The information contained in this article is provided for educational purposes only and is not intended to replace veterinary advice.
Please consult with your vet for further information.
Long thought to be quite rare in cats, there is increasing understanding that Acromegaly, or Hypersomatotropism, is more prevalent than thought. One study has shown that one in three diabetic cats in North America suffers from acromegaly induced diabetes¹; another that one in four diabetic cats in the UK is suffering from the same².
Acromegaly should be considered as a possible cause of difficult to regulate and high dose diabetic cats.
What is Acromegaly?
Acromegaly is an endocrine disease caused by a tumour in the pituitary gland in the brain which secretes excessive amounts of growth hormone (GH). The tumour is usually benign and very slow growing.
GH is responsible for regulating growth: it helps make kittens grow and helps maintain normal body structure in adults. It also plays a role in regulating the metabolism of protein, fat and glucose.
GH is controlled by the hypothalamus, another gland in the brain, and normally is released in pulses every few hours. In a cat suffering from Acromegaly, the tumour causes GH to be released in greater amounts and more continuously, flooding the body with high levels of the hormone.
This video from the Diabetic Remission Clinic, part of the RCV (Royal Collage of Veterinarians) in the UK shows where the tumour is situated:
What is the result of excess Growth Hormone (GH) on the body?
The excess GH caused by the tumour has both a direct and an indirect effect on the body.
GH is an insulin antagonist and affects the sensitivity of cells to insulin. High levels of GH lead to insulin resistance as they block the normal action of insulin: insulin stops working as the key that opens the cells to let the glucose enter and be used as a source of energy. As a result, glucose builds up in the blood.
In addition, GH helps to break down stores of carbohydrates. The high levels of GH lead to breaking down more and more of those stores: that in combination with the insulin resistance leads to high blood glucose levels and Feline Diabetes.
It is the indirect effect of GH, however, that causes most of the damage to the body.
GH stimulates the liver to produce Insulin-Line Growth Factor 1, or IGF-1. This is one of its normal functions. IGF-1 stimulates and regulates body growth, affecting almost all parts of the body.
The high levels of GH caused by Acromegaly result in high levels of IGF-1 being produced, and growth becomes uncontrolled:
• Bone and cartilage production is increased leading to such changes as broader faces, protruding lower jaws and/or clubbed/enlarged feet
• Growth and enlargement of all organs occurs: the kidneys, the heart, the liver and endocrine organs such as the pancreas are all affected
• Soft tissues such as the tongue and soft palate may also become enlarged
Clinical Signs of Acromegaly
Acromegaly is a disease that progresses slowly, and symptoms will take some time to start showing. Some cats will show very few symptoms, even when the disease is established. It usually occurs in cats that are around 8-14 years old, and males seem to be more commonly affected with it than females.
One of the first signs or symptoms of Acromegaly is difficult to control diabetes and insulin resistance leading to very – or even extremely – high doses of insulin being needed to control blood glucose levels.
Unlike most diabetic cats with poorly controlled blood glucose levels who lose weight, cats with Acromegaly will often (if not always) gain weight.
Difficult to control Feline Diabetes requiring higher than usual doses of insulin and weight gain vs. the usual weight loss seen in cats with uncontrolled blood glucose levels are signs that your cat may have Acromegaly, and should be tested for the disease.
Other clinicial signs, which may not be apparent immediately, and which will not necessarily develop in all Acromegalic cats, are:
• Cardiomegaly: heart enlargement leading to a particular type of hypertrophic cardiomyopathy, or HCM. The cat can develop a galloping rhythm or heart murmurs. Congenital heart failure can develop in the later stages of the disease.
• The liver is almost always enlarged (heptomegaly).
• The pancreas and kidneys will increase in size also: in advanced stages Chronic Renal Disease (CRD) may develop.
• In advanced stages of the disease, a “bowling ball stomach”: an enlarged belly due to the increased size of the internal organs.
• The face can broaden and both the face and neck can be visibly enlarged due to excess skin; the skull thickens also, if only visible with x-ray or imaging exams.
• The lower jaw can grow, leading to gaps between the upper and lower canine teeth.
• The paws become bigger, or “clubbed” due to the growth of the bones and the tissue in the paws.
• The tongue and soft palate may grow, leading to difficulty in breathing.
• Spondylosis (spinal problems) can occur, leading to degeneration of the spine or bone spurs forming.
• Some cats may experience their back legs growing, giving them a “rabbit appearance”.
• Hypertension may occur, if there is some disagreement as to whether this is truly linked to Acromegaly or not.
• Neurological signs, such as seizures, may occur, but are usually rare.
These photos, from the RVC (Royal Veterinary College) website show photos of a cat before and after the onset of Acromegaly: the broadening of the face and growth of the jaw can be clearly seen:
Again, not all cats with Acromegaly will display all of the above symptoms – some may show external symptoms such as the widening face and club paws… others will not.
In addition to the above, Acromegalic cats will display classic signs of uncontrolled Feline Diabetes such as excessive drinking and urinating and ravenous hunger.
There is not one single test for Acromegaly that confirms 100% the presence of the disease.
The exam most commonly used is the IGF-1 serum test.
IGF-1 levels are more stable than GH levels, as GH is secreted in pulsations. The IGF-1 test will usually therefore provide more reliable results than GH testing. The GH test is also recent and not available in all countries. It can, though, be useful to help confirm the IGF-1 result and increase accuracy of the diagnosis in countries where it is available.
False positives or negatives may occur with the IGF-1 tests. A cat that has recently started insulin may have low IGF-1, but the factor may increase significantly with insulin therapy. Conversley, a non-acromegalic cat that has been on insulin for a long time, may show higher than usual IGF-1 levels vs. a non-diabetic cat. Malnutrition, if your cat has not been eating, may also result in lower than normal results. Kidney or liver issues may also have an impact.
Norms should take into account the cat’s age, and may differ between laboratories. Regardless, anectodal evidence from groups of people with cats with Acromegaly have tended to show that cats can be acromegalic at levels under those that are usually considered simply borderline by the veterinary profession.
Once high IGF-1 and/or GH have been established, the diagnosis may be confirmed by radio imaging: CT and MRI scans.
These scans measure and look at the pituitary gland and will usually show the tumour. Both exams are expensive and do require anethesia. While rare, there can be false negatives with them also: the tumour does not always show in the scan. Such scans are necessary before some treatements. They may not be worth the cost or stress on your cat if you are not pursuing some of the treatments outlined below.
If you do not have the imaging examines done, even if your cat is “just under” or borderline vs. the IGF-1 norms the lab provides you with, if he is continuing to exhibit signs such as the need for high doses of insulin, ravenous hunger, and/or weight gain despite high blood glucose levels, you should assume that even without a definitive test result, your cat probably does have Acromegaly.
Treating Acromegaly consists of trying to treat the fundamental disease itself but also treating the effects of the conditions that result from Acromegaly.
Treating Acromegaly itself
There are three basic methods of treating Acromegaly itself:
• Surgery: removal of the tumour and pituitary gland or hypophysectomy.
• Radiation therapy – either traditional treatment or Stereotactic Radiation Therapy (SRT).
• Medical treatment using pituitary inhibitors. While unsuccessful when used for cats in the past, recent research is making huge advances on this subject.
Unfortunately, all treatment options are very expensive and all but traditional radiation therapy are only available in a handful of very few highly specialised vet hospitals at this time. Not all treatments are available in all regions of the world.
The barriers of cost and availability mean that for a number of people, treating the Acromegaly itself is simpy not possible. If that is the case, there are nonetheless many things that you can do to treat the effects of Acromegaly (see the next section) that will truly help your cat.
While Hypophysectomy is commonly used to treat Acromegaly in humans, it requires a highly specialised veterinarian surgeon and team, and this treatment has only been performed by a handful of hospitals.
A Hypophysectomy removes the tumour and the piturary gland. The operation is performed by going through the roof of the mouth.
In Europe, Hypophysectomy was first performed in the Netherlands at Utrecht University – the only country to perform this surgery on cats for a number of years. Today, it is also available at the RCV in London. In the US it can be performed in Washington State (it was previously available in California). It is also available in Japan and has very recently started to be performed in Australia, in Melbourne.
The advantage of the surgery is simply that is does absolutely remove the root cause – the tumour. So, the cat is “cured” of Acromegaly once the tumour is removed.
Most cats see their diabetes cured also, with a return to normal numbers and insulin no longer needed.
In addition, improvement to some organs damaged by acromegaly may be seen, especially concerning damage to the heart.
Your cat will however need on-going hormone replacement treatment following the surgery.
Costs are usualy less than those related to SRT – the actual surgery itself is less expensive than may be thought given the highly specialised team necessary. Costs increase because of the long hospital stay of 10-15 days after the surgery that is usually required and the costs regarding various tests around the surgery. The on-going for life hormone replacement costs also need to be taken into account. Advanced imagery (MRI/CT Scans) are necessary to pinpoint the position of the tumour and make certain it can be removed.
Radiation Therapy: Traditional and SRT
1) Traditional radiation therapy is the most widely spread treatment available for cats. The goal of radiation therapy is to reduce the production of GH to levels that are no longer significant and to reduce the size of the tumour itself.
In general, it is more successful in reducing the size of the tumour than in reducing the GH levels. Traditional radiation therapy is given over a series of treatments, requiring multiple hospitalisations (and use of anesthesia) over a number of weeks.
2) SRT uses imagery to delivery radiation to a very targeted area and so can pinpoint the tumour itself. As is the case for hypophysectomy, it is available in a very limited number of hospitals.
In the US, Colorado State University is a leader in the domain. Yonkers in New York is another. The Ontario Veterinary College at the University of Guelph offers SRT. Currently, SRT is not available in Europe.
Usually only one course of treatment , over a few days, is given.
SRT is far more precise than general radiation therapy as it does allow directing radition precisey to the tumour itself. The course of therapy is much shorter, and your cat does not have to be put under anethesia the number of times necessary for traditional radiation therapy. SRT is though, very expensive. MRI/CT Scan exams are also necessary before SRT treatment in order to pinpoint the exact position of the tumour, adding to the total cost.
A major disadvantage of radiation therapy – whether traditional or SRT – is that results can range from none at all to a full response, may take months to start showing – if they do at all – and may or may not be permanent. There is no way to know how an individual cat will react.
Medical treatment using pituitary inhibitors (specifically targeting somatostatin receptors) has been used successfully with humans – but cats have not reacted to the same. Recently published research (results published the same time this is written, in May 2015³) is showing a potential breakthrough for cats with the use of fast acting Pasereotide, a newer somatostatin analog that decreases the secretion of GH.
The results of the study are promising, with a decrease in IGF-1 and in the amount of insulin needed. A longer term study is underway.
Studies using long-lasting Paseriotide are also going on; however, this medication is not yet approved for veterinary or human use in many countries, if it was approved for human use in the EU in November 2014. The fast-acting Pasereotide is approved in more countries.
A study published in February 20174 concluded that: “Pasireotide LAR (long-lasting) is the first drug to show potential as a long-term management option for cats with HS” (Hypersomatotropism).
Signifor or Signifor LAR (long-lasting) are the brand names in Europe for Paseriotide. Authorisation for veterinary use of Signifor LAR is pending.
In general, blood glucose levels will often be similar before and after treatment: the amount of insulin needed to control the levels, though, is usually very much reduced, and some cats will even go into remission and no longer need insulin therapy.
It is very important that you are monitoring your cat’s blood glucose levels, that you do reduce your scale with the treatment, and continue to adjust as needed.
At the moment, the cost is higher and the results are less good than for surgery. It is a very promising advance in dealing with Feline Acromegaly though. Should the continued research confirm the initial findings, it will provide a treatment far more widely available than either hypophysectomy or SRT treatment. Hopefully continued research along this line will help cats more in the future!
If available and possible for you, Hypophysectomy is currently the best option: when successful (the entire tumour can be removed), it cures Acromegaly, and certain organs will even improve vs. the damage caused by the disease. Many cats will no longer need insulin, their diabetes will also be cured. Your cat will need to be on hormone replacement therapy for life, though.
Paseriotide, if a newer treatment, is probably the best second choice – again, if your vet is able to prescribe that. It does greatly reduce the GH and IGF-1 secretions, and will therefore very much slow and control the progression of the disease. In terms of the related diabetes, it should lead to very much reduced levels of or even no more insulin needed. It is however, very expensive today.
Of the two radiation possibilities, SRT is preferable to normal radiation, which has lower results and requires multiple sesssions of anethesia. SRT is far more targeted and precise, so has less side effects. The problem with both SRT and simple radiation therapy is that it can takes months to see if there is any improvement, and results can range from none at all to being very successful…. and may or may not be permanent.
Treating the effects of Acromegaly
The numerous side effects of Acromegaly do need specific help and treatment:
• Agressively increase insulin as needed and use a rapid insulin along with your normal longer acting insulin to help bring your cat’s blood glucose levels under control. Note: rapid insulin should only be used with the help and advice of your vet. The same Tight Regulation protocol used on Diabetic Cat International for non acromegalic works very well for cats with acromegaly and will help you control your cat’s BGs.
• Treat the pain: an Acro Cat is usually suffering from significant pain as a result of the uncontrolled growth of bone and tissue – you need to talk to your vet about appropriate analgesics to help. One commonly prescribed analgesic that does seem to help many Acro cats is Gabapentin.
• Treat the hunger that goes with Acromegaly – let your cat eat what it wants.
• Treat the heart problems with the medications indicated by your vet: ACE inhibitors such as Enalapril will usually be prescribed by your vet. Other medications that may be prescribed include Aspirin, Sprironolactone, Pimoban and Benazepril. Note: Aspirin is toxic for cats: it is VERY important to not give more than what your vet has prescribed.
• Treat eventual kidney problems as you would normally with kidney disease: ACE inhibitors (Benazepril – Forketor in Europe or Lotensin in the US ), fluid therapy (Sub-Q fluids), B-Complex vitamins, antacids, and phosphorous binders if needed. Important: remember that due to the heart conditions you need to be very careful about the amount of fluids you administer
Even if you are unable to have treatment for the Acromegaly itself done, being aware of the side effects and treating them if and as they do occur will help your cat both in terms of quality of life and in length of life. You can make more than a difference in helping your cat with the above!
There are advances concerning the treatment of Feline Acromegaly being made every day. It is now being understood that it is behind a significant number of Feline Diabetes cases. With that understanding, we can hope that more research on treatment will continue!
If you live in the UK (or Europe), one of the leading Acromegaly specialists in the world is Dr. Stijn Niessen, who also runs the RVC Diabetes Remission Clinic. It would be very worthwhile having your vet contact the clinic for more help and information on their on-going research into, and treatment of, Acromegaly. Dr. Niessen was involved with the latest research on Paseriotide and is also behind the introduction of Hypophysectomy in the UK. There are various research studies going on at different times at the RCV Feline Diabetes Remission Clinic and it is possible that your cat could enter one of those studies. The FD Remission Clinic can help provide your vet with information on the use of Paseriotide.
The Facebook page can be found here: Diabetes Remission Clinic
The main RCV site is here: Royal Veterinary College – Internal Medicine
Please do post on the DCI forum. One of the Senior Members here has had two Acro cats. She is a wealth of information on the subject and can help you!
And we can – and will – help you regulate the diabetes caused by Acromegaly with Tight Regulation on forum!
Additional Reading and Resources:
Last updated February 2017
¹ Berg, R.I., Nelson, R.W., Feldman, E.C. Kass, P.H, Pllard, R & Refsal, K.R. (2007): Serum insulin-like growth factor-I concentrations in cats with DM and acromegaly. Journal of Veterinary Internal Medicine 21, 892-898
² Niessen, S.J., Petrie, G. Guadiano, F., Khalid, M., Smyth, J.B., Mahoney, P. & Church, D.B. (2007a): Feline acromegaly: an underdiagnosed endocrinopathy? Journal of Veterinary Internal Medicine 21, 899-905
³Scudder, C.J., Gostelow, R., Forcada, Y., Schmid, H.A., Church, D. and Niessen, S.J.M. (2015), Pasireotide for the Medical Management of Feline Hypersomatotropism. Journal of Veterinary Internal Medicine. doi: 10.1111/jvim.12608
© Diabetic Cat International 2014-2017