Good evening everybody and welcome to tonight's session. My name is Bruce Stevenson, and I have the honour and privilege of chairing tonight's webinar. We have a fantastic speaker lined up tonight and a topic that we all see on a more than regular basis.
But I have to come clean. We have had, some technical issues during the day. So what we've done is we've chosen to record the session.
Just to make sure that we don't lose any contact with our speaker. She is online with us, but as I say, it is recorded. Any questions, as always, into the Q&A box, and then we will take those questions at the end.
And as long as Sarah is still with us. If not, don't stress. We will get those to Sarah and she can answer those by email.
Another little heads up for you towards the end of the webinar, my controller Kyle in the background is going to drop a link into the chat box for our webinar vet annual survey. Now those of you that have been with us for some time will know that we do these surveys every year. This is our channel, people.
When I say ours, I mean us vets. It is for us. It's driven by what we want.
And the webinar vet is absolutely fantastic in listening to what we want. So I encourage you all to take part in that annual survey and voice your opinion to the team at the webinar vet because they do listen and it is absolutely important. Just as an extra little by the buy incentive, there is also 1000 pounds in the lucky draw for one person, who completes the survey.
So watch for that in the chat box at the end. Kyle will drop it in. And then, please give us your opinion.
It really is something that is valued by the webinar vet team. So that's it from me. Let's get the recording going.
So Kyle, if you would start and then we'll get the questions at the end. Hello, and thank you so much for choosing to listen to this webinar, which is all focused on diagnosis of hyperthyroidism in cats. My name's Sarah Caney.
I'm a UK based specialist in feline medicine, and I have my own business called Vet Professionals. And you can, if you visit the website, which I I would obviously love, you can find all sorts of resources, many that are free to access, but also including some books on feline hyperthyroidism, which I've included a screenshot of on the screen. The ebook is the one on the left, which is a little more up to date than the one on the right, which is the print version.
You can see the one on the left has a thyroormish front cover. So that includes information about liquid anti-thyroid medications, whereas the print version is, sadly a little bit older, so it doesn't have that information. But it's my pleasure to talk to you about this condition, because, whilst it is something that I think, many of you will be extremely familiar with and probably find for the majority of situations quite straightforward, there are definitely from time to time, some cases that can be a little bit more challenging.
And so I hope through the next 40 minutes or so, I'll be able to share some useful tips with you in terms of how we can best optimise our ability to diagnose this condition. And one of the other resources on the website is shown on this slide, which is a free to access, very opinionated, non-referenced, but basically frequently asked questions about feline hyperthyroidism that you might find useful to download. So, what is hyperthyroidism and what do we know about it?
Well, it's a clinical syndrome, which results from excessive circulating levels of the thyroid hormones, T3 and T4. And in its most severe cases, when it's been untreated for quite a long period of time, Typically associated with severe weight loss. And you can see how thin Anna is in this picture on the left, the before treatment picture.
You can even see the bony outline of her, her legs because she's lost a lot of weight. But also you can see in this image some other clinical signs of hyperthyroidism being manifested in that, she looks quite unhappy and she was a very feisty, very tricky. Irritable, anxious, hyperactive cat, the sort of classic cat suffering from hyperthyroidism.
But happily, this is actually a very treatable condition, and indeed, we have some curative options. I'm talking about treatment in a next webinar for the webinar vet, which is slated for June of this year. And Anna had radioiodine because she was impossible to medicate.
And so she was referred for radioiodine, and her owner kept in touch with me afterwards, which was lovely, and she sent this photo. This is Anna about 3 or 4 months after her radioiodine, and you can She has much more contented expression. She's filled out considerably.
She was, you know, a little bit overweight, I'll be honest. But illustrating that it's not necessarily a bad news diagnosis to make in our patients, they can do extremely well. So what do we know about the causes of hyperthyroidism?
Well, in the overwhelming majority of cases, almost all cases, if you histologically assess the thyroid tissue, then what you will find is benign hyperplastic changes, sometimes called adenomatous hyperplasia. Mostly, or more commonly affecting both thyroid lobes. There are two thyroid lobes, one on either side of the larynx, but unilateral, certainly in a proportion of cases, also sometimes involving ectopic thyroid tissue, which can be anywhere from the base of the tongue right down to the cranial thorax down to the base of the heart that has been reported.
And overall, the incidence of ectopic cases of hyperthyroid is relatively low in the general population, maybe 4% of cases. But sadly, these cases, the sort of typical way we might find out about them are cats that have had bilateral thyroidectomies and yet remain hyperthyroid. And these cats often have multiple areas of uptake, including the standard in the neck, but also ectopic tissue as well.
A very small number of cases, a small proportion of cases of hyperthyroidism are due to functional thyroid carcinomas. And also there are some concerns that very long term medical management of the benign form of the disease may increase the risk of that thyroid tissue gradually turning into something a bit nastier with time. That's certainly something that Mark Peterson has published some information on as well.
At the moment there's still a lot that we don't know about hyperthyroidism, including fully knowing what causes this condition. Various factors have been looked at, including the amount of iodine in the diet. exposure to various pollutants in the environment, including flame retardants and air fresheners, for example, genetic influences as well.
But at this stage we don't fully understand exactly what is going on and it's currently, thought to be a number of factors that are interacting, but the end result is that the thyroid tissue is working autonomously to produce excessive amounts of thyroid hormones. And risk factors for this condition that we know of include increasing age. This is definitely an old cat condition, so many of our patients are over the age of 10 when we make this diagnosis.
There is certainly, according to oopsie, a recent study, that the RVC increased risk in long-haired, non-cubred cats. And use of cat litter and feeding a predominantly canned food diet and fish-based canned food have also been reported as risk factors recently. There are some genetics involved in this condition in that we know certain breeds of cats appear to be less vulnerable to developing hyperthyroidism than others.
So Siamese, Burmese, and the other breeds listed on this slide, do have a decreased risk of hyperthyroidism, but importantly, they do still get this disease. So if you see a thin Siamese with a goitre, you know, it's very likely to have hyperthyroidism. You're just likely to see fewer Siamese overall being diagnosed with this condition.
And, vaccinations, use of flea products are not currently thought to be risk factors for this condition, but a lot, a lot we don't know, and it's a relatively recent illness that we've been been aware of. Mark Peterson, the, the god of hyperthyroidism, in my view, was the person who first described this condition in 1979, which is a long time ago, but, also not that long ago. So most of the cases we see are older cats, mean age 10 to 13 years.
But we do see a proportion of cases diagnosed at a younger age. So overall, maybe 5% of cases are 7 years old or younger, and very, very occasionally, it has been reported in cats under the age of a year. So, don't rule it out just on the basis of age, although, of course, it is much less likely in those very young animals.
One or two studies have tended to show a slight predilection in females, but that has not been uniformly borne out. So I think mostly we would say there's no obvious sex predilection. And generally around the world, where prevalent studies have been published, it's been around about 10% of elderly cats in which This condition has been diagnosed.
And that has led to ICA care in terms of their preventative healthcare recommendations and guidelines, encouraging us to include screening for hyperthyroidism in all apparently healthy cats aged 11 years and over, where possible, just because it's out there, we know. About 10% of UK cats have this condition, and therefore, it puts us in a better position to diagnose it as early as possible, which is likely to result in a better outcome because clinical signs do get more severe as the disease becomes more long-standing. So untreated cases of hyperthyroidism, are more severely affected, according to the duration of their hyperthyroidism, as well as presence of other concurrent disease.
The thyroid hormones have a number of impacts. They act on all of the cells of the body, so they tend to increase the things on the left hand side here, so increase heart rate, increased metabolic rate, increased gastrointestinal motility, and CNS activity, and decrease sleep and body weight. And the major clinical findings as a consequence of this will include weight losses that the most common clinical signs and typically also in association with a palpable thyroid nodule, although you'll notice it's not 100% of cats that have a thyroid nodule, it's it's 85%.
Cardiovascular abnormalities are common, so heart murmur, tachycardia, and gallop rhythm, for example, very, very common. The association between hyperthyroidism and hypertension is still actually a little bit unclear, a little bit controversial in terms of where that hyper thyroidism causes hypertension, or whether there just is a strong association between both of these conditions and the age of cats. And we know about 20% of elderly cats have high blood pressure, so it's not that different a proportion compared to those with hyperthyroidism.
And certainly, also sticking with that theme of hypertension, we know that cats with hyperthyroidism that do have hypertension diagnosed need treatment for that hypertension, typically for the rest of their life, even if you cure the hyperthyroidism. So the nature of the relationship between these two is still under a little bit of debate, but important for you to know that you can't just treat the hyperthyroidism and, and the hypertension will disappear. You do need to treat both of these things, independently.
As you can also see on here, an increase in thirst and urination is, is quite common although typically mild, skin and coat changes, gastrointestinal signs like vomiting and diarrhoea. Is it essential that we can palpate a goitre to diagnose hyperthyroidism? Well, clearly, as I showed in the last table, not 100% of cats with hyperthyroidism diagnosed actually have a goitre.
A number of reasons for this, including those listed on the bottom of this slide, such as Cats with ectopic hyperfunctional tissue. So if they have ectopic thyroids, then clearly they, they may well not be palpable if they're in, for example, the cranial thorax, but also hyperthyroid cats are not always the easiest to examine. They can be a bit tense and irritable.
The goitres can be quite small as well. And indeed, conversely, if you have a large thyroid, it can sometimes slide down the neck with a little bit of gravity into the anterior thorax. If you're needing to do a thyroidectomy or wanting to do a thyroidectomy as your management, then clearly you do need to have a goitre that's accessible.
But beyond that, you don't need to have a goitre to make this diagnosis. The diagnosis is really made on the blood tests. But certainly in terms of raising the suspicions of hyperthyroidism and corroborating the other findings, including blood test findings, then it is useful to be able to palpate for a goitre and document a goitre.
So it should be a routine part of your examination, particularly in your older cats. Some tips and tricks for for those more tricky cases, smaller goitres, try varying the cat's neck position. So if you turn the cat's neck to one side.
Then the skin on one side becomes a little bit tighter, and it often gets a bit easier to feel that little mass. So if the cat's head is turned to the left, then feeling a small right-sided nodule can be easier. Try standing behind the cat versus in front of the cat.
Try palpating with one finger rather than two. All these things sometimes, you know, you'll find this a nodule just appears. Sometimes it can be also useful to clip the fur, and it's certainly if you're doing a blood sample, you might need to clip the neck anyway.
So maybe just extending where you clip a little bit if that's OK with the owner, wetting down with surgical alcohol as well. This patient, the photo on the right is from a patient, obviously, it's going for surgery, and you can visibly see the thyroid is very much easier now that it's all clipped up though compared to to the conscious cat. And if you have access to sintigraphy, this is lovely actually, for hyperthyroidism.
So this is perhaps those clinics that have access to a scanner, they maybe do bone scanning. You give an injection of radioactive technetium, which like iodine, is taken up by the thyroid and concentrated there, but has a much shorter. Half life than radioactive iodine, but it actually shows you where the thyroid tissue is.
And so what we have here is a scan from a cat where its head is towards the top of the picture, and the bright areas within the head are actually salivary tissue, which also takes up technetium and iodine. Then if you move down the picture, you've got the cat's neck. There's nothing going on in the neck.
Come down a bit more, you can see a little bit of each leg, at each side. But then we've got the cranial thorax, where there is what looks like quite a large, very, very, very hot area. So it's hotter than the salivry.
Tissue, that means it's hyperfunctional. We should see the thyroid with the technician, but in a healthy cat, it would be the same level of uptake as the salivary tissue. And then below that very hot area, there is the heart, which is visible just because it's got some radioactive blood within it.
We're getting better, I think, at finding hyperthyroidism in those sort of classic cases, but there are some cats that present with more unusual clinical signs. For example, there is a hyperthyroid myopathy that we do see from time to time. It can cause this very severe muscle weakness and the ginger cat in that top picture.
Have this, so some ventroflexion of the neck, profoundly weak, as a result of that hyperthyroid myopathy. Also, we can sometimes see in association with myasthenia gravis, and and that's illustrated in that bottom picture. Cat with such severe weakness, she's just resting her head.
She had a a combination of hyperthyroidism and severe generalised, myasthenia gravis. Tic near can also be a very dramatic feature in some cases, this sort of open mouth breathing. Not all of these are due to severe heart failure.
Which would be one cause of that severe tachyne, the, the hyperthyroid, heart failure, if you like, because of that cardiac remodelling and untreated hyperthyroidism causing congestive heart failure. In some cases, it just is, I think that the high levels of thyroid hormones, everything is just jangling, and the cat is severely dysic as a consequence of that. Cardiovascular abnormalities are common, but generally actually don't have a clinical consequence to the patient.
So the tachycardia, the, even the carddiomegaly, the, the left ventricular hypertrophy on echo or visible on an ECG isn't something. That has, you know, clinical consequences that we need to address, but if untreated, will progress to congestive heart failure, which then does need to be managed. And the cardiac changes are reversible with treatment, but it can take a long time for them to reverse as well.
So our diagnosis relies on us, firstly, looking for clues of hyperthyroidism, but also ruling out other differential diagnoses, doing our general tests for hyperthyroidism, which is really the resting or the basal or the total T4, depending on which terminology you want to do. And then, if needed, potentially, additional tests, but usually it's just the top three of these that we need to do. To, confirm the the cause of the, the cat's problem and also whether there are any concurrent issues.
Key differential diagnosis for hyperthyroidism, well, weight loss with a good, normal or increased appetite, these would be some of the important differentials to consider, so inflammatory bowel disease, diffuse alimentary lymphoma, diabetes, ex-crime pancreatic insufficiency, some cats with lymphocytic cholangitis, a form of liver disease also. Will be quite polyphagic. So those are all important differential diagnoses, some of which you will see clues on other laboratory tests like diabetes, probably being the most straightforward example of that.
Increased thirst, chronic kidney disease, diabetes are the big differential. So again, your urine dipstick comes in very, very helpful here. Hyperthyroidism does typically cause a mild reduction in urine specific gravity, so it can be hard to easily assess presence and severity of kidney disease in cats with hyperthyroidism.
And then the heart murmur, well, the most important thing is to make sure you do assess blood pressure because high blood pressure can also cause heart murmur due to the cardiac remodelling, but of course, there is the possibility of primary cardiac disease or even anaemia, ahemic murmur, which again, you're going to pick up when you do your, your blood tests. So your routine lab tests, where possible, would include haematology, biochemistry, urinalysis. Most common changes you're going to see are going to be a mild to moderate increase in liver enzymes, ALT, alkaline phosphatase, often an erythrocytosis, sometimes a leukocytosis and microcytosis, on your haematology.
The total T4, also known as the basal or resting T4, generally a good test to do, generally quite sensitive and specific for the diagnosis of hyperthyroidism. So often a single test result is all you need. But I guess the key thing to, to remind you about here is that, you know, tests are not always perfect.
Even good tests sometimes go wrong. And if you get a test that doesn't agree. With your clinical hunch, then don't doubt yourself.
Do the test first. Medics, as you probably know, and those of you that like your medicine will probably already do this. If we get a result that surprises us and we can't quite explain, the first thing we do is repeat it to see whether it's actually some sort of lab artefact rather than us, you know, getting all worried about a new complication we've not thought about.
If we do our total T4, and it comes back as normal, and there is a high clinical suspicion of hyperthyroidism, then the most likely possibility is that the cat has got severe concurrent illness that is suppressing total T4 levels, what we call the sick e thyroid phenomenon. In cats that are less severely affected, so not looking like this ginger cat here, another explanation can be, if you have early or mild disease, that that T4 levels can fluctuate a little. So they can occasionally reenter the reference range.
And that's why if you have a result in The high, the upper half of the reference range and you're considering hyperthyroidism as a possibility, it doesn't completely rule it out, and you'll see that comment often from your laboratories as well. But usually if the T4 is in the lower half of the reference range, hyperthyroidism is unlikely. So this is a schematic example of what might happen in in patients with early disease over a period of a couple of weeks with the T4 results on the Y axis and the days on the bottom axis.
If you take a number of samples, you might just be unlucky with some of them being a bit borderline versus some of them being within the reference range, but typically, the lowest they might be is the midpoint of the reference range. If you repeat that total T4 and you still are having a normal result, or indeed, if you just feel like you just wanna go, let's do what we can to, to nail this diagnosis, then this is the time you might want to consider doing a free T4. And this is a very unappealing looking slide, but I'm going to talk through it.
I just find this paper by Mark Peterson very helpful in describing the, the utility of the different tests we have available to us. And this slide shows the results from a study where over 1000 cats that Mark Peterson saw, where hyperthyroidism was very much a differential diagnosis, these cats, you know, had compatible clinical signs, such as weight loss. And ultimately, the diagnosis of hyperthyroidism was confirmed, I think by sintigraphy, but it was definitively confirmed in 917 of these cats, versus other non-thyroidal disease being confirmed as the cause of the problem in 221 of the cats, the results of which are in the right hand column.
So the hyperthyroid cat results are in the left hand column, the non-thyroid disease cats results are in the right hand column. And then what he did in this study is, he just literally looked at the total T3, total T4 and free T4 results and allocated them to the categories of either high, normal, or low. The T3, we, we don't really talk about it, and you, but you can see why that is, because it was only high, so it only had a sensitivity of 67%.
So it's high in about 2/3 of hyperthyroid cats, but about a third of hyperthyroid cats is normal. So T T3, don't bother with that. But the T4, meanwhile, the total T4 was high in 91% of cats, and normal in 9%.
So it has a sensitivity of 91%. It doesn't quite identify all of them, but certainly a good number of them. But importantly, it doesn't have any false positives.
So none of the cats with non-thyroidal disease had a high total T4 in this study. The free T4 is helpful and it is more sensitive in general. So the free T4 was high in 98.5% of these hyperthyroid cats.
So it has a much higher sensitivity, but unfortunately, there were some false positives. And this is why the total T4 test has been recommended as your screening test, because whilst the free T4 is more sensitive, there is a risk of false positives in cats with non-thyroidal disease. More recently, Mark Peterson has added to this work by incorporating some TSH data from a similar sort of group of cats, but also adding some healthy age match to control cats.
So we now have the cats that were confirmed to have hyperthyroidism. We have a small number of cats in which hyperthyroidism was considered, but ultimately something else was diagnosed, and then we have a quite a reasonable number of Healthy age matched cats. And what you can see is that the TSH is typically low in cats with hyperthyroidism.
98% of cats with hyperthyroidism have low or undetectable levels, but unfortunately, it is also low in 15.6% of cats with non-thyroidal disease and about a third of your healthy older cats. So we can't use the TSA.
As a screening test. But if we add it to other tests, it becomes helpful. So, for example, if you look at the hyperthyroid cats that had high 3 T4, none of them had measurable TSH, whereas the suspect cats, cats that often had other illnesses, those that had high 3 T4 typically all had measurable levels of TSH.
So the, the, the summary point here really is that the TSH assay is sensitive, but it's not very specific. So 30%ish false positives, which is obviously very problematic as a screening test. But if you add it to the total and or the free T4, you get a high sensitivity and a specificity.
And also, I think worth saying that if you're a bit sitting on the fence, is this cat or is it not hyperthyroid, and it's T4 or free T4 results are maybe a bit equivocal as well, if the TSH levels are measurable, then it's very unlikely. This is a hyperthyroid because only 2% of hyperthyroid cats in this large survey had measurable levels of TSH. So obviously there are some that do, but if you're sitting on the fence, maybe monitor that patient rather than going for treatment at that point.
So in summary, the diagnosis of difficult cases, consider repeating the T4 if you get a normal result and also consider maybe using a reference laboratory if you're using in-house equipment, just in case there's any issue with the reliability of the assay that you're using. You can do a free T4, preferably by equilibrium dialysis. If you find that your free T4 is high and the total T4 is in the upper half of the reference range, it's very likely that your patient is hyperthyroid, of course, especially if they are symptomatic, and the endogenous TSH can also be helpful, typically low or undetectable levels in your hyperthyroid cats.
If you do all of that and you're still not sure, then this is the point where I definitely start by looking more closely at other areas of the cath, particularly the gut, the bowel is often the next logical place to consider as the cause of the problems. There are other thyroid tests that you can do, and, they are, again, not perfect. So the T3 suppression, TRH and TSH stem tests, none of these things are, are perfect.
Like all of the dynamic endocrine tests that exist for small animals, but they can add some useful information. But I rarely do them now. I, I'm more likely do what I've described in terms of the free T4 and a TSH and then, you know, rethink.
But also always remind myself that hyperthyroidism is not an emergency. So if I really don't think I can nail that diagnosis now, you know, I'm, I'm better to just monitor that patient, and look for other explanations. If you do have access to sintigraphy, I do think that is extremely helpful in these sorts of cases though.
And this just shows an example of sintigraphy in a cat. So it's, this is a cat that now you can see has got a hyperfunctional thyroid tissue actually within the neck. So it's in the right part of the body.
We know it's hyperfunctional because it is more dense on the scan than the salivary tissue. So in a healthy cat, you should have the same amount of uptake in the thyroid to the salivary gland. But in this cat, you can see this very, very hot thyroid there.
Subclinical hyperthyroidism is a term that you might hear people refer to, not an awful lot known about this in cats, but certainly in people that there is a subclinical period of hyperthyroidism before overt hyperthyroidism develops. And the reason for mentioning it is, is that from what we know in cats, it does exist. It probably is a 1 to 3 year period before the overt hyperthyroidism comes, comes out as, as it were.
But during that period, these cats often will have a goitre. And so if you are doing a good preventative healthcare, you're seeing your old cats frequently and you palpate a goitre, but the cat has a normal total T4, this cat is still, I think, one worth keeping a closer eye on. You could at that point do a TSH and often you, you will find that slow.
But even if you do, you may not on those grounds alone, if the That is, is clinically free of any sort of signs of ill health, you're probably just going to be monitoring rather than treating. And certainly, my understanding of subclinical hyperthyroidism in people is that it too is a sort of monitoring period rather than direct treating, starting, you start the treatment once the clinical signs appear, but educate the owners, of course, as to what to look out for. Now that we're doing more preventative healthcare checks in our older cats, it's also a bit more common to see T4 results that don't quite fit in the other direction.
So in other words, we're, we're doing a routine health check of an older cat, and perhaps we think, yeah, everything seems to be fine. There's no weight loss, and we do our blood panel and international cat care recommend in cats age 11 years and over, to include a T4, so we include a T4, and lo and behold, it comes back high. Well, what do we do here?
Well, I think that the first thing again, is just to remember that sometimes laboratories, whether they're reference laboratories or our in-house equipment, sometimes they go wrong. So we can get lab era. But also, I, I would say I see from time to time, particularly in larger cats, results that are just a little bit high, or even just it really just about within the reference range, but right at the top of it.
And there is a hypothesis, that obesity can cause thyroid resistance in the way it causes insulin resistance as well, and that that might lead to a slight increase in, in T4 levels. If there's no goitre and no clinical signs, then again, monitor rather than treat, but it's all about owner discussion and owner awareness. Are we under diagnosing hyperthyroidism?
Well, probably almost certainly. There's not an awful lot of published data really to support this, but an example of, of something that I can share with you is this small study where a colleague of mine who's a veterinary ophthalmologist. Just wanted to look for ocular manifestations of diabetes melisis in cats.
As we know, dogs quite often get cataracts, cats less frequently, but she wants to look a bit more closely. So we identified 21 diabetic cats coming into the clinic. And then I also found some age matched control cats, and the control cats were all a similar age.
So these are all, by and large, senior and super senior aged cats. 110 year old, I think the others all 11 and over. And they were thought to be completely healthy from their clinic notes and from the owners, not on long-term medication, no other diagnoses that that anyone was aware of.
And all of these cats, then the diabetics and the age match control cats had quite detailed assessments, not just their eyes, but also blood pressure, blood, and urinalysis. And what we found was that actually, a third of the control cats had reduced USG. So, you're in specific gravity less than 1035.
A third had what I would say borderline, so 10:35 to 1040, and a third had a normal USG. We had a systemic hypertension, with target organ damage diagnosed in in three of our control cats, which I think is about 14% of them, so similar to the age reported overall prevalence of this condition in cats. And we did find that two of the cats were hyperthyroid, so that I think was about 10% of our, control cats.
So just about what you would predict from the UK prevalence of hyperthyroidism as well. And, 7 of the cats, but a third of the cats actually had renal disease. One did have quite severe renal disease, creatinine just under 300.
The others all had milder renal disease. And nonetheless, all of these cats, the owners thought were completely fine. So, this is the value of health screening in apparently healthy cats.
We also found that the diabetic cats that had all the same tests done, actually 3 of these were hyperthyroid, and I think all of these cats, when their diabetes was diagnosed, had had a T4 assay done. So this was, you know, a new thing, a new change, and for the cats with a T4 of 67 or 78, probably that's not going to. Be massively impacting on the cat's clinical signs, but a T4 of 214 very much expected to have a significant impact on that cat and probably going to be causing weight loss and other clinical signs.
So just a reminder really that it is common to have more than one clinical condition and things can change with time. So how can we aid early diagnosis? Well, owner education definitely helps.
What signs to look at for awareness of how common hypothyroidism is in cats, and also following age appropriate health screening in our cats, so that we are really looking at our patients closely for indications of illness so that we can pick up on it at the earliest possible opportunity. And the ICA care guidelines are under the Cat Care for Life division, and that has a separate website, catcare number 4life.org, which if you visit has information for owners and veterinary professionals, things you can download some checklists, for example.
And what they recommend is that up to the age of 7 years, our patients have an annual health check, including a body weight assessment. Physical exam, discussion of diet, all the usual routine clinical assessments are done. But then once the cat reaches the age of 7, that mature age category, that if possible, we include a blood pressure, a urinalysis, and a blood profile to that general assessment to aid early diagnosis of a range of conditions, which include hyperthyroidism, but also, of course, things like kidney disease.
And then in our senior cats, we increase the frequency of our checks to, if possible, every 6 months. And you can see we're also now doing a T4 test as well. So that's recommended as a routine in cats from the age of 11 upwards by ICAT care.
And super senior guidelines for my cat care are the same as the 11 year olds. So if possible, every 6 months that you see them, and then 6 to 12 monthly blood work and urinalysis, depending, I think, on also how stable or otherwise the patient is. But I would say there is It's definitely an argument for a health assessment that critically includes things like body weight, as well as a history and exam are justifiable every 3 months in the very old counts to pick up clinical problems at the earliest possible opportunity.
So let's look at a case example. This is Bobby, who I recently saw, he came in for a boost vaccination with, with his sibling, and COVID appointment still, Scotland's been quite restrictive in terms of COVID regs. So, by and large clients have not been coming into the building.
We've been doing lots of doorstep handing over a bit of a relay. So the client's handicapped in its carrier to one of the nurses or reception team. And then, that the cat is, passed on to us.
We do an assessment, we phone the owner, we have a discussion. And, Bobby's owners knew that that was the scores. But so they'd written some notes because they were obviously really worried about Bobby.
And the main concern, as you can see, was that, Bobby was constantly hungry and getting thinner. So weight loss in spite of him wanting to eat a lot. So when I spoke to Bobby's owner on the phone, the story was that they'd first noticed signs really about 4 to 6 weeks ago, that they really were aware he'd lost weight.
And in fact, if you look at that snapshot of his weight records, the top one was April 2022. The, the next most recent one was June 2021. So 10 months previously.
And you can see in that period of time, he'd lost a huge amount of weight. He'd lost 1.2 kg.
And I'm sure that the weight loss had been going on for longer than 4 to 6 weeks, but it had just reached a critical tipping point for the owner to notice it. Really dramatic weight loss, 21% body weight loss in that period. He'd also been a little thirstier.
He'd had increased vocalisation, and indeed his physical exam, you know, he, he'd read the hyperthyroidism textbook, as it were, so he had a goitre that we could feel. His heart rate was fast, he had a gallop rhythm, he had a heart mur. You know, he was thin.
So as I say, lots of the, the sort of typical findings of hyperthyroidism, and this is Bobby posing for a photo and his weight chart on the rights, which you can always, you know, make weight charts look look sort of better and worse, really. But as you can see, he's been Looking quite stable for several years and then suddenly nose diving on the right hand side. So we did some lab work in Bobby as well.
His haematology actually relatively unexciting in terms of abnormalities. So not really much of a significant concern there. The biochemistry, much more helpful, particularly that total T4, which is elevated, 121.
And you can see some comparative results actually from a couple of years ago. So it's T4, in 2020 was 47. So it was within the reference range, although the upper half, as you will note, no doubt.
But other than that, what we can see is his liver enzymes are actually normal, but they are both right at the top of the reference range for the machine. His creatinine is quite low, which is because he has poor muscle mass, and, that, therefore, he, he's not got much muscle turnover and therefore his creatinine levels have, have dropped, but his kidney function on the basis of STMA and subsequent urine specific gravity looking OK, although I think it's still hyperthyroidism can mask renal disease, so we need to also be aware of that in terms of passing of time. We'll talk more about that in the treatment session as well.
But by and large, no unexpected surprises, and he's read the textbook, and he has since started medical management of his hyperthyroidism, but his owners are keen for curative management, so he's actually going to be having radioiodine. He's on the waiting list currently for that treatment. If we look at another case, a bit bit more of a trickier example, this is Molly, 10 year old female neuter domestic short hair at the time.
Again, clinical signs, very much compatible with the possibility of hyperthyroidism. We've got weight loss, increased thirst. She's actually less.
Rather than more active, some GI signs in terms of soft faeces and tack it near. And in fact, tack it near was really the dominant sign for her quite marked. I don't know how appreciable it is, black cat on a black table, it makes it a little bit difficult, but she was really sort of huffing and puffing away.
And she did have a systolic heart murmur. She had lost weight, but I couldn't feel a goitre. So, so that was the thing, you know, it's a bit frustrating.
Has she or hasn't she got hyperthyroidism? There are other possibilities that could explain these clinical signs. So perhaps diabetes, inflammatory bowel disease, bowel neoplasia, kidney disease, cardio respiratory disease are all on the list.
But hypothyroidism is certainly on that list still as well. So she had some blood work and all of that was normal apart from one elevated liver enzyme, ALT 175. In-house, total T4, for her was actually a predecessor machine of the, the catalyst, which was what Bobby had.
So the snapshot, and the result of her was actually a bit like Bobby's result as of two years ago, so high reference range, but ultimately normal. And, she was referred to me for further assessment just because a colleague in the same practise. And, and, the big question, of course, was, you know, is she or is she not hyperthyroid?
And that was really the thing. Her quality of life, you know, was fine. And although she's very titnick, she was, you know, not worrying us in terms of her respiratory parameters, or, you know, colour or anything like that in terms of a critical care sense, but definitely want to understand whether or not she had hyperthyroidism.
So from my perspective, this is where I think a reference laboratory and one that really does a lot of hormone assays can be helpful. So nationwide specialist labs would be at my general choice at this sort of point, and I sent off some blood. And actually, as you can see, I, I asked for everything, but as it turns out, you know, I didn't need to because her total T4 was very high.
So the free T4 and the TSH were were sort of Essentially not really needed for Molly, but good to know. So she totally fits with the diagnosis of hyperthyroidism. I think sadly, that the in-house equipment probably let us down.
Something didn't quite go to plan. And the, certainly there's good data to support the current IDEX methodology, the, the catalyst. I'm not sure of how much was published on the snapshot, but, you know, that certainly the catalyst has good agreement.
Often with the reference laboratory results. But, you know, nothing is perfect. Things sometimes do go wrong from time to time.
And then finally, we have Isidora or Izzy, 11 year old female neutered domestic short hair with a very knowledgeable owner who has had experience of hyperthyroidism, so really knew what hypothyroidism was. And she spotted that Izzy had lost a little bit of weight, just a little bit polyphagic, a little bit of behavioural changes, a little bit of an increased thirst. Her weight loss was, you know, quite It's actually not reached that 5% threshold.
I, I, I often use with percentage weight changes. So she'd lost 4% of her body mass. So, you know, still, her owner was concerned, and on examination, she did have actually a left thyroid nodule, but otherwise, no further clinical signs to report.
Her blood pressure all fine. The referring vet did some blood work and, a bit actually like Molly in that everything was fine other than her ALT which was elevated, 148. The T4 was within the reference range.
So is she or is she not a hyperthyroid? We're definitely sitting on the fence. I saw her a few weeks later and basically repeated that and different laboratories, so different reference intervals, but basically the same results.
So the ALT for our lab was a little bit high. The T4 was up a reference range, everything else, all OK. So is she or is she not hyperthyroid is, is really the question.
So again, with her further tests requested, and nationwide specialist laboratories, total T4 there, actually pretty much the same. It's in that upper reference range. It is not above the reference range.
However, for her, the free T4 and the TSH very helpful because as you can see, the free T4 was elevated, the TSH was low. So a little bit more complicated one to diagnose, but nonetheless, we're able to make that diagnosis. And looking back at that, Mark Peterson, more recent paper on diagnosis of hyperthyroidism, Izzy really falls into this category where she's got, a normal T4 but high free T4 and no measurable TSH.
So she's, she's one of those hyperthyroid cases. So in summary, hyperthyroidism often isn't too challenging to diagnose, but on occasions it can be, and I think we need to bear in mind, firstly, that nothing is perfect. So just because something prints out a very glossy looking print out, it doesn't mean that it's completely trustworthy.
No test has a 100%. Sensitivity and specificity. So we can get false positives and false negatives.
So we need to trust our instincts, look at the cat. If something doesn't fit, then question. So in particular, question your lab results if they don't fit.
And if you're still not sure, then actually, in the case of hyperthyroidism, it will get worse with time. So if you're not sure, you can just watch and wait, monitor that cat's weight once a month. If you can see it's losing weight, test it again.
So just a reminder of some of the useful resources that I've mentioned on the website, vetprofessionals.com, but also there are some free to access guidelines on management of hyperthyroidism, which have been published in the Journal of Feline Medicine and Surgery, and which you can also download and look at and hopefully find useful. So thank you so much for listening.
I do hope that you've found this a helpful session. Thank you very much. Sarah, thank you so much.
I really, really appreciate that. As always, fascinating insights. And I do love that, that extra TSH that's been added to the mix now because you always get those complicated ones where you're sitting on the fence and, you know, you, you don't always trust yourself maybe as much as you do the lab results, .
As you just pointed out, but it is nice to be able to add that into the mix as well. So thank you for sharing that with us. My pleasure.
And probably something else I, I should have mentioned at the time, but we'll mention now is that if you are doing perhaps a repeat. Total T4. And it's, you know, being perhaps a bit equivocal in the past.
Hang on to a bit of the serum, because, TSH is stable for a few days. So without potentially resampling the cat, you can always add that on, as an option. So, avoiding that, any unnecessary needle sticks is also something I'm a big fan of for, for our sake, as well as the, the cat's sake.
Yeah, absolutely, especially when you've got a one of our beautiful feline friends who is maybe not as cooperative as what they would like, or as we would like them to be. Absolutely. Although good old gabapentin does work really nicely and lots of hyperthyroid caps and is, yeah, safe and good, good for that purpose as well.
Excellent, excellent. Before I start asking you some questions, Sarah, I just want to remind the folks, Kyle has just popped the survey into the box, the link. Please, folks, as I said to you in the beginning, this is our channel.
Let's give feedback to the fantastic. Team at the webinar vet. It really is something that they take very seriously and completing that link is so worthwhile for all of us.
And then one lucky one of us will get that 1000 pounds in the lucky draw. So please go ahead and and complete that survey for us. Sarah, I wanted to ask you, Izzy, I, I, I'm not sure that I would have started Izzy's treatment because it's such a good owner at that point if the blood pressure was normal.
Is that right or wrong thinking? So, at that point, she, she didn't have treatment because of hypertension, although actually she did subsequently develop hypertension. So whether you're subliminally aware of that, but she did receive treatment for her hyperthyroidism, even though her T4 was within the reference range.
And, I mean, I guess like you, we actually did have a lot of discussions about it because her owner. Was very, very keen for radioiodine. And I was a little bit anxious about that because I just felt, with her being so subtle a diagnosis, I was very worried about inducing hypothyroidism, which is, definitely something I'll be talking about in the next webinar.
So we, we didn't leap to it, I'll be honest, but she was losing weight, so she did start medical management just at a low dose. And we monitored her T4 and it, it fell to the lower half of the reference range. So we, we were managing it, I think, appropriately.
And then I, I did actually involve multiple colleagues around the UK, just to sort of get a, well, I was gonna say a sanity check, but, you get the feeling, you know, where I was saying to them all, really, iodine, you know, what do people think? And essentially, there was a fair amount of umming and ahhing around the country, but, we, we did decide ultimately that yes, we thought, you know, go, go at the low end of the dose protocol. And, she did have radioiodine at the Dick vet school, subsequently.
And, yeah, she, she had a, a, a slightly challenging, follow up, but ultimately was cured because of the. Do iodine. So we, we did get there in the end, but she's, yeah, she, she did cause a few headaches because of all of those things.
And I think her diagnosis was very much hastened by her owner. And, it wouldn't have been wrong, to, you know, do a little bit of that watching and waiting and monitoring. You know, if you have hesitation, because the medication.
They are, they're quite nasty drugs, really. I think that's totally appropriate. So we, you know, we, we were not straight in there.
We, we definitely had a little bit of toing and froing and discussion with her as well. Excellent, excellent. And, and in a case like that where maybe if, if mom and dad weren't so, so hot on it and that sort of thing, how would you feel about trying something like the diet approach rather than the medication approach at that stage?
Yeah, so I have used, the, hills widely, the iodine restricted food, and, your questioning, I'm, I'm really, I'm so impressed with that, Bruce, because you must do so many different topics of webinars and your questions are, are just superb, to, to, to come up with. But you're, you're sort of on, on, on the. Button as it were, and thinking, well, with a milder case, perhaps that is more of an indication for food, because typically it it doesn't seem to be, I'm going to use a, a totally inappropriate word, but it doesn't seem as potent to treatment in terms of lowering the T4.
So yes, you would have rationale for doing that. And I think as a short term measure, that would have been completely appropriate for Izzy as well, pre, pre, radioiodine, and I'm sure we actually did have that discussion, with the owner at the time, but, their preference was for, I think it's multi-cat households, so that was one of the reasons behind that decision. But yes, no, I think that would have been appropriate because I think it's a short term treatment, then, yeah.
Definitely why he can play a really important role. Long term, it often is more challenging, although I have had the occasional case where the owner, it's been their preference and it has worked well. So, you know, it, it can do.
But, but, but often it is a bit more challenging for the longer term and also a bit more challenging for the more severe cases, as you you were alluding to. Yeah, I think that's that's the thing that I was chatting about You know, I, I think Izzy, had the owners not been so on the ball, Izzy would have deteriorated clinically or become more pronounced clinically in time. And then the diet may not have been enough.
But I've certainly had cases where you've got the commitment from the owner and they're keen to go on the food. And then, as always, with cats, it's actually up to the cat, isn't it? Yes, that's true.
And I do, I do think that the fact that there is only a single food that's iodine restricted is, is makes it even more challenging because it's very challenging, often with, you know, thinking of our kidney cats, where again, we want them to eat a certain food, but at least we've got Actually a huge number now, different brands, different formulations, different flavours, whereas with poor old YD, you know, it's, there's actually, there's not much. It's just wet wet or dry and you're stuck with it. Yeah, yeah.
No, absolutely. Well, it's it's always a fascinating topic and it's lovely to see that, shall we say an old topic has got so much current interest and insights and developments and that. And I, I love those extra in inputs of the lab work and that sort of thing because the these hyperthyroid cats certainly can be a challenge.
And we don't unfortunately all live and work close enough to you. So, yeah. I'm glad for the information.
Oh, my pleasure. Thank you very much for, for sharing so beautifully tonight as well. Thank you and I look forward to seeing you on the next one.
To everybody who attended tonight, thank you very much for your time. For those of you that are watching the recording of the recording. Again, don't forget the webinar vet survey, really important.
And last but not least, a big thank you to Kyle, my controller in the background for getting the webinar, recording out. And I'm glad we didn't have technical issues, but at least we managed to bring all the info to you. So to everybody, from myself, Bruce Stevenson, it's good night.