The information contained in this sticky is provided for educational purposes only and is not intended to replace veterinary advice. The intention of this sticky is to open doors to understanding about the specific medical condition or topic, allowing for educated and on-going discussion with your vet.
 Cooky Angel, achieved OTJ status in spite of HT |
Diabetic Cat Care
Hyperthyroidism 101 |
There's no doubt, the mix of feline diabetes along with a diagnosis of Hyperthyroidism complicates matters; increasing the challenges faced when it comes to achieving good regulation and the potential of OTJ status, however, it is not impossible. Cooky did it!
If you read nothing else, please pay attention to the advice in bold font in this introductory section.
HT is diagnosed at the time blood work is done; typically the test for HT is not included in a general CBC (complete blood count), however a Senior Wellness panel usually includes the primary test for HT which is called a T4. When you take your cats to the vet's for their annual lab work, it is wise to ask the vet to request the lab hold the blood samples for possible further testing once the T4 value is known. It's less costly (and less stressful) to ask them to hold the sample compared to having to take your cat back for a second vet visit and blood draw. If the T4 comes back raised, then the lab already has the blood sample, and requesting an additional test - the Free T4 - is recommended to further help to confirm or deny a diagnosis of HT. Please note, the test is called a Free T4 but the test is NOT free!
When it comes to testing for Hyperthyroidism lab work is not fool-proof; so assuming the T4 comes back elevated, PRIOR to starting your cat on any HT medications, it is best to follow through with all three tests in the series (and if at all possible the technium scan) to confirm or deny HT. It has been the case numerous times where both the T4 and Free T4 test results have come back with higher than normal values and a confirmed diagnosis of HT has been made, but it is in fact ANOTHER health issue in play which has skewed the lab results rendering a false-positive diagnosis.
To firmly confirm or deny a diagnosis of HT, there's
a third test required which is known as the
T3 suppression test.
The three tests in the series are the T4, Free T4 and T3 Suppression test -
results should be studied in
conjunction with each other as other (far less
significant) health issues can
(and do) skew individual
HT test
results.
The veterinary community at large are not aware of this for the most part, trusting that the T4 and/or Free T4 alone are sufficient to confirm a diagnosis of HT. Please, do not put your cat in the position where short cuts are taken, or trust is placed on misunderstanding or lack of knowledge rather than fact. Doing so could result in loss of life. IT is much better to be safe than sorry.
The disease itself
seriously affects the metabolism - the medications required to treat HT are very
potent - affecting the heart and the kidneys and can take their toll on the
entire body - potential outcomes when there's no treatment, or there's been a
misdiagnosis and medications have been given when not needed are not limited to
heart attack, stroke, total kidney failure, and/or worse. It is STRONGLY
advised to follow through with all three tests to ensure an absolute
confirmation of HT prior to starting any medications which could inadvertently
be life-threatening. Stopping HT medications is just as dangerous - when the
drug is stopped it can cause a sudden crash in the cat's health. This has
nothing to do with being diabetic and everything to do with being misdiagnosed
and put on medications for HT inaccurately. That said, if your cat is truly
Hyperthyroid, they WILL need medication (surgery or radio-iodine) -
otherwise they will not survive.
Lastly, while this may be very blunt, if for whatever reasons you determine you cannot deal with your cat's confirmed diagnosis of HT (or FD for that matter) please - do not allow them to suffer which they most certainly will without treatment....there are other options available, whether that is giving your cat to someone who will be able to care for them, or by doing the humane thing - putting your cat down. It's one thing not to know what the outcome might be if either disease isn't treated, but if you're reading this far into this sticky and the website, it is now impossible to claim there was no understanding your cat would suffer tremendously without treatment.
What is Hyperthyroidism?
Cats who are hyperthyroid have too much
of the hormone thyroid in their system causing
over activity in the thyroid gland;
the result is
their metabolism
operates far too fast or “hot”.
Feline
Hyperthyroidism
is one of the most common hormonal diseases seen in older cats. It
generally occurs in cats over 12 years of age, but can happen in younger cats
too (7 years of age and upwards). It is very rarely seen in cats younger
than 7 years of age.
What are the symptoms
of HT?
Just like with humans, the thyroid for cats is
located in the neck area, your vet can show you where it's located and you'll be
able to feel it.
When a cat has hyperthyroidism either one
or both of the thyroid lobes become enlarged (both lobes are affected in 70% of
cases). This leads to excessive production of the thyroid hormones T4 (aka
thyroxine) and T3 (aka tri-iodothyronine).
Common symptoms:
-unexplained weight loss is often the first indicator of the disease.
-ravenous appetite
-Increased water intake
-Increased heart rate - the high
metabolic rate will cause the heart to beat much faster than normal.
Normally for cats, their heart rate is approximately 180 beats per minute; a cat
with hyperthyroidism will often have a heart rate of over 250 beats per minute.
-Vomiting and diarrhea - the intestinal
system is forced to move very fast due to the cats increased metabolic rate.
Cats will often vomit, generally soon after
eating, and
diarrhea is also
common because food moves through the gut too quickly to be digested properly.
-Palpable thyroid gland - vets and
sometimes owners too, can often feel the enlarged
thyroid gland in the cats’
neck.
-Poor coat condition - cats will often
have dull and unkempt coats. This is due both to their general ill health,
and the fact that they will often stop grooming themselves properly.
-Anxious expression - vets will often
describe cats as 'looking Hyperthyroid’; this is due to the wide eyed and
anxious expression affected animals often have.
-Seeking out cool spots - affected cats
will be noticeably intolerant of heat and seek out cooler places.
Many of these signs can be subtle at
first (and are also common with other health
issues); they
become more severe as the disease progresses.
What is the Thyroid and why is it
so
important?
The thyroid is a two-lobed gland located in
the neck of people, dogs, cats, and other animals. There is one lobe on each
side of the wind pipe.
The hormone produced by the thyroid gland is essential for the normal growth of the skeleton and brain in young animals. The thyroid is linked to metabolism, heart rate, breakdown of fatty tissues, digestion, and red blood cell production.
How is
HT
diagnosed?
A thorough physical exam will generally
identify one or
both
enlarged thyroid glands, often felt as a small, firm mass
in the neck (these are often about the size of a pea or a baked-bean in
hyperthyroid cats) although it is not uncommon for there to be no palpable mass.
Because
thyroid hormone levels fluctuate throughout the day, it may be
early in the course of the disease, or
if other health issues are present, the
standard T4 or Free T4 test results can be skewed. Most vets
believe the Free T4 by equilibrium dialysis (fT4ED) is
the most accurate way to measure fT4 and is more sensitive in assessing thyroid
function in sick animals where the T4 may be depressed.
However, it is important to understand both tests can give false results if
there are other health issues in play.
The best way to confirm a diagnosis
of HT, “without a doubt”, is to have a T4, Free T4 AND the T3 suppression test
performed and, if possible to have a Technicum scan done. In a
cat without HT, the administration of T3 orally (usually at home
by the owner) will cause the
T4 levels to decrease, in a hyperthyroid cat they will not decrease or will only
decrease very slightly.
Your vet may also recommend a
thyroid scan for
your cat which will likely need to be undertaken at a vet school/hospital or
other specialized clinic. If your vet does not recommend a Technicum scan,
it is recommended to ask for it to be done,
and it should ALWAYS be done prior to the I-1131 radiation treatment to cure HT
to prevent over dosing of radiation resulting in the cat becoming HypO-thyroid.
Since most cats with hyperthyroidism are
older, it is recommended that your cat has other blood tests to assess their
organ function and make sure that they do not suffer from any other problems,
particularly
when it comes to the kidneys. This is important because other conditions might
affect the successful treatment of hyperthyroidism
and as well, the HT (and medications) can mask underlying CRD.
Dr. H - DVM
08/10/2008 :
Free T4 fluctuates
within the cat more than TT4 does over the course of any time period, so this is
also an issue. I have found that either TT4 alone (if the number is above
2.4-2.5 in an older cat) or serial TT4 (2 tests at least 2-6 months apart),
coupled with clinical signs, is the most reliable lab test for HyperT outside of
the Technicum scan....
How is Hyperthyroidism treated?
There are three main ways of treating hyperthyroidism;
drugs, surgery or radiotherapy. Of the three forms of treatment
available, radioactive iodine treatment (the I-1131) is the
only treatment which totally cures the hyperthyroid
state. Surgery is second when it comes to curing the disease; however, it
is only possible when all off the thyroid is removed. Drug therapy is
on-going for life and requires close monitoring. While the I-1131 is expensive,
compared to surgery or the on-going medications which will be required
to treat HT over the course of your cat's life,
depending on other health issues, the I-1131 is more cost effective in the long run.
Radio-active
Iodine Treatment (I-131):
Radio-iodine therapy is the treatment of choice for feline Hyperthyroidism. It is the safest, most specific treatment available, and has an excellent cure rate (>90%). It is a particularly useful treatment for cats with bilateral thyroid involvement (approximately 80% of cats), cats with ectopic (noncervical) thyroid tissue, and the rare patient with thyroid carcinoma. No side-effects are seen from the radiation therapy per se, and the treatment is typically well-tolerated by even the most debilitated, elderly hyperthyroid cat. When patients are pretreated with thioureylene drugs and selected carefully, the risk of unmasking preexisting renal disease is minimized. What is somewhat stressful is the fact radio-iodine treatment requires the cat to be kept in isolation for a given amount of time (every center's requirement varies depending on state/country). Many treatment centers now offer web-cam services to HT pet owners so they can check at any time to see how their cat is making out. It's noteworthy to mention, the suggestion will be made to provide a t-shirt or towel with your scent, as well as toys for your cat to help them feel more comfortable in new surroundings - due to the radiation levels, these will not be returned on release.
Radio-iodine therapy is very specific because
the thyroid glands are the only tissues in the body that concentrate plasma
iodine actively. The glands cannot differentiate between normal dietary iodine
(stable iodine) and the
radio-active iodine used for therapy.
Radio-iodine
is concentrated by the active (adenomatous, or rarely, carcinomatous) thyroid
tissue, which is destroyed in the procedure. The normal thyroid tissue is atrophied in the
hyperthyroid cat due to lack of stimulation by thyroid-stimulating hormone,
it does not accumulate radio-iodine, and
as a result is spared. After radio-iodine
therapy, cats typically experience a period of subclinical hypOthyroidism
which is almost
always asymptomatic and does not require therapy in the vast majority of cats.
During this period, thyroid-stimulating hormone secretion resumes, the atrophied
thyroid tissue becomes functional again, and the cat then becomes euthyroid (normal
thyroid gland function)
permanently.
The benefits of
radio-iodine
treatment include:
-it is an
extremely effective form of treatment
-it resolves hyperthyroidism quickly
-it requires no anesthesia
-no pills or gels are necessary
-it rarely causes
hypothyroidism
(but it can which will require drugs to deal with)
The negative aspects of I-1311 treatment are that sophisticated facilities licensed for use of radio-active materials are required. Although this treatment is not available world-wide, more treatment centers continue to open. It tends to be more expensive than surgery, in part because cats treated with radio-iodine must remain hospitalized until their levels of radio-activity drop to safe levels. Cats can be required to stay at the centers for a period of several days to a week , or possibly longer. When the cat returns home, precautions are required to be taken to avoid transfer of radioactivity, for example; stool and urine must be collected from the litter box and stored in a contained location for a period of time before disposal. Minimum physical contact with the cat is required (the use of gloves is recommended); keeping the animal away from pregnant women and young children is imperative.
It is absolutely required to make certain any facility will provide an FD cat with regular insulin shots, ideally with BG monitoring taking place while in clinic for an I-1131 treatment. Many facilities will not test BG due to concerns over workplace safety. If it is the case you are not able to find a facility which will do the testing, they will only give insulin shots - please post on forum well in advance of scheduled treatment as experienced members will be able to assist to come up with a plan for blind-dosing amounts to keep your cat as safe as possible (from ketone production and DKA) and in relatively good numbers while the cat is in quarantine.
Blunt the Worsening of Azotemia After Radio-Iodine Treatment
Transient HypO-Thyroidism after Radio-Iodine Treatment
Please note, prior to the I-1131, it is recommended to have a trial run of the drugs (Methimazole) in order to ensure there are no underlying kidney issues as it's very important to know and understand whether the kidneys are damaged prior to the procedure.
Surgery:
Surgery can be used to remove the
abnormal thyroid lobe or lobes. The downside of this surgery is that it does
require anesthesia and the possibility that the entire thyroid is not removed.
Many cats suffer from heart, liver and intestinal changes
associated with hyperthyroidism which creates more of a surgical/anesthetic risk.
The most common complication of surgical
thyroidectomy is hypocalcemia as a result of inadvertent damage to the
parathyroid glands or their blood supply resulting in
hyperparathyroidism.
A 10% fatality rate has been associated with thyroid surgery so it is wise to fully research the surgical option before making a final decision.
Drug therapy:
The most common error made when treating Hyperthyroidism with drugs is that most cats are started off on too high a prescribed dose. The drugs act by reducing the production and release of thyroid hormone from the thyroid gland.
It is noteworthy to mention, HT drugs can cause
anemia or gastrointestinal upset; there is less risk of these conditions with
transdermal gels but it is important to discuss all potential options and risks
with your vet.
There are
different
forms available:
Methimazole (Felimazole; Dechra, Tapizole (generic)
Methimazole is specifically licensed for treatment of feline hyperthyroidism both in the USA and Europe in 2.5 mg and 5-mg tablets. (Commonly prescribed is Felimazole, Dechra Veterinary Products – which should be avoided for FD cats as it is sugar-coated). Methimazole is administered twice daily, typically cats are started out on too high a dose, and rather than the 2.5 mg or higher dose typically prescribed by the vet, the Yahoo Feline HT Group recommends a starting dose of 1.25mg. Close monitoring of how a lowered dose is working is highly suggested.
Dr. H - DVM :
11/11/2007 :
Carbimazole
Tablets (Controlled-Release)
A controlled-release formulation of carbimazole (Vidalta,
Intervet Schering Plough) is licensed for cats in Europe for once daily
administration. This formulation is not available in the USA.
Administration of this drug with food significantly enhances its absorption.
It is important to note there are
reports of consistent overdose on HT specific forums when using Vidalta.
Transdermal
Gel
Carbimazole and methimazole
can be formulated by most veterinary
or human compounding pharmacies. It is applied to the
non-haired inner portion of a cat’s ear for transdermal administration.
Such custom formulation increases expense of therapy and the stability of the
product can never be guaranteed. To prevent absorption of the drug through
one's own skin, it is best to wear gloves or a finger cot for application, and
wash your hands afterwards. One advantage of using a compounded formulation of
methimazole (or carbimazole) over the 2.5- or 5-mg tablets is that it is easier
to make smaller or finer dose adjustments.
Transdermal administration is
associated with fewer gastrointestinal side effects than the oral route, but
some cats resent manipulation of their ears and crusting can occur between doses
leading to redness of the skin. These problems can usually be prevented by
removing any crusted material and cleaning the ear flap prior to administration.
The drugs work by neutralizing the excess
thyroid hormone once it has been released by the thyroid gland, they have no
effect on the over-active gland itself. Thyroid hormone concentrations
usually fall back to within the reference range within 3 weeks.
There is a good amount of
detailed information on
HT testing
online, as well as information about
measuring
T4, the
T3 Suppression test and
general information about
Thyroid
Scans:
Follow Up
After surgery, radiation or once drug therapy starts,
cats should be reassessed
after 3
to 4
weeks
with a serum total T4 concentration measured. The goal of
medical therapy is to maintain total T4 concentrations within the lower half of
the reference range. Low serum T4 values should be avoided however, because it
has been shown that chronic hypothyroidism is harmful to kidney function and may
worsen already present chronic kidney disease. Treatment is then adjusted
according to response.
Regular follow up blood tests, (approx.
every 3-6 months), should be carried out to monitor the effectiveness of
therapy,
and further urine testing (such as the USG)
to monitor kidney function and to look for potential side effects.
To maintain control of hyperthyroidism,
HT drugs will need to
be given daily for the rest of the cat's life.
For most cats Methimazole and Carbimazole are safe and effective treatments for hyperthyroidism. Side effects are uncommon and if they do occur they are usually mild and reversible. Poor appetite, vomiting and lethargy are the most likely side effects and often resolve after the first few weeks of treatment and/or by temporarily reducing the dose of treatment and administering the tablets with food.
More serious problems,
including reduced white blood cell counts, reduced platelet counts (which help
the blood to clot), liver disorders, or skin irritation are rare, but if they do
occur then an alternative treatment must be used.
When dealing with Hyperthyroidism, and in consideration ECID (every cat is different) it's important to understand the Pros and cons for all three Hyperthyroidism treatment regimes.
Thyroid hormones have effects on
virtually all the organs in the body, and therefore HT sometimes causes
secondary problems.
The effect of thyroid hormones on
the heart is
to stimulate a faster heart rate (more rapid beating of the heart) and a
stronger contraction of the heart muscle. Over time, with hyperthyroidism the
muscle of the largest chamber in the heart (the left ventricle) enlarges and
thickens – so called ‘left ventricular hypertrophy'. If left untreated and
unmanaged, these changes will eventually compromise the normal function of the
heart and can even result in heart failure. This means that in some cats with
hyperthyroidism, additional treatment may be required to control secondary heart
disease. However, once the underlying hyperthyroidism has been controlled, the
cardiac changes will often improve, or may even resolve completely.
Hypertension (high
blood pressure) is another potential
complication of hyperthyroidism and can cause additional damage to several
organs including the eyes, kidneys, heart and brain. If hypertension is
diagnosed along with hyperthyroidism, drugs will be needed to control the blood
pressure to reduce the risk of damaging other organs. As with heart disease,
following successful treatment of the hyperthyroidism, high blood pressure
usually resolves and permanent therapy is not necessary.
Kidney disease (chronic renal failure) does not occur as a direct effect of hyperthyroidism, but the two diseases often occur together because they are both common in older cats. Care is needed where both these conditions are present, as the hyperthyroidism tends to increase the blood supply to the kidneys, which may improve their function but masks underlying renal issues. Blood tests taken regularly to assess kidney function in a hyperthyroid cat may show normal or only mild changes, but potentially more severe renal failure may be masked by the presence of the hyperthyroidism. For this reason, irrespective of what treatment is chosen for long-term management of the hyperthyroidism, it is usually advisable to start on medical treatment (tablets) initially and to monitor the response with repeat blood and urine tests to look at both thyroid and kidney function. On occasion, successful treatment of HT results in a dramatic decline in kidney function. If this is detected it may be necessary to reduce medications so the HT is not fully controlled but renal function is not severely compromised. It's wise to discuss all treatment options, as well as the possibilities with your vet (and the Yahoo HT group) prior to making the decision as to how to best treat the disease in your circumstances.
Fri Nov 20, 2009:
There's no problem with controlling the HT when a cat has kidney issues, you just have to go very slowly and carefully. It is safer to gradually work up to the right dose because eliminating the excess hormone too quickly can cause the cat to crash. Carbimazole is the pre-drug of Methimazole so you can give more than the recommended 1.25mg twice a day starting dose (though kidney cats may have to be started on only 0.625 of Methimazole daily) - I don't know what the recommended dose of Carbimazole is in this situation but they will.
What should I feed a hyperthyroid cat?
Diet and nutritional management is extremely important
for HT cats. As obligate carnivores, cats
are unique in their need for large amounts of dietary protein and low carbs.
This absolute requirement for dietary protein and low carb intake in cats is critically
important when formulating a diet for hyperthyroid cats.
Restoring and preserving any remaining muscle tissue in cats treated for
hyperthyroidism depends upon the cat consuming a diet with sufficient amounts of
high-quality protein. In addition, this recommendation for higher amounts of
dietary protein does not change once euthyroidism has been restored.
A species appropriate diet will help restore and preserve the muscle mass
that has been lost as a result of increased muscle protein breakdown
characteristic of hyperthyroidism.
If your HT cat also has kidney
disease (which occurs in approximately 30% of cases) your vet may recommend a
low protein diet. Dr. H is emphatic this is the wrong way to go
and we agree! Lowering
of phosphate concentration is much more important in management
of HT than dietary
protein restriction, and this can be easily accomplished with phosphate binders
(Aluminum Hydroxide for example) without lowering the protein content of the diet.
The major problem with typical
prescription kidney diets is they restrict protein to the point that some HT
cats metabolize their own muscle mass despite adequate control of the thyroid
condition.
Dr. H points out
in her book,
Your Cat,
since many of our Hyper-T cats have been fed
dry kibble all of their lives; she has
become suspicious of soy, so finding low carb,
high protein wet foods which don't contain soy is suggested.
Quote
from Dr. H's book:
(Soy) is known to have a considerable effect on the human thyroid gland and its addition to cat foods to increase the protein content of those products inexpensively is on the rise today.
Kelp - You will see recipes on
the internet that use kelp. Kelp is very high in iodine and the thyroid gland is
very sensitive to iodine levels that are either too low or too high. Given the
fact that hyperthyroidism is very common in the cat, I do not want to add too
much additional iodine to the diet. Chicken meat (no bones) tends to be low in
iodine but this does not take into account that we are feeding bones with this
recipe. Unfortunately, I have been unable to find iodine levels in whole carcass
chicken or in chicken bones. For that reason, I am adding in a small amount of
iodine to this diet in the form of lite salt (iodized).
**If
using whole carcass rabbit, I suggest calling your supplier and asking if the
thyroid gland is included. If it is, I would not add the iodized lite salt. Be
sure to use all of the blood that comes with any ground food since blood
contains valuable nutrients."
Supplements which help HT Cats
An essential nutrient which plays a big
role when it comes to HT is the B vitamins.
Vitamin B12
and Vitamin B Complex provide healing properties for all cats, especially as
they age, but even more so for FD and/or HT cats. CoQ10 and Milk Thistle
are also very beneficial.
Feline CRF has more
information.
DCC's primary focus is on treating FD using TR, and while we're very knowledgeable about many of the common medical conditions our cats experience, we are not experts when it comes to medical conditions such as HT.
We strongly recommend for more specialized information, or further assistance and support when it comes to Hyperthyroidism, you join the Yahoo Feline HyperT group as they focus solely on the proper management of HT.