation so I think it is best to be as certain of the diagnosis as is possible.

One reason that veterinarians are willing to supplement thyroid hormone based on the clinical signs and/or total T4 testing is that thyroid hormone supplementation causes very little problem in dogs that do not require the medication. Dogs tolerate administration of thyroxine, even when they don't need it, very well. I can only remember one dog that had any problems as the result of thyroxine supplementation and that dog was just very excitable and restless. Both symptoms resolved when the medication was withdrawn. That still doesn't justify using a medication when it is not needed, though.

The best allergy test is intradermal skin testing, which is usually done by a veterinary dermatologist, although there are a number of general practitioners who do this test, as well. As long as the person doing the testing is experienced, there should be no problem with using a general practitioner's services. It is possible to test for inhalant allergies using blood testing but this is not yet considered to be as accurate as skin testing. It is getting pretty close, though. We have done a small amount of blood testing for allergies, mostly for clients who refused to go to a dermatologist, and we have had reasonable success with the testing. I would still take my dog to a dermatologist for skin testing, though. The only way to measure accuracy is by response to treatment with hyposensitizing agents, which may fail for reasons other than test accuracy. However, skin testing usually results in about 70 to 80% success rate for hyposensitization and serum testing about a 60 to 70% success rate.

In the mid-Atlantic region, I think that all skin disease should be considered to be linked to flea bites, flea allergy and inhalant allergies until proven otherwise.

Mike Richards, DVM 10/18/2000

Thyroid hormone and breeding in Labrador

Qustion: Dr. Mike,

I was wondering if you got my e-mail of 8/25/00 asking if there was such a thing as an antigen that attacks and kills the male sperm? My 6 1/2 choc. Lab. and now her 3 1/2 yr.old daughter both have had only one litter of pups and has not been able to conceive since.

But now I have spoken with a man that deals in animal husbandry, and I showed him the thyroid report on my 3 1/2 yr. old and he says her numbers are fine for a pet, but for breeding stock-no good. Now my question becomes-is there a quick way to find out what hormone(s) she is lacking, and can she be cured. And what about breeding her with a male whose thyroid counts are very high, could we be assured that the litter will have good thyroids (providing, of course we can get her pregnant again)?

Thanks, Kathy Answer: Kathy-

The best I can do for you is to try to explain what thyroid tests are available and what they might mean.

The most accurate test, at the current time, for hypothyroidism is the free thyroxine (f T4) test, measured by equilibrium dialysis. It is important that it be measured in this manner for best accuracy. If the free T4 level is low, there is over a 90% chance that the dog is actually hypothyroid. This value can drop in response to severe or chronic illness from other causes but it less likely to be affected in this manner than the total thyroxine (TT4) test that is more commonly run.

It is now possible to measure canine thyroid stimulating hormone (cTSH), a test that it was hoped would clear up any ambiguity about thyroid test results in dogs. It hasn't worked as well as hoped, but a high cTSH level combined with a low fT4 level is very strongly supportive of hypothyroidism.

The total thyroxine (TT4) test is a good screening test because dogs with total thyroxine levels in the upper half of the normal range are very unlikely to have hypothyroidism and dogs with TT4 levels well below normal are very likely to have it. High normal or higher than normal T4 levels can occur if there are antibodies against thyroxine present in the dog's serum.

The total triiodothyronine (T3) value may rise to higher than normal levels in dogs that are producing antibodies against T3 and T4. Other than this finding, T3 values don't appear to e very helpful in diagnosing hypothyroidism in dogs. The production of antibodies against thyroid hormone would logically relate to the development of hypothyroidism but this isn't reliably the case. It is a good indication to continue to look for problems, though.

It is possible to test for antibody production against T3 and T4 (T3AA and T4AA) and this is part of the standard thyroid panel from Michigan State and probably some other laboratories. At the present time, I do not know exactly what the presence of auto-antibodies against these hormones really means. There is some speculation, especially in golden retrievers and dobermans, at least anecdotally, that high levels of T3AA and T4AA in a young dog indicate a higher tendency to develop hypothyroidism later. This has not been proven, to the best of my knowledge, but these breeds have high tendencies to have antibodies against thyroid hormones and also have higher than average incidence of hypothyroidism.

So I am not sure what to make of the advice that you have received. If this dog has a low fT4 value, or particularly a low fT4 combined with a high cTSH value, then I would think that she is very likely to be hypothyroid. If this is not the case, I do not think that it is currently possible to be sure that she will one day be hypothyroid, nor to predict whether her offspring would be hypothyroid.

Michigan State University's lab has a thyroid panel available that includes measurement of the free T4 by equilibrium dialysis. It is not their standard panel, if I remember correctly. This is one source of an accurate way to determine if hypothyroidism is likely.

It is not possible to cure hypothyroidism. Like diabetes and other hormonal diseases, it is a disorder that is managed by lifelong replacement therapy for the missing hormone. Due to the fact that this is a lifelong problem, it is important to be sure that the diagnosis is accurate, so it is worth going to some trouble to get an accurate diagnosis.

I do not know the hereditability of hypothyroidism in Labs, but it is a concern when supplementation of thyroid hormone makes it possible for an affected dog to become pregnant and carry puppies to term, since there is a chance of passing on the trait. This has to be considered when making decisions about breeding a dog known to have hypothyroidism.

I hope that this clears things up some. If you are getting a different explanation of the meaning of these hormones from someone else I would like to hear what they are saying so that I could research it some.

Mike Richards, DVM 9/7/2000

Medication dosage and T4 levels - German Shepherd

Question: Dr. Richards,

I emailed you several weeks ago regarding our German Shepherd. She had been limping, unable to walk for long distances etc. It turns out she has arthritis in her elbows combined with a low thyroid. In less than a week of thyroid medication her energy level climbed off the charts. Her slight overweight problem is also becoming less of a problem.

Is the dogs thyroid level was 5.4 which I understand is a little high. Is there a thyroid suppliment that can be given once a day? Your assistance is appreciated. Dale

Answer: Dale-

A thyroid level of 5.4 is pretty high for a dog. If this value is from blood drawn around eight hours after the morning pill, which should be about the lowest serum level, it may be necessary to lower the dosage. We usually use thyroxine on a twice daily basis for a month to two months, and then once daily after that. In dogs, there is a large reservoir of T4 in the tissues and once this supply is replenished it is reasonable to supplement once daily instead of twice daily, unless serum levels fall below normal levels again as serum levels are checked on a routine basis.

Mike Richards, DVM 8/10/2000

what is the average T4 level

Question: I do not know what the normal T4 level is for dogs. This German Shepherd weighs about 110 lbs which is now continuing to drop thanks to increased activity. Rimadyl did not have a good response, however, that was before the thyroid deficiency was diagnosed. Your assistance is appreciated. dg

Answer: DG-

There are two different units that thyroxine (T4) is reported in. Every lab has different normal values and it is important to use the established normals for the lab that the blood is drawn from. A general average of these levels probably would come close to:

Canine T4 normal (ug/dl) 0.8 to 3.9 (nmol/L) 15 to 50 (from Michigan State University's lab)

Usually, it is best to be in the upper half of the normal range, but not to exceed it.

Mike Richards, DVM 8/4/2000

Hypothyroidism in a greyhound questionable

Question: Dear Dr. Mike,

I have a 3 year old Greyhound who is currently taking .8 mg of thyroxin (twice a day). This is his first month on that dosage. He weighs 77 lbs. The reason I had him tested for hypothyroidism was because he is a Greyhound and he would have reverse sneezing attacks about 3 times a day. His thyroid level came back "low normal" but because of the reverse sneezing he was started on .3 mg twice a day. However, every time he is on the same dosage for more than 2 months the reverse sneezing starts up again. When the dosage is increase by .1 mg, the sneezing stops. He is now, with the .8 dosage, at the recommended level - even though he still tests "low normal". If he starts having reverse sneezing attacks again at this level should we continue to increase the dosage? His attacks are very violent. Also, I have heard that Soloxin is the preferred thyroid medication for Greyhounds - do you believe this to be true?

Thanks for any help.


Answer: Linda-

I would tend to be a little suspicious of a diagnosis of hypothyroidism in a greyhound. This breed is reported to have total T4 levels and free T4 levels about half of what is considered to be "normal" for other dog breeds. This makes it very easy to misdiagnose hypothyroidism in this particular breed.

I know of no correlation between reverse sneezing and hypothyroidism, but there are lots of things that I don't know, so I can't rule it out. The response you are seeing does seem to support a link, though.

Soloxine Rx, the "brand name" thyroxine, does sometimes seem to work better than generic thyroxines, in all breeds. I don't know if greyhounds have even more trouble than other breeds with the generic brands, or not.

It may take up to two months for thyroid levels to stabilize after administration of thyroxine, so if you want to retest, it is best to wait a couple of months after discontinuing the thyroxine administration.

Greyhounds are pretty prone to periodontal disease and that is sometimes worse in dogs with hypothyroidism. Periodontal disease is sometimes implicated as a cause of reverse sneezing but all of that still makes a pretty weak link between reverse sneezing and hypothyroidism. It was the best I could come up with researching this, though. Again, that doesn't mean that your vet doesn't know something that I don't.

I don't know of a consistently effective therapy for paroxysmal respiration (reverse sneezing). However, I also have not ever known of a dog that died as a result of this problem. We did have a Boston terrier and a pug in the practice who I worried might die. One of them responded pretty well to steroids from an inhaler when the attacks would occur but the other one didn't.

I wish I could help more with this.

Mike Richards, DVM 2/15/2000

Hypothyroidism - canine

Q: my Schepperkee is 7 yrs old , 15 lbs has been diagnoised with hypothyriodism. he has been on soloxine 0.1mg 2x a day. he started taking 8/24/98 he has to go back in in a month. They will see if this is the correct dosage and type . I have noticed he does not want to go up stairs or jump on the bed. I not sure if it is the medication or side effects . If you have any knowledge of hypothyroidism you could share with. me i would really appreciate the information . Should his joints be stiff?

A: Dear Amy-

Hypothyroidism is the most commonly diagnosed hormonal disorder in dogs. It is also probably the hormonal disease diagnosed in error most frequently. The best method of diagnosing this condition is the use of a test known as the "free T4 by equilibrium dialysis" or "FT4ed". Combining that test with a canine thyroid stimulating hormone (cTSH) test is a little more accurate than either test alone. These tests are not the most commonly used tests for this condition at the present time so it might be worth checking to see what test was used to confirm the diagnosis of hypothyroidism. Even in dogs in which the tests indicate a high likelihood of this disease it is important to monitor response to treatment as an additional method of confirming that the problem exists. So you need to pay attention during the next 60 to 90 days and to be as objective as possible about whether or not the medication is helping.

Hypothyroidism has been associated with muscle pain and poor muscle function. It has also been associated with neuropathies (nerve damage) that could also lead to the appearance of stiffness or lameness. These aren't the most common signs seen with hypothyroidism but there have been some cases in which lameness or leg pain were the only clinical signs of hypothyroidism. (reported by Budsberg, et al, 1993 AVMA Journal). Another possibility with muscle pain and muscle weakness is hypoadrenocorticism (Addison's disease). If the muscle weakness got worse when the replacement hormone (levothyroxine, Soloxine Rx) was started it might be a good idea to consider checking for this hormonal disease as well.

Usually levothyroxine has minimal side effects but it can cause signs associated with hyperthyroidism, such as increased appetite, rapid heart rates, increased activity levels, nervousness and fever if it is overdosed. The dose you are giving is low enough that overdosage seems unlikely, though. The dose is approximately 0.01mg/lb once or twice a day -- so this would be .17mg to .34mg per day, right in the dose range you are giving (.2mg/day). Most of the time it is possible to give this medication to a dog that doesn't have hypothyroidism without causing noticeable side effects except perhaps a better haircoat.

There are a lot of things that might cause a decrease in jumping or climbing activity in addition to hypothyroidism and hypoadrenocorticism, though. Spinal disc disease, luxating patellas, cruciate ligament disease, degenerative joint diseases, tick-borne infections such as Lyme disease or Rocky Mountain Spotted Fever can all lead to these signs. In addition, dogs get muscle strains, joint strains and sprains assorted other injuries.

If this problem only showed up after administration of the levothyroxine it is important to call your vet and set up a recheck exam since it is possible that there is a second problem. If the problem was present before the diagnosis of hypothyroidism it would be important to report whether or not administration of the replacement hormone is helping and then to follow your vet's advice about when to have a recheck done for that particular problem. I'd ask about how the hypothyroidism was diagnosed, too. Just in case you missed it, there is more information on the testing in one of the recent VetInfo Digests.

Mike Richards, DVM

Older dog - Hypothyroidism

Q: We did a geriatric panel and it was fairly normal with the following exceptions: Alkaline phosphatase: 156 (H), AST: 21 (L), Cholesterol: 391 (H), and Lipase: 652 (H). The vet suspects A-Typical Cushings. He was on & off prednisone for years for flea-bite allergies & then the hip problems. I will be taking him to a cardiologist in a few weeks to get a better fix on what's going on with his heart & lungs, but was hoping you could give me some information on the blood work results & what A-Typical Cushings is (I've looked up Cushing Syndrome, but the symptoms don't fit my dog at all). Thank you, Mary

A: High cholesterol levels seem to correlate pretty well with hypothyroidism. It might be worthwhile to run just a little more labwork and check for this, too. Going to see the cardiologist is probably a good idea, too.

Mike Richards DVM

Hypothyroidism or not- Itchy dog

Q: Dr. Mike, My three year old dog, Emma has had an itching problem for about two years. The vets have prescribed Prednisone, Cephalexin, Amitripylline, and many other mediations and remedies that have not worked. The Prednisone caused her to have so many urination accidents it practically ruined our carpet. Her diet consists of Iams Low Active and Iams Canned Low Active dog food. Her skin has a symmetrical pattern of hair loss and black pigmentation of the skin. It appears on her fore legs, back legs, and the sides of her body. She is constantly scratching and also rubbing her nose. Does she have Hyperthyroidism? What else could it be? We bath her in the Episoothe Oatmeal Shampoo and apply the same conditioner, but it doesn't really seem to help her. Awaiting your advice, Donna

A: Donna- It is possible, but not very likely, that Emma could have hypothyroidism (too low a level of thyroid hormone in the body). It is unusual for dogs to have high thyroid levels (hyperthyroidism), which is more common in cats. Low thyroid hormone levels can lead to chronic skin disease but usually this affects dogs slightly older than yours.

The most economical thing to do for the long run may be to ask for referral to a veterinary dermatologist. Specialists tend to see the chronic and odd cases, so often recognize unusual syndromes a general practitioner may miss. If this is not possible, allergy testing and perhaps even skin biopsies may be helpful. Not all dogs with allergies respond well to prednisone. Flea control is almost always indicated in itchy dogs, even if no fleas at all are seen. It is amazing how often it helps even when fleas do not seem to be the problem. Using one of the new flea products, Frontline (Rx), Advantage (Rx) or Program (Rx) could make a big dent in the expense.

Good luck with this. Most skin problems can be controlled if a diagnosis can be made.

Mike Richards DVM


Michael Richards, D.V.M. co-owns a small animal general veterinary practice in rural tidewater Virginia. Dr. Richards graduated from Iowa State University's College of Veterinary Medicine in 1979, and has been in private practice ever since. Dr. Richards has been the director of the PetCare Forum...