I know, it’s kind of a funny sounding word. But if you have a diabetic cat that your vet just can’t seem to stabilise, it’s definitely not a laughing matter. Acromegaly has recently been found to affect up to a quarter of diabetic cats in the UK, many more than previously thought, so it’s worth talking about. It’s also probably underdiagnosed, which means your vet may not think to look for it, so if you’ve been told that your cat’s diabetes is particularly difficult to control, read on!
What is acromegaly?
The name acromegaly actually comes from human medicine, because in people, it causes abnormally large hands, feet and facial features. Although you can see similar signs in cats (a broad face with a protruding lower jaw and larger than normal feet), it’s much less common so another term you may see used is ‘hypersomatotropism’ which literally means an excessive production of growth hormone. It’s caused by a benign (ie, unlikely to spread to other tissues) tumour on the tiny pituitary gland, situated at the base of the brain. The pituitary gland secretes lots of useful hormones that control all sorts of functions in the body, but in this case it’s growth hormone produced in huge quantities by the growing tumour that causes the problem. The majority of affected cats are males unlike in dogs, where acromegaly is usually caused by changes in the mammary gland and is therefore seen almost exclusively in females that haven’t been spayed.
What’s the connection between acromegaly and diabetes?
Too much growth hormone floating around the body decreases its sensitivity to insulin, which is the hormone that controls sugar metabolism. If the body doesn’t respond very well to insulin, the blood sugar gets too high and the cat becomes diabetic. This causes the typical diabetic clinical signs of drinking a lot and urinating a lot, along with a greater than average appetite. Despite the big appetite, a normal diabetic cat will often lose weight until their disease is controlled. However due to the other effects of growth hormone, cats with concurrent diabetes and acromegaly tend to gain weight even if their diabetes isn’t well controlled. And because the acromegaly makes insulin less effective, it often takes huge doses of insulin injections to bring the diabetes under control (some normal cats can be controlled on 1-2 units of insulin twice a day, while cats with concurrent acromegaly may require up to 35 units twice a day!). Even with that much insulin, they may never be well-controlled and are much more likely to suffer from frequent episodes of ketoacidosis, a dangerous condition that occurs when the body is simply overwhelmed by too much blood sugar.
What are some of the other signs of acromegaly?
In addition to the effects on sugar metabolism mentioned above, excessive growth hormone also causes a rise in something called insulin-like growth factor-1 (IGF-1). This IGF-1 causes excessive tissue growth, not just in the face and feet mentioned above, but also in internal tissues such as the throat (causing breathing problems) and the heart (causing a murmur). It may also cause the internal abdominal organs to feel bigger on the vet’s exam but this can be really difficult to detect. Cats with acromegaly also seem prone to high blood pressure, and rarely, the tumour itself can grow so large that it causes changes in behaviour or other neurological signs. Interestingly, it can also affect the joints so arthritis symptoms can be seen. Sadly, the effects on the heart can sometimes be so severe that the cat develops congestive heart failure.
How is it diagnosed?
Despite the fact that acromegaly is quite common in cats, there is currently no simple test to prove that a cat has the disease. Your vet may start to suspect it if your cat is gaining weight despite the fact that their blood sugar is not under control, or if your cat requires larger than average doses of insulin to stabilise. If acromegaly is suspected, there is a blood test for the IGF-1 peptide, however the results of this test can be misleading especially in the early stages of the disease. A more expensive and complicated but perhaps more accurate test would be a CT or MRI scan of the brain, which may be able to show the tumour on the pituitary gland directly, but even this isn’t a perfect test. It is important to try to distinguish between acromegaly and another condition called hyperadrenocorticism which can have similar symptoms and even look the same on a scan.
How do you treat it?
So diagnosing acromegaly is difficult, and unfortunately treating it isn’t any easier. Because it’s caused by a tumour, the choices are the same as many other tumours and include an intensive (and expensive) course of radiotherapy or specialist (ie, also expensive) surgery to remove the tumour itself. With treatment, the tumour can shrink and the diabetes itself can even resolve, along with preventing some of the other common side effects of the disease. However there isn’t currently any way of predicting how well a particular cat will respond to treatment or for how long the recovery will last. If no treatment for the pituitary tumour is given, the only other option is to continue treating the resulting diabetes as best as you can, with large doses of insulin and frequent check-ups with the vet to discuss progress and quality of life, similar to cats that were never diagnosed in the first place. But it’s worth finding out if your cat has the disease, as you’ll be more prepared to diagnose and treat the other side effects such as joint pain, high blood pressure and heart disease. Cats with concurrent acromegaly and diabetes don’t tend to respond as well to routine treatment and may be euthanized sooner as a result, although some cats may do well despite their disease. Because we have only recently realised how common the condition is, new testing and treatments are being developed as we speak and hopefully our options will improve as time goes on.
If your diabetic cat isn’t responding well to their treatment and you think they may have acromegaly, you should speak with your vet about it, bearing in mind that many of us don’t know much about the condition because it used to be considered so rare. Diagnosis and treatment aren’t easy, but they are possible and could potentially result in a happier, healthier cat. Hopefully a few years from now the story will have an even happier ending!