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.
For information on AcromegalyTreatment, please see the following page
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