No hyperthyroidism per se can’t cause kidney disease in cats but it seems that some treatments for hyperthyroidism can reduce kidney function.
Dr Bruce Fogle in his book Complete Cat Care writes, “Chronic kidney failure does not occur as a direct effect of hyperthyroidism, but the two diseases often occur together simply because they are both common in older cats”.
Hyperthyroidism increases the blood supply to the kidneys which can might improve their function. The doctor also says that if both diseases are present in your cat it may be wise not to treat the hyperthyroidism. This leads me nicely to an article about the relationship between feline hyperthyroidism and renal function. It is published on the World Congress 2006 web page.
The article tells me that studies have found that the treatment of hyperthyroidism can reduce the functioning of the kidneys.
Azotemia describes a condition in which kidneys have been damaged by disease or injury and the kidneys are no longer able to get rid of enough nitrogen waste (abnormally high levels of nitrogen-containing compounds are in the blood). A study mentioned on the webpage that I refer to tells us that “approximately 30% of hyperthyroid cats are azotemic after therapy of [for] hyperthyroidism”.
It appears that when treating a cat for hyperthyroidism careful tests need to be carried out to decide the best therapy and avoid damaging the kidneys. They also state that the relationship between hyperthyroidism and kidney disease in cats is complex. It is difficult to diagnose with precision cats that are suffering from chronic renal failure and hyperthyroidism.
I’m not qualified to go on and dig around further because it is highly complicated and I don’t want to mislead people. I would just suggest that if anybody reads this article they might treat it as a flag or a warning that if your cat does have hyperthyroidism you should ask your veterinarian whether the treatment will have any effect on kidney function. Just raise that possibility and discuss it. I hope that you find the article useful in that sense.
Hyperthyroidism, as mentioned, is a common disease in older cats. It describes a condition in which the thyroid glands produce too much of the hormone thyroid. The thyroid glands are enlarged (they are in the cat’s neck). Most often the problem is caused by a benign tumour. Thyroid hormones control the cat’s metabolic rate so if there’s too much thyroid in the body the rate increases and the cat burns up energy and loses weight despite eating a lot.
Chronic kidney failure (CRF) is also very commonplace in elderly cats. The kidneys lose their ability to filter and remove waste products. The cause of kidney failure in older cats is unknown. Statistically 20 percent of cats over 15 years of age have chronic kidney failure. It is 300% more common in domestic cats than in domestic dogs. Before you can tell that a cat has chronic kidney failure up to 75% of kidney tissue has already been destroyed.
Sources other than stated: Dr Bruce Fogle DVM.