INTERVIEW: Pilar Xifra- Part 2
(Traduction & Transcription from the Spanish Podcast available
on lagateramedicinafelina.blogspot.com/ES)
Welcome again! In this second
part of the interview, Pilar Xifra speaks about her dietary recommendations before
treating with radioiodine. She also describes potential therapeutic
complications of treatment with I131 and talks about the studies she has in
mind.
- Do you give any specific dietary recommendations before I131? May the diet influence the result of the treatment?
- Yes,
well, hyperthyroidism is caused by a tumour. That is something I always emphasize.
When we treat it, we try to favour the uptake of radioiodine by the tumour cells.
Iodine is absorbed only in the thyroid gland, which uses it to produce thyroid
hormone. If it gets saturated with the dietary iodine, the I131 uptake may not
be as much as we wish. Ideally the amount of radioiodine that the thyroid gland
takes is between 20 and 30% of the total radioiodine that we inject. However
there are cats that only take up 6 or 7%. In those cases we have to increase
the dose to compensate for the radioiodine that is lost in the urine. Whilst I
was at the hospital Puerta de Hierro, I watched how this topic is managed in
humans and I now I do the same with cats. A few weeks before treating a person
with radioiodine that person is given a leaflet with instructions about the
diet for them to avoid food with a high iodine content, like fish or seafood.
The problem are the commercial feline diets…
Precisely when you contacted me
today I was reading a paper written in US, where iodine content was measured in
different diets. A 4 kg cat needs is 87.5 micrograms of iodine. They designed a
blind study and the range (of dietary content ) was between 200 and had a
hundred and fifty-four thousand micrograms! A huge variation! And in a large percentage
of the dietary recommendations, the daily iodine intake ended up being greater
than 100 micrograms… So I talked about this with Dr Peterson. I wanted to find
out more information about this!
I thought of designing a retrospective
study that would involve assessing the dietary iodine intake before the therapy...
However that was very complicated because there are only a few cats that only
eat one type of food. The iodine content of the different diets is also very
different and is really difficult to find out the iodine content of every diet.
It is a very well-kept secret! Cecilia Villaverde suggested a prospective study,
perhaps one where a group of cats are fed a controlled diet and a second group
are fed diets has not been controlled. However I find this is also very
complicated because I do not like the idea of changing the diet to geriatric
cats or sick cats. I really do not want a sick hyperthyroid cat with anorexia!
I started recommending owners to
avoid iodine rich food such as ham or fish or sausages… But the variety of
diets, ingredients and flavours drives me crazy. However I found out that the
iodine content between tins of tuna and chicken flavoured commercial diets is
exactly the same as it gets injected into it. I recommend avoiding human treats and encourage
them to feed their cats commercial diets. Whether they are meat or fish flavoured
does not really matter. Gourmet Gold is very popular. I tried to encourage them
to feed their cats wet food, since I think hydration is very important. I am very
popular amongst my patients. They all like these diets. I also feed them
gourmet gold when they are in the practice with us.
- Do you
get paid by that company for the marketing you are doing right now?
- No but I
definitely have to talk to them, you are right. I like it because its iodine content
is very low. It barely reaches what they actually made need. And all cats love
it! I wonder if they put something addictive in it! Cecilia Villaverde told me
that it is a very balanced diet so I have no I am very happy to recommend it.
- Well,
remind Purina of that % the owe you then…
- Aw, sorry…
I am not sure about marketing being appropriate in your podcasts…
- Haha! It doesn't matter as long as it is very
beneficial for cats. How about cats with renal
disease? We know that cats in an early IRIS stage we will recommend
curative treatment anyway. Do you take any extra precautions you would like to
talk about?
- It is very frequent to see hyperthyroid cats
with chronic kidney disease. The chances of concurrent diseases increase with
ageing. Dr. Peterson created an amazing
formula that allows to predict the likelihood of chronic kidney disease. It
takes into account the creatinine value, the sdma and the urinary specific
gravity. Hyperthyroid cats have an
increased glomerular filtration rate (GFR). SDMA and creatinine are the values
we use to assess the GFR. We consider IRIS stage 1 when creatinine reaches 1.6mg/dl.
A creatinine of 1.5 mg/dl is already suspicious in a hyperthyroid cat. We assume
that the creatinine should be lower than that because of the loss of muscular
mass. The urinary specific gravity (usg) is also relevant (It is also a very
cheap test! I do not understand how some
vets do not measure it!) Even though is not the most specific test, it is the
most sensitive. When the specific gravity is below 1035 and we observe polyuria
(PU) and polydipsia (PD)… then we must suspect occult chronic kidney disease! Before
discussing this with Peterson, I assumed PU/PD was a normal finding in hyperthyroidism.
However he made clear that we should not assume that it is only triggered by
alterations in the thyroid gland. Regardless the type of therapy (pharmacological,
surgical or medical) GFR drops when euthyroidism is achieved, but CREA never
increases more than one IRIS stage. You never find a cat whose creatinine goes
from 1.5 up to 7 mg/dl. It may go from 1.5 to to 2.3 mg/dl. But should we treat
cats with renal disease for hyperthyroidism? The answer is absolutely YES!
Hyperthyroidism is perpetuating the renal disease and damaging the kidney. We
treat first the hyperthyroidism and, after that, we manage the renal disease
(the associated hyperphosphatemia and hypertension, etc): they become renal
patients. We then have to follow the IRIS recommendations.
It has already been demonstrated
that treating with methimazole first is not necessary. In first place, we can
predict the likelihood of renal disease using the formula we spoke about above.
It has been demonstrated that both cats with and without subclinical azotemia have
the same prognosis with curative treatment. If we don't treat these cats in an
early stage of renal disease we contribute to the kidney dysfunction.
However cats with more advanced
renal disease such as cats in an IRIS stage III or IV, need a more careful
approach. These cats are going to have a short life expectancy anyway. In these
cases it may be better not to consider a curative treatment. Do the owners really
want to pay for the radioiodine treatment when is not the hyperthyroidism what
is going to determine the life expectancy of those cats? I avoid treating cats
with creatinine above 2.5 mg/dl because after treatment it usually increases up
to to 3.5 or 4 mg/dl.
- Do you
then take the CREA values into account when you work out the dose of I131?
- Yes, in
those cats with CREA values just below 2.5 mg/dl you need to be cautious. The
same way the same way hyperthyroidism increases the glomerular filtration rate
and euthyroidism normalises it, hypothyroidism reduces the glomerular
filtration rate. Hypothyroidism will cause a deficient glomerular filtration
rate that is detrimental to the kidneys. And in these cases the increase in
creatinine may be much greater. These cats need levothyroxine supplementation.
- So which
other factors do you take into account when you were work out the amount of
radioiodine? You probably have a formula…
- There are
three different ways. You can use a fix dose as it gets done in UK: 4 millicuries per cat
regardless the hyperthyroid state. In the second method considers doses between 3 and 4 millicuries based on T4 levels. There is a third method where doses are estimated according to scintigraphy results and I131 uptake by the thyroid. Dr Peterson
implemented this protocol a very long time ago. It takes into account
the T4 and the TSH levels (I always say that the formula we use should have Dr
Peterson's name. But he doesn't want to listen to me because he's a very humble
man!) and uses human medicine as a reference. We take into account the
severity of the symptoms, the hyperthyroid state, the duration of the
disease... It is not the same to treat a cat that has been hyperthyroid for 3
years, as treating a cat that has just been diagnosed. Hyperthyroidism becomes
more severe as time goes by. I personally also reduce the radioiodine dose when
I see that occult renal disease is likely, as it is done in human medicine. On
the other hand, if I consider that
hyperthyroidism is the greatest contributor to the loss of quality of
life, I may increase the dose
We also do scintigraphy before
the treatment with the aim of measuring the volume and the function of the
thyroid, by visualising the percentage of technetium uptake. This helps to
estimate the initial dose. Then we monitor the uptake with a Geiger monitor 24
and 48 hours later. That way we find out the real uptake from the specific
amount we inject.
- Oh yes!
I think you mentioned this earlier on, when you explained what the Geiger
monitor was used for.
- Exactly.
The optimal uptake is between a 20 and a 30%. E.g if a cat has an uptake of 8%
and I have calculated an initial dose of 1.8 millicuries, I will have to
increase it up to 2.3 millicuries. However if there is an uptake of 45-50% (what
happens in many hyperthyroid cats) I will reduce the initial estimated dose. The
difference between different methods can be observed in the results. Our dose
range generally varies between 1.5 and 6 millicuries. If we administer 4 to all
cats, in some cases this will be too little and in some cases it will be too
much. If we administer an excessive dose we will trigger iatrogenic
hypothyroidism. This way we only have a 2-3% of chances of iatrogenic clinical
hypothyroidism (low total T4 & high TSH), what is very good compared to the
40-50% caused with other methods.
- That is a
significant difference!
- Yes, it
is. Regarding subclinical hypothyroidism (normal T4 & high TSH), when these
cats show an unexpected increase in creatinine we also supplement with
Levothyroxine. We find this issue in 20 to 30% of our patients. With other
methods the total percentage of iatrogenic hypothyroidism (clinical and
subclinical) is between 50 and 60% of the cats, more than half of them.
- OK, we
will have to repeat this podcast in English to help getting the message across! When do we have to start supplementing with
levothyroxine after the treatment?
- We have
to supplement all the cats that show clinical hypothyroidism (low T4 & high
TSH). In subclinical hypothyroidism (normal T4 & high TSH) we only treat
when creatinine is above 2. It has been demonstrated that it helps reducing the
creatinine and is beneficial to the kidney function.
Iatrogenic hypothyroidism barely
causes any symptoms. It is very difficult for the owners to recognise it.
Hyperthyroid cats show polyphagia and hyperactivity. After euthyroidism, the
put on weight, stop showing PF and are calmer. This is the same process they
pass through when they become hypothyroid. So it is very difficult for the
owners to recognise it. However we want to preserve the renal blood flow, since
hypoperfusion can cause kidney injury.
- Thank you
so much. I find this information very valuable. Going back to the dose of
radioiodine, I guess that underestimating the initial dose of I131 necessarily
causes a need for a second injection?
- Yes, we
call it persistent hyperthyroidism. There's about a 5% of cats that need a
second treatment.
- ...
which is administered in injectable form.
- Yes we
administer it subcutaneously. In human medicine, it can be administered orally.
However giving a capsule to cat is much more complicated and becomes a health
and safety issue.
- Which
other complications do you see more frequently after I131 treatment apart from
iatrogenic hypothyroidism?
- There is
a difference between treating a benign tumour, such as an adenoma, and treating
a malignant tumour, such as an adenocarcinoma.
We may make a presumptive
diagnosis adenocarcinoma based on scintigraphy. We do not do biopsies. Some tumours
are multifocal, and even resistant to methimazole, because of the massive
production of thyroid hormones. Sometimes these tumours need up to 30
millicuries of I131! Our main goal when we treat adenomas is to destroy the
tumour cells, whilst leaving the healthy tissue intact. However when we treat
adenocarcinomas our main goal is to destroy the whole thyroid gland. Low doses
(1-7 millicuries) do not have a lot of adverse effects. Sometimes they may show
temporary or permanent hoarseness. But that's not that important…
- Somebody
should steal your voice for a few days… then you let us see what you think!
- J The main problem with
high doses of I131 is thyroiditis. We are talking here about really large tumours,
sometimes even greater than 10 cm3. They may even invade the thorax. I imagine
it as a huge incandescent mass that must burn once you treat it! They may show
with fever and anorexia. These cats have to stay with us for a couple of weeks.
In cases of benign adenomas usually three or four days is enough. Some of our patients
have had a bad time, but it does not happen frequently. We opened our practice
in 2016- by the way on Monday we will treat our cat number 100!- and we only
have seen 4 adenocarcinomas. Two of them did not have any problem at all and
went home without further complications. A third cat showed a bit of fever and
mild hyporexia but responded well to NSAIDs. However the fourth cat… she came
from Israel... I have now more grey hairs thanks to that kitty! Everything went
fine but the anorexia was terrible. She even needed an oesophagostomy tube
because she did not want to eat at all. However she is perfectly fine now.
- What a great
success! 100 successfully treated hyperthyroid cats!
- Yes,
indeed. We are actually writing a paper for the Journal of Feline Medicine and
Surgery.
- I guess that will not be the last one. I guess
you are collecting a lot of interesting data. 100 cats is quite a large sample when
it comes to feline medicine. Our studies always seem to be based on small
samples.
- Yes,
indeed! We are now measuring the blood pressure and the proteinuria. We measure
these parameters before the treatment, on the day of admission and 6 months
after the treatment, when they come back for the follow-up scintigraphy. Dr.
Peterson also got me involved in a new study about ultrasound measurements of
muscles. This is a very important parameter because some hyperthyroid cats have
a normal body condition score but a very poor muscle condition score. I am very
happy that many practitioners have now the habit of measuring the body condition
score. And as well as the urinary specific gravity it is very cheap! Measuring
muscle condition score is the third cheap thing that we can measure and it may
have prognostic value. We are studying how cats get their normal muscle condition
back after achieving euthyroidism. There is a study from the University of
Tufts showing normal muscular conditions scores in cats and dogs. We use that
study as a reference.
- And how do you manage to keep your family life going at
the same time as all these things that you are telling me about??
- Haha! I think one of these days they are going to tell me
to go away and possibly change the door keys!
- You told me not long ago this was an initiative you had
much later after graduation, when you already had family.
- It is true that sometimes I envy young people without
commitments, who can start a residence or just spend more time abroad! Every
time I go to New York I can only stay there for a week! Very “New Yorkish”… Everything
seems to happen fast over there! I try to go at least once or twice a year. I love
these opportunities of brainstorming and talking about new projects.
- How lucky are Spanish cats! And how lucky are their owners
and also the vets who can listen to you! I feel really lucky to have been able
to talk to you for a whole hour. I have learnt loads. I really, really
appreciate your contribution to my blog.
- It has been good and I also wonder where do you get your
time from, now that you have embarked in La Gatera! I find it is a very nice
project!
- It is fun! I am learning a lot. That is basically why I do
i!
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