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Growth Hormone: Does your cat have acromegaly?

The current generation of pet owners is very smart. They are very much involved in the health of their pets. Pet owners google everything, then their veterinarians have to debunk some of the things they have found, or some of the things they were told by their breeders. I actually don't mind, in fact, since I love to educate, I will go into discussing with the owners that every heart murmur in an adult dog is considered significant enough for diagnostics, that grain-free diets have an association with the development of heart disease, that yes, you bought an adorable Frenchie - who will also develop allergic skin disease, and that every little dog, especially Yorkie's are going to have trouble with their teeth.

Not many pet owners will know about acromegaly. The only time that the general practice veterinarian diagnoses acromegaly is when they have a diabetic feline patient that they can't seem to get good control over their blood sugar.

What is Acromegaly?

Acromegaly in cats is infrequently diagnosed, but is the existence of a pituitary tumour that secretes an excessive amount of growth hormone. However, acromegaly is not just a condition in cats, it is found in people, and some of the research in people we extrapolate to animals - especially in the case of joint and bone pain, since our cats cannot really tell us much about the pain they are experiencing. Acromegaly is more common in male cats and is found in older patients. Features of cats with acromegaly can include: enlargement of extremities, forehead and jaw.

Physical changes associated with feline acromegaly include increased body weight, a broadened face, enlarged feet, protrusion of the mandible (prognathia inferior), increased interdental spacing, organomegaly, and a poor coat. VIN Feline Acromegaly

Testing for Acromegaly in Cats

It was the jaw of our clinic cat Tiger that had me thinking about acromegaly as a potential cause of his lengthened jaw, but also his limping, polydipsia and polyuria. He is a polydactyl kitty who is also overweight, so the limping could be early arthritis - that so far has not contributed to any radiographic changes. Remember that the absence of radiographic changes in joints does not rule out arthritis - the inflammation of joints.

Tiger's senior blood screening was unremarkable - showing normal creatinine and blood urea nitrogen (BUN), normal T4, normal serum glucose - ruling out renal (kidney) disease, hyperthyroidism and diabetes mellitus as causes of his PUPD. His urine specific gravity was 1.012 (isosthenuric), with negative proteinuria. We decided since he is a clinic cat to tack on the extra cost of an IGF-1 test (insulin like growth factor 1 hormone).

Tiger's result was high-normal at 91 nmol/L (696 ng/ml; with the reference range being up to 92 nmol/L). It is thought that acromegaly is an underdiagnosed condition.

So, now we have possible acromegaly in our clinic cat. The next step would be imaging - MRI is the best imaging modality for diagnosing a pituitary tumour since it is soft tissue (over a CT scan). MRIs are not inexpensive, but the question that we ask ourselves, and of our pet owners, what would we do with this information if we found it?

Treatment for Acromegaly in Cats

Since acromegaly is an underdiagnosed condition, it is not frequently treated. It is thought that radiation therapy (performed in the U.S. at NC State College of Veterinary Medicine) and surgical hypophysectomy (performed in the U.K. and U.S.) are the suggested treatment instead of medications.

More importantly, since the increase in growth hormone can lead to insulin resistance, monitoring for glucosuria (urinalysis) and hyperglycemia (blood sample) would be important in cats where you have found clinical and laboratory suspicion of acromegaly as likely this makes these cats predisposed to insulin resistant diabetes mellitus.

Management of Acromegaly

Weight control: This is really important for most cats. Acromegaly cats will gain weight easily. Weighing the cat regularly and regulating the caloric intake will be important. This is also important for relieving pressure on their joints.

Pain control: I already mentioned that people are painful when they have this condition, so adequate pain medication is important. We can't say for sure that our cat patients get headaches, but people with acromegaly do. If the cat's kidneys are functioning well, then you may be using a non-steroidal anti-inflammatory, and perhaps something for neuropathic pain (Gabapentin), since people with acromegaly experience neuritis. It is thought that pressure on the nerves occurs with the increase in connective tissue, bone or joint synovial fluid.

Somatostatin treatment: So far, the medical management of reducing growth hormone and insulin like growth factor has variable results of success in our feline diabetic patients, which may be due to differences in somatostatin receptors within feline pituitary tumors. Yet, I am curious if you diagnose Acromegaly prior to the development of diabetes mellitus, would it decrease the likelihood of that cat developing diabetes if treated early - just a thought really. Here's a fairly recent article on the use of a somatostatin (Pasireotide) to inhibit growth hormone in diabetic felines, which I feel is promising.

For Tiger, we have him on Gabapentin twice daily, and now that his diet is being controlled, he has not been experiencing any diarrhea, so we can add back an NSAID (meloxicam). He had no radiographic evidence of arthritis - but since we see him limping, we give him the benefit-of-the-doubt that he has some pain component. The DVM team has decided not to pursue advanced imaging, since this would require referral and at some point we have to draw a line - again what would we do with that information (not sending him to the states for surgery). Finally, we will need to do regular screening for insulin resistance, looking for glucose loss in the urine.

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