Causes of hypothyroidism in cats
In contrast to dogs, where hypothyroidism is one of the most commonly diagnosed hormonal disorders, naturally-occurring hypothyroidism is extremely rare in cats. When it does occur, it is most common in young cats that are born with the disorder.
In older cats, hypothyroidism is usually caused as a complication of treatment for hyperthyroidism. Hypothyroidism may develop after surgically removing a thyroid tumor, destroying it with radioiodine, or by administering antithyroid drugs as a treatment for hyperthyroidism.
Clinical features seen in cats with hypothyroidism
Because deficient thyroid hormone affects the function of all organ systems, the signs of hypothyroidism vary. In cats, signs include lethargy, loss of appetite, hair loss, low body temperature, and occasionally decreased heart rate.
Diagnosing feline hypothyroidism
To accurately diagnose hypothyroidism, one must first closely evaluate the cat’s clinical signs and routine laboratory tests to rule out other diseases that affect thyroid hormone testing.
The veterinarian must confirm the diagnosis using one more specific thyroid function tests. Like dogs with suspected hypothyroidism, these tests may include serum total T4, free T4, or TSH levels.
In some cases, a TSH stimulation test or thyroid imaging (scintigraphy) is necessary for diagnosis.
Treating cats with hypothyroidism
Hypothyroidism is easily treatable; it only requires synthetic thyroid hormone supplements (L-thyroxine or L-T4). The success of treatment can be measured by the amount of improvement in clinical signs. Your veterinarian will have to monitor the thyroid hormone level to determine whether the thyroid hormone supplement dose is correct. Once the dose has been stabilized, thyroid hormone levels are usually checked once or twice a year.
Treatment is generally life-long, but the prognosis is excellent.
30 comments:
Hi there. I have a 3 month old male cat who was just diagnosed with hypothyroidism. He was significantly constipated and it took 3 days of meds and enemas to "clear" him out. He is doing well and has started his thyroid supplements but the vet (who has never treated a cat with the it) says she is worried about his colon functioning properly after being so filled and backed up for so long. I was wondering if you had any experience with that and what your thoughts were. I guess, how well can a kitten's colon "bounce back"? I can't seem to find a vegerinarian in my area who has experience with a kitty like mine. Thanks!!!
Constipation can be a problem in cats with hypothyroidism. I don't know how the diagnosis of hypothyroidism was determined in your cat but kittens generally present as dwarfs and have stunted growth and mental dullness as major signs.
If not done, tell your vet that I recommend a complete thyroid profile (T4, Free T4, T3, and TSH) for diagnosis (see my related blog posts for more information on testing).
Constipation in these cats is controlled routinely with medication (Miralax, lactulose). I like to start with the natural supplement called "slippery elm" and start with 1/4-1/2 capsule in the food each day. That helps for mild constipation.
Thank you so much, they did run the thyroid panel which confirmed it. I am wondering if you think his colon might have irreparable damage from being so filled. I know you haven't seen him obviously...I just didn't know if you had seen kitties whose colon really took a beating, so to speak, and regained its integrity.
Also, will his dwarfism keep him looking like a kitten forever? Will he remain the size he is now?
Sorry if these seem like silly questions, he has just captured our hearts and you are the first person I have found who describes his situation to a tee. Thanks again!
His colon should not be permanently damaged but one bout of severe constipation. It's important that you control that in the future but supplementing with L-T4 should help.
If his bone plates have closed, your cat will not be able to grow any more. If the bone plates are still open, the growth will start again, but he will probably always be small.
Thank you so much Dr. Peterson, I appreciate your feedback!
Hi Dr. Peterson,
I am a CVT and have a 5 year old cat who has a low t4. We discovered it on a pre-surgical work up for a preventative dental. She had been looking unthrifty and "off" to me at home but has had no other signs of illness. We sent out a thyroid panel two weeks after the initial low t4 and the results were as follows:
t4 total - 0.3 ug/dL
free t4 - 0.35 ng/dL
TSH - <0.01 ng/mL
Should we treat her as truly hypothyroid? She has never been hyperthyroid and has never been treated with methimazole. Is there value in trying to use the Standard Process product Thytrophin PMG or should we just start her on thyroid hormone?
Thanks in advance,
Kaley Fuchs, CVT
What breed is your cat? Female, spayed?
I'm assuming that you did routine blood work (CBC, serum chemistry panel, urinalysis) in addition to the T4. Were there any abnormalities on this bloodwork or urine?
Is you cat showing any clinical signs of illness (decreased appetite, vomiting, diarrhea, respiratory signs)?
What lab did you use to measure the thyroid panel?
Hi, my cat is now hypot following hypert surgery to remove one enlarged gland.
My vet tested his T4 four weeks after surgery and says he is now hypot and asked to see him again in six minths.
My cat is also Diabetic and prior to surgery was managing using Tight regulation free of insulin, two wks after surgery his diabetes has been difficult to control
This week he has started to show signs of decline. A little sickness, runny stools and very very lethargic. Appetite reduced.
Should my vet be considering hormone therapy?
In general, most cats will develop a low T4 for 4-6 weeks after surgery but these cats are generally not showing any symptoms.
If your cat is showing clinical signs of lethargy, I'd retest in a couple a weeks and run another serum T4 level but also do a TSH level. You should also check the serum kidney tests, if not already done recently.
If the T4 is low and the TSH is high, then I would start L-thyroxine supplementation (0.075 mg, twice a day) for at least 2-3 months.
Hi Dr Peterson,
My 4 year old neutered male cat suddenly gained weight over the past year while the other cat is normal weight. There was no lethargy that I noticed and his coat was sleek and shiny. The vet sent blood to the lab (only T3/T4), and the test showed his T3 to be low <40 (range 40-100), but a specific number was not given, and the T4 was normal. They put him on Levothyroxine 0.1mg once daily. My vet is not good at explaining things so I'm not even sure this is the right treatment for him. Thank you.
A diagnosis of hypothyroidism can never be made on the basis of a low T3 (and this may not even be low, since <40 is the lowest the assay can measure, but we know that normal range in cats can be much lower-- to 25 or so).
To make a diagnosis of hypothyroidism in a cat, we would want to do a full panel of thyroid tests, including a total T4, T3, free T4, and TSH. If a cat is hypothyroid, T4, T3, and free T4 should be in the low to low-normal range, but the TSH value should be very high.
So could your cat be hypothyroid? Certainly possible, but quite unlikely. Only 2 cats with spontaneous hypothyroidism (that is, not associated with treatment for hyperthyroidism) have ever been reported. If all cats that we overweight were hypothyroid, this would be an epidemic!
Thank you so much for your post. This cluster of symptoms describes my little "red dwarf" perfectly and the kitten in the photo could be his littermate. After spending over a thousand dollars on enemas, laxatives, special food, and x-rays it is a relief to see that he is going to survive and will live as close to a normal life as is possible. Couldn't have done it without your website.
(His TSH was 260% over normal. Not bueno)
Thanks again
Good news -- at least you figured out the diagnosis. I'm really glad that my posts helped!
Hello Dr. Peterson,
I have a 17 moth old Dwarf male neutered Domestic Short hair Feline Named Haymitch who has just been diagnosed with Hypothyroidism.. I am wondering what dose of Levothroxine Sodium you would recommend him on. His levels are as follows
TT4 -11
TT3 -.1L
FT4 -4L
FT3 -3.3H
TSH -2.69H.
He has had colon reduced once then removed including the ileocecal valve. His growth plates are still open as well. He did have bladder stones and does have kidney stones as well. He is currently having to receive a enema daily. The lab he was tested at is recommending 0.1mg BID, and my boss/veterinarian is recommending 0.05mg BID. Being that this is the first case of feline Hypothyroidism we have experienced we were looking for some recommendations.
Thank You
I agree with your boss. I would start at 0.05 mg (50 µg) twice a day, ideally on an empty stomach. Then retest the serum T4 and TSH level in a month, with samples collected 4 hours after you give the L-T4 supplementation.
Adjust the L-T4 upward to 75 µg twice daily if the TSH stays high - we want that to normalize. But we don't want to overdose and produce hyperthyroidism!
Thank You very much for your quick response.
Dr P, I have an 11 y/o spayed female who became hypothyroid post I-131. We have her on Levanta and her T4 is in the range with low TSH. I have heard others with post I-131, hypo kitties who have told me that supplementing with T4 will drive down her T3 and she will need T3 supplementation. What is your experience with this? Is this something that I should bring to the attention of her vet?
Dr P, I have an 11 y/o spayed female who became hypothyroid post I-131. We have her on Levanta and her T4 is in the range with low TSH. I have heard others with post I-131, hypo kitties who have told me that supplementing with T4 will drive down her T3 and she will need T3 supplementation. What is your experience with this? Is this something that I should bring to the attention of her vet?
(sorry if this is a duplicate post)
T4 is normally the main hormone secreted by the cat thyroid gland. Very little T3 is normally secreted. In the cat's body, T4 is converted to T3. Some cats may do better with receiving both L-T4 and L-T3 but most do well on T4 therapy alone.
Giving T4 in no way "drives down T3" levels.
Hi Dr Peterson,
You have already treated two of my cats (Luigi and Jack) at your Hypurrcat Clinic.
I also have another cat who is approximately 6 years old and was never treated with radioactive iodine but is suspected of being Hypothyroid. His appetite has decreased, he is lethargic, has gained weight, and has had hair loss on his ears. A full blood profile was run through Idexx.
His T4 was 1.6 (reference range of 0.8-4.7 ug/dL)
Free T4 (ng/dL) was <0.3 (reference range of 0.7-2.6 ng/dL)
Free T4 (pmol/L) was <3.9 (reference range of 9.0-33.5 pmol/L)
cTSH was <0.01 (reference range of 0.05-0.42 ng/mL)
The rest of his blood work was normal. What do you make of this? My vet thought his TSH was normal but doesn't know why his FT4 was so low and doesn't know what to do next.
I would appreciate your advice.
Thanks again!
Hi Erin, most cats with low total or free T4 values do not have hypothyroidism, which is very rare. Most have low thyroid values because of another nonthyroidal illness. If your cat was hypothyroid, the TSH value should have been elevated, not low.
Talk to your vet about continuing the workup, looking for why you cat isn't eating well and is lethargic.
Hello Dr. Mark.
My name is Marta and Im from Portugal.
Recently one of my cats (a female with 4-5years) was diagnosed hypothyroidism. The vet have never had a case like this in his life and because of that he didnt know very well what to do, so, he prescribed Thyrax 0,025mg (this is sold in Portugal to treat low levels of tyroid in humans). She has been taking the pills for one month and there were no secundary effects. Today Im going to take her again to the vet to check again her thyroid levels. I do think the cause of her hypotyroidism was a food change. I was giving her and my other 2 cast Whiskas, but I changed to sterilized cat food around 1 year ago,and she started to loose fur last year. And now I'm pretty sure she started to develop hypotiroidism after this food change, cause I read somewhere that food with low levels of iode can also cause hypotyroydism.
What can you tell me about this situation?
Thank you!
Marta
Hypothyroidism is very rare and should be diagnosed on the basis of a low serum T4 value with a high TSH value. If this has not been done, have your vet do those tests.
Both very low iodine or high iodine diets can lead to hypothyroidism in people and the same may be true for cats. I recommend feeding a variety of brands and flavors to avoid such deficiencies or excesses in iodine and other nutrients. Once the diet is changed, your cat's thyroid condition could resolve.
Hello again Dr. Mark.
So, we went to the vet and he says the pills are working. The thyroid levels of my cat are now a bit higher. He says that I should continue giving her the pills for 3-4 months more.
Im also going to change to another food, to see if she gets better with it as well.
About the T4 value and TSH value, I have no idea of the values, since I know nothing about it as you can imagine, but I do hope she gets better very soon.
Thank you so much for giving me some min of your precious time.
Greetings from Portugal
Marta
Hello Dr., I have a four month old kitten who was diagnosed with congenital hypothyroidism a month ago and prescribed the recommended twice daily dose of .5 levotthyroxine. She seemed to be improving, but suffers from asymetrical dwarfism as well and her wobbliness is now gettting worse. She seems more lethargic again, very blurry eyed, can no longer climb at all, and even drags her hind-quarters some when she tries to start walking. Her back end looks way fuller than her front. Would this be most likely from constipattion? She has healthy brother who uses the same litter box, so it's hard to tell what's hers and what's his. Is there something I can use to clean her out more quickly than slippery elm? Maybe fish oil? She has a vet appt in two days, but I have a strong feeling she needs interventtion sooner than later.
Call your vet now to discuss this.
Hi, I have a 9 week old kitten that I've had since he was about 3 days old. When he was about 4 weeks old he developed an abscess in his inguinal area which we lanced and treated with clavamox. While on clavamox his appetite wasn't great and he had soft stool so we attributed his lack of growth at that point to that. Once off the abx his appetite picked up but he still wasn't growing. We ran thyroid tests when he was 6 weeks old and his T4 was 1.1, fT4 was 24, and TSH was 0.11. He's had issues with straining to defecate but has not been constipated to the point of needing an enema. He is also bilaterally cryptorchid which I've read is common with congenital hypothyroidism. I've also read that TSH is typically high with hypothyroidism and his is in the normal range. Based on his lab work and symptoms do you think he should be treated and/ or retested? I've never seen a 9 week old kitten as small as he is. If I found him on the street now I would think he was 4-5 weeks old. He is otherwise acting normally and eating well.
Based on the thyroid panel, your kitten is NOT hypothyroid. Unless you suspect lab error, I see no reason to retest him.
Hi. I am a vet tech in Tennessee. I have a 10 year old DSH neutered male. Recently diagnosed with CHF. Gradually losing weight over last 6 months. After diagnosis of CHF, sent off thyroid test. It shows Hypothyroidism. He has no other symptoms at all. Never been treated for hyper. All chemistry and cbc normal. Any ideas?
To diagnose hypothyroidism in cats, we need to find a low to low-normal total T4 concentration together with a high TSH value. Did you measure TSH? If not, that should be done. If you did, please let me know the T4 and TSH values so I can interpret them for you.
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