Hello, it's Anthony Chadwick from the webinar Vet welcoming you to another episode of Vet Chat. I'm really pleased today to have Doctor Martin Whitehead with us, researcher, veterinary surgeon, ex, also from Liverpool and alumni of Liverpool University where I studied as well. So great to have you on the podcast, Martin.

Hello. And we're gonna be talking today about hyperthyroidism, which I know is one of your many passions. But perhaps before we do start, tell us a little bit about that very varied history that you have on your slightly er circuitous path to becoming a vet, you've done some really interesting stuff before you actually trained to be a vet, didn't you?

Yeah, I, I did a, a psychology degree, and then I did a PhD studying basically how, how ears work. And at, at that time, it wasn't really, known at all how they work. They can detect sounds so small, it just seemed impossible, and it was worked out that there's actually a, a mechanical amplifier inside your inner ear that vibrates in response to the sound that comes in and builds up the.

The, the, the, the vibrations in the ear, and little sounds leak out of the ear as a result of that, they're called out to acoustic emissions. I did my PhD trying to work out how they were produced and how they relate to hearing, and that went on to be to lead to the development of clinical tests, so newborn babies are tested for that to see if they can hear these days. And as I was working away on that in the USA I I worked in Houston and Baltimore and Miami studying this stuff.

Over time, people who were interested in wild animals would call me up and say, can you use this test to see if they've got hearing problems? So I went off to San Diego and we caught elephant seals and other seals on the beach and tested them and I tested manatees and other things. And at the same time I was sort of losing interest in the, the, the science way of life, you end up.

Spending your life getting grants rather than actually doing the science, so I retrained as a vet thinking I might do wildlife stuff, but then I got really interested in the internal medicine, so that's what I do now. That's fantastic, Martin, and obviously we've all heard of the BAER test which I know at Liverpool, Jeff Garrett was a big fan of that. This is obviously, you know, a further development on the test as well, isn't it, a more recent test, your 02 acoustic emission test, which, as you say, it must be very satisfying to see a test that is now used internationally and that you were involved in developing.

Oh yeah, it's it's, it's great to look back and and see that you've done something useful. Among a team of lots of other it's really good. Yes, yeah, yeah, no, absolutely.

I know, today we, we want to talk about hyperthyroidism. I know it's a big interest of yours and obviously as a great cat lover, it's, it's been a big interest for me as well and. I remember researching it when I was doing my dermatology certificates, and I, cos I had a case of a cat that was just sort of licking and scratching and actually by treating its thyroid medically, we stopped the scratching, and this had been a cat that had been on steroids and everything and it was quite a complex case, but we got it better.

And, and really at that stage, hyperthyroidism was building up in it in its incident. Because this is a disease that if I, if my memory of the literature is right, was really only diagnosed in the 70s, wasn't it? Yeah, Mark Peterson as a definitive diagnosis he was the one who recognised it about 78, I think.

And it does I think it was 78. Yeah, not been around before that. Yeah, and now it's just incredibly common in the Western world.

And it's really interesting, obviously both of us keen environmentalists, I remember reading a report about, you know, coating of cans, but I know you also think there's other pollutants that are involved and actually you've seen some of the research on that. So perhaps tell us a little bit about why you think. Hyperthyroidism has come from kind of not very common at all to becoming such a, such a, a common endocrinological disease in cats.

Well, yeah, the, the, the truth is, we don't know why it's become so common, but there are suggestions. There's probably a genetic component because certain breeds seem to be a bit protected, Siamese, and Tonkinese, Burmese, so that does suggest maybe a genetic component, . But the, there's a lot of circumstantial evidence, correlations really, between levels of certain chemicals in the blood of cats.

hyperthyroid cats have high levels of these chemicals in their blood compared to age match control cats. And then there's risk factor evidence from epidemiological studies where hyperthyroid cats compared to control cats er are found to say eat more fish flavoured food or to eat more tinned food, and that might indicate that they're, being exposed to certain chemicals that have a structure, a chemical structure that you could imagine could be playing about with your thyroid glands. So, we don't know, but it, it's quite plausible and suggestive, the evidence that's out there, that there may be endocrine disrupting chemicals causing a hyperthyroidism in the same way as endocrine disrupting chemicals are causing things in, in humans as well and other species.

Because of course, there is so much. Chemicals, drugs that that are excreted by us if we take tablets and so on, that can go into the waterways and obviously it can go into oceans and we also know, clearly the amount of plastic that the stat I had recently was by 2050 there'll be more plastic in the ocean than fish, which is, you know, just a terrible. Thing to imagine, isn't it?

Yeah, I mean, but it's not just drugs coming out of people, it's industrial chemicals, and pesticides, and one of the key, chemical groups that it thought may be involved in. Causing increasing the risk of hyperthyroidism in cats is flame retardants put into furniture. Obviously flame retardants are a really good idea for, for the obvious reasons, but possibly they are involved in in the aetiology of hyperthyroidism too.

It's like anything, it's, it's risk analysis isn't it, you know, how many people's lives have been saved by flame retardants and sofas compared with, you know, potential. Risks of them or cats getting thyroid disease and so on. Moving on from the aetiology, obviously we've made our diagnosis, which is usually relatively routine, although there are some challenges.

Do you want to talk about anything around diagnosis that you think that sometimes we can make a mistake on diagnosing hyperthyroidism or, or perhaps not, not diagnosing it? Yeah, I mean, there, there's a whole range of issues. Most cases are, are very simple, really, but, quite a lot of older cats have, that are hyperthyroid.

And have a thyroid hormone, have a thyroid hormone in the top half of the normal range. And it's something I notice in cats that are referred to me, some of the cats who come, I look back through the history, and for several previous blood samples, they've had thyroid hormones, maybe 40 or 50, where the top of the normal range is 50 to 60. And they've eventually the thyroid hormones come above that range, but it, I would imagine those cats have been hyperthyroid, but not recognised for quite some time.

Yeah. Obviously there's the well-known problem that other diseases can suppress your thyroid hormone, so that that's one way of missing hyperthyroidism. So, you know, there, there's, and the, the other, I guess, awkwardness is, while most cats are, are pretty classic, they lose weight, they eat more, and the rest of it.

Some cats, they have this, what they call atypical hyperthyroidism. And they're more like a sort of generally ill cat, they might be off their food, but some, you know, occasionally you see cats who are hyperthyroid that way, so they're not eating a lot, they, they're quite, quite different, so I think it's more and more. Yeah, it's more and more recognised now because of course, you know, a lot of the geriatric profiles that we might do for a cat, we're looking at kidneys, we're looking at liver but we're definitely also most of the time there's a T4 in there as well, isn't there?

Yeah, absolutely, and quite a lot of the cats who come to me haven't had. Well, maybe the owner hadn't noticed anything, but they have a pre-op check for a dental or just an old age check or whatever, and, then when the vet says, well, the, the, the thyroid hormone levels up, have you seen anything? Have they been eating more on their own as they go, yeah, yeah, I thought so.

And it's sort of one of the problems with hyperthyroidism. It's such an insidious slow onset and the cats tend to be maybe a little. More active and they eat more, so they actually look to owners like really healthy cats.

Yes, and maybe lose a bit of weight and if they've been overweight anyway, that's been a good thing for them. Yeah. What's your sort of favourite treatment options there now?

How do you decide which treatment you're going to use sort of medical, surgical or or perhaps sort of a a radioactive isotope . Medical treatment. Well, you've actually got 4 treatment choices, and they all have their places, that there's medicine, but also the very low iodine diet.

And then. Management options for the disease, they don't cure it, the, the thyroid is still there, growing away, as it were, slowly over time. And then you've got two curative options which are surgery and the radioiodine therapy.

Now, obviously, I run a radioiodine unit, so I tend to be pretty keen on that, but it is, I think, generally regarded by the experts that the radioiodine therapy, under most circumstances is the gold standard treatment. Partly, obviously because it's curative, partly because it doesn't involve, a general anaesthetic for a sur as surgeries do, and partly because it has an extremely high success rate, and a pretty low side effect rate. Really, the only real side effect it can have is to make some cats hypothyroid.

There's also this business where if a cat has pre-existing renal disease. And then you cure the hyperthyroidism, you reduce the infiltration rate, and, and you can expose that pre-existing renal disease. That's not so much a side effect, it's, as such, because you're just exposing a disease that was already there.

So, but the high. The high basal metabolic rate that the hyperthyroidism was bringing was protective to the kidneys, wasn't it? Exactly, yeah, the, the glomerular filtration rate is, is high, more fluid going through the kidneys, so it gets rid of the urine and creatinine more effectively.

But there are times when radioiodine treatment maybe is not such a good idea, apart from anything else, it, it's quite an expensive one-off cost. It's over years, it's probably cheaper than, buying the drugs month on month and doing the blood tests that you often need when you're using drug treatment. But if, say you've got a 17 year old cat, you might be better off or it might be cheaper if, if a cat's not insured to treat it with drugs than it is to use radioiodine therapy.

Or if you say you had a cat with some sort of cancer and it becomes hyperthyroid, or if the cancer's going to be life limiting, maybe you don't want to be spending 2500 pounds treating with radioiodine if in 4 months' time the cancer is likely to have killed the cat. So just interestingly with the thyroid gland, what are the sort of percentages of, tumorous thyroid glands compared with. You know, a simple hyperplasia and do we know how that kind of hyperplasia develops?

the, the, the percent of cancer, thyroid carcinomas, is very low. The, the figures often bandied about something like 1 to 2%, but obviously a lot of those studies tend to come out of the places that get hyperthyroid cats referred to them. So it, I think the incidence in the general practise population is a bit lower than that.

Certainly the cats I see, and again I get a lot of the ones that don't respond well to medical treatments, and a lot of those just have, as it were, standard but severe hyperthyroidism, but the carcinomas can be included in them, and I'm probably seeing about 1% of cases that have a cancer. Mhm. How are you recognising those?

Is that palpation, they're bigger, do you do, cytology on those? What, what's the kind of, how, how do you sometimes we don't recognise them, but, if the, the risk factors for, for having a carcinoma are bigger goitres. For sure, but most cats with a big goitre don't have a carcinoma.

Having a very high thyroid hormone level, for sure, but still those with a very high thyroid, most of them don't have a carcinoma, having a very high thyroid hormone level but not having a palpable goitre because sometimes they, they sort of sink down into the thoracic in that way you can't feel them. And, having been hyperthyroid for a long time, years, even if you've been on medication, or if the cat's been on medication, because you can get a sort of, the, the standard sort of adenomas and hyperplas can undergo a sort of, . A transformation into a, a proper cancer.

And another risk factor I would say is cats who've been stably treated with medication for a long time, and then they sort of lose control and you're upping the dose of the thyroid medicine to very high levels and still not controlling it. So those are suggestive. But, really to, to sort of nail it.

I'm afraid cytology has been shown to be pretty much useless to tell, cancerous and non-cancerous apart. Histopath can do it. Histopath.

But then obviously you'd probably be removing at least, the most of the goitre you can feel anyway, cos why would you do an incision or one, you do it excisional. And other than that you can do maybe an MRI or a contrast CT. Because you're looking for mets and also scintigraphy where they, where you inject pertechate.

There's not many places in the UK that that do that, a couple of the, the vet schools do for sure. So they, there are ways to try and tell. But another, I guess you call it very, very strong indicator, but you don't see it very often, is if the goitre doesn't move in the neck.

So normally, you feel the goitre and it sort of flips and it moves under your thumb. If it doesn't do that, it's probably an invasive, thing, so that is very likely to be a carcinoma. So is that where if you're suspicious of that, you may do surgery, and is there an argument post doing that if you think there may be mets elsewhere that could be hormonally active, that you would still give radioactive iodine or would that not be effective against the mets?

Well, the, the standard treatment we do for, for your, your typical hyperthyroid cat, we give about anywhere from 70 to maybe up to 180 megabecarels of the units of ra of iodine we give. You certainly can treat carcinomas, thyroid carcinomas with radiation, but it, it's more like a dose of 1100 megabeerels. And whereas the treatment for standard hyperthyroidism has an extremely high success rate, up in the high 90%.

The treatment for thyroid carcinomas is a lot less certain. It certainly does work and it has cured some cats, but it's not something it's, if people could bring me a cat, I can almost guarantee them that I'll get it better if it's, if it's, got the standard hyperthyroidism, but I certainly wouldn't say that if it's got a, a carcinoma. A carcinoma.

No, that's really interesting and. And obviously I remember Ian Ramsey's a great friend of the webinar that I went to university with him. He, I think set up one of the first of the radioactive iodine centres.

How many are there in the country now, Martin, is this becoming a more and more common treatment? 15 that I know of. 15.

Yeah, so, several in vet schools, a few in the big referral places, so Willows in, Sonny Hull has got one, Pride referrals, Chestergate, Jeff Skerrett again, I don't know if he's still there, but he set it up. Anderson Laws has got one, and there's, there's a few places like myself where we're, . I, I suppose we're, we're not big referral places but those higher grade first opinion places.

Yeah, you, yeah, they, they're satisfying cases if you can give one injection, it saves, and it sorts the problem out, otherwise this is a problem of compliance because clients will have difficulty in killing cats, won't they? Oh, absolutely, yeah, and it's one of the big pluses of radioiodine therapy and obviously surgery too, is, is they, they don't have that problem of every day, once or twice a day, having to treat the cat and even if they're going off on holiday and yeah, so it's, it is a great thing and many cats obviously hate being hate having tablets and drops and stuff shoved down them. Yeah.

And obviously it is radioactive. What are the sort of safety precautions that you're taking and then how long is the cat with you before the client can pick the cat up up again? Yeah, the, the radioactivity is, is the bulk of the work, to be honest.

The treatment is in itself really a doddle. You have to work out the right dose of radiation to, to give the cat and make sure it's suitable for the treatment. That's for a vet, a very easy thing to do.

But to set up a unit, it is quite an undertaking in itself, going through, you have to get a permit from the Environment Agency, and that is. A, a, a, a scary amount of work, you have to have a suitable site. The, the cats, and the, the vials, the radiation come in, have to be shielded from the public and your staff, and the easiest way to do that is just with distance.

So you, you can't really set up a radioiodine unit in a room in your hospital, for instance, or if you did, you'd have to have a very large amount of lead, which is expensive and heavy to put on, on a wall. You need a very, very solid wall to do that. If there's someone upstairs, you need to shield your ceiling.

If there's someone downstairs, you need to shield your wall. So the best thing is to have a a a sort of building outside or at least on the back of your, your hospital and many practises just don't have, we were lucky we had some extra land on our site where we could put such a building. And then when you're working, it is all, it's, it's about contamination.

So we wear aprons, we double gloves, actually, we use rectal gloves, visors and, and masks and overshoes, and the levels of radiation. Are not that huge. Obviously, it's safe for the cat to be injected with it, it's not that sort of immediate damage.

What you're protecting yourself against is an increased risk of cancer from exposure to radiation over your life. You will get background radiation at a very low level. We will occasionally have X-rays or CTs.

Some people work in industries where there's a bit of radiation. If you get on a, a, a jet plane and fly abroad, you're getting an increased exposure to radiation, and you just want to, the more of that you have, the more likely you are to get cancer when you get old. So really that, that's what you're trying to avoid.

It it's you're protecting, stopping yourself getting contaminated now to reduce your risk of cancer in 30 years' time is what it's about. But it's, what sort of, how many cases are you treating a year, Martin? At the moment we do about 160 a year, and, and, and that's increasing year on year, and we, we've got the capacity to do probably 400 a year if we, if, if, if it builds up to that, which maybe it will one day.

. So you have perhaps space for two cats at any one time. I know they're in for a few days, so they may be in and out. Yeah, 1212 at any one time.

And they're all at different stages because some of them will come in the next day they'll get their injection and then they're usually for about 5 to 7 days. 3 to 10 days. So we, we have, have one or two cats gone home after 2 days if they're given a very low end dose, but yeah, it's and our maximum time in the radioiodine unit, and let's say it was a carcinoma, they'd be in a bit longer, our maximum standard time is 10 days.

No, it's fascinating. It's what was the history of, of finding this, this was presumably used in, in humans first, was it, and then translated across to cats? Yes, it's been used in humans since the 1930s, I think, might even have been 1920s.

And yeah, we, we just, vets just modified it. So I, I think again it. It was Mark Peterson, who was the first person to do it in America.

But it's been used since, I think early 80s, in cats. Cats, cats in some ways are actually a bit better designed for it than people. People have only one thyroid gland.

Cats obviously have two, sometimes a bit of ectopic tissue. So I think cats are less likely probably to become hypothyroid, after the treatment. But still plenty of them do.

And do you ever have some cases where you've had to go back and give a second injection somewhere down the line? Only one, in fact, out of well over 500 cats we treated. And, and that one almost got better, it just the T4 didn't quite get down into the reference range.

Yeah. So I mean that shows you the success rate, yeah. It's, it's fascinating, Martin, that is a pretty good success rate.

If you had that for all of your medical cases, you'd be quite happy and I think very popular with, with, with pet owners, wouldn't you? Yeah. And, and we, we do say to people when they come, if, if we don't fix your cap the first injection, the second one's free.

As I say, we've only done one second injection so far. Right. It's a, it's a good guarantee.

Martin, it's been great speaking to you. I think it's it's really good that we have these treatments for our, for our feline friends, for what has become, you know, a very common condition. Obviously we need to look at why that's happening and perhaps learn more about the aetiology and see if there are ways that we can prevent it, but I think once the disease is there.

And this seems like a, an excellent treatment compared with operating, which was always a bit of a scary surgery, wasn't it? You know, you were worried about hitting the parathyroid glands and things like that as well and causing issues, so it's . It seems very low risk compared with, with the surgery.

It, it is low risk, it's a little bit more expensive. I mean, a unilateral thyroidectomy is, is a fairly quick, easy thing really, but most cats who have a unilateral thyroidectomy become hyperthyroid within a year or two, with the other glands, so, but the bilateral one is, you know, it does have quite a high complication rate, especially with this, the low calcium because of the parathyroids, yeah. And the, the nice thing is of course the iodine is very specific to the thyroid, so it doesn't attack the parathyroid gland.

Exactly, beautifully specific, yeah. Yeah, fantastic. Martin, it's been a thrilled to have you on.

Thank you for all the great work you're doing in this and and in your other sustainability and environmental areas. All right, thank you very much.