Cats Are Just Different Part 2: Hyperthyroidism – What To Do About It?

How to tell the Thyroid: “Enough Already!”

In the last post, I went over what Hyperthyroidism is and what it can do to the body.

Now, what are we doing about it.

In the case of Spice, she is in an only-cat household. Since thyroid hormone is made using a molecule of iodine, we can bring the hormone levels back into the normal range by providing only enough iodine to make only the right amount of thyroid hormone. The tumour is still there, and would still make lots of hormone if it could… but by using a prescription diet restricted in iodine (Hill’s y/d), we are starving the tumour’s ability to operate. But this means NO cheating on this diet! Treats can provide enough iodine to let the tumour go right back to full operation.

Diet is not so useful for Kala, though. He lives in a multi-cat household, and his housemates all have various dietary needs. The iodine-restricted diet would not work unless everyone were on it. So, in Kala’s case, we are using a medication called methimazole that suppresses the ability of thyroid cells to make hormone. He will be getting the medication as a Transdermal gel, absorbed through the hairless skin of his ear flap.

The TD Gel has two advantages over pills:

1.  It is easier and less stressful than giving pills twice a day for the rest of the cat’s life
2. Not giving the medication through the stomach decreases the chance of stomach upset.

 

There are still some disadvantages to the methimazole, though: over time, the medication can become less effective; and, some cats will develop an allergic reaction to it and develop an incredibly itchy facial rash (the good news is that the rash goes away when you stop giving the medication).

The definitive treatment for Hyperthyroidism is Radioactive Iodine Therapy. This uses an isotope of iodine, called I(131). Cells making thyroid hormone are the ones “hungriest” for iodine, so they take it up preferentially. The tumour cells are the hungry ones… the normal thyroid gland cells DO listen to the “enough, you can stop!” signal, and so they are dormant. The isotope releases a tiny burst of radiation when it decays, just enough to give the cell that took it up a case of terminal heartburn.

The advantages of Radioactive Iodine Therapy:

1. It is usually curative, getting rid of the tumour completely
2. It even gets thyroid tumour cells living elsewhere than where they belong (the thyroid gland is in the neck, but sometimes there can be some thyroid tissue hiding down in the chest too).

 

The disadvantages of this treatment:

1. It is expensive since you are paying it all at once – medication and follow-up blood tests can add up over time, but then the cost is spread out
2. It requires the cat be away from home in a treatment ward for 2 weeks. While they are in hospital, their kitty litter is handled as radioactive waste (and yet people get this treatment on an out-patient basis and go home to pee in the same sewers as the rest of us – go figure…)

 

Surgery to remove the tumour from the thyroid gland is possible, but this has fallen out of favour with the other options now available.

The take home message is that hyperthyroidism can be managed. If an older cat is getting skinny, don’t assume that it is “just age” – a blood test can shed light on various treatable conditions, including hyperthyroidism.