Elderly cats often have overactive thyroids
Sadie is a ten-year-old cat I've been seeing a lot recently: she developed the most common hormonal condition seen in pet cats.
The condition is hyperthyroidism, or an overactive thyroid gland, caused by a small tumour on one of her thyroid glands. The thyroid glands are small glands, half way up the neck, on either side of the windpipe, one on the left and one on the right. They produce thyroid hormones, which act like the accelerator pedal in a car, giving animals energy and enthusiasm for life. Over-production of this hormone causes an animal to behave is if their accelerator pedal is permanently pushed down to the floor.
This is an astonishingly common problem in cats: in one recent study of cats over the age of ten being blood sampled, 21% had elevated thyroid hormones. The average age at the time of diagnosis is 13 years, and while the precise cause has not yet been identified the following are known to be risk factors: use of cat litter, eating a diet consisting of more than 50% moist food, and eating a fish-based, moist diet.
Sadie is a typical example: there had been a gradual, subtle change in her habits and behaviour. She was a calm cat who used to spend much of her time sitting around, as if reflecting on the world. She stopped doing this, and was more likely to be seen rushing about the place than sitting down quietly.
A change of behaviour like this can happen for many reasons, including social issues (such as a new cat in the area) so it was difficult to read anything into it.
Her owner brought her to see me for a different reason: she had started to bring up her dinner several times a week. Prior to this, she had never vomited. Her owner knew that it was not 'normal' for a cat to have digestive upsets so often.
When I examined her, there were two physical findings that made me suspect hyperthyroidism. First, her heart rate was over 200 per minute, which is much faster than normal. And second, I could feel a small hard bump on the underside of her neck, like a small frozen pea beneath the skin. The lump was in the same location as her thyroid gland.
I was almost certain that Sadie had a tumour on her thyroid gland. Thyroid tumours in cats are usually benign, but because they produce extra thyroid hormones there's a profound impact on the cat.
I took a blood sample to measure Sadie's thyroid hormones and the result confirmed what I'd suspected. Her thyroid hormone levels were four times higher than normal.
The good news was that hyperthyroidism is easy to treat. There are four possible forms of treatment, with the best choice depending on the cat's individual situation.
The simplest answer is a daily tablet to suppress hormone production. If an owner feels happy giving their cat tablets, then this can work well. However, it does mean daily tableting for the entire life of the cat, and there is a small risk that the thyroid tumour could end up becoming malignant, so it's worth considering other treatment options.
Surgery to remove the small thyroid tumour is another possibility. This can be costly, but once it has been done, there is no longer a need for daily tablets, so it can make sense as a long term cost effective answer. The surgery can often be done by a local vet with no need for a referral to a specialist centre.
The third option is radiation treatment. The cat goes to a specialist centre where a dose of radioactive iodine is given; this selectively destroys thyroid tissue, reducing the amount of thyroid hormone production. The cat has to be kept at the treatment centre for several weeks, as they will be emitting radiation from their body, so there is a potential risk to humans if allowed in close contact with people. This option is more costly and more complicated, logistics-wise.
The final treatment option, suitable for some indoor-only cats, is to feed a prescription-only low iodine diet which naturally reduces thyroid hormone production. However if a cat gets food or water from any other source, this does not work.
Every cat is different: it's important to discuss a treatment plan with the vet before deciding. In Sadie's case, surgery was the chosen option: she needed tablets for a few weeks first, to slow her racing heart and to make the anaesthetic safer, but she then came through the surgery well, and the tablets could be stopped. Within a few weeks, she had stopped vomiting, and she had started to behave more like her former self. And at a deeper level, her general metabolism will have returned to normal, so she will go on to have a happier, healthier old age.
It's likely that there are hundreds of undiagnosed hyperthyroid cats out there, with their owners just thinking that it's normal for older cats to change in subtle ways as they grow older. The truth is that while some old age changes are normal, if a cat develops a thyroid tumour, the signs will get progressively worse and worse if the cat is not diagnosed and treated. Affected cats lose weight, and become restless, anxious, agitated creatures.
Many elderly cats could have longer, happier, healthier lives if this condition was diagnosed and treated. A visit to the vet and a blood test is all that's needed. If your older cat has changed, think about it.
New Ross Standard