What links Lurch in the Addams Family, pro-wrestler Andre the Giant, and Jaws from the James Bond film The Spy Who Loved Me? They all suffered from the condition known as acromegaly caused by an excess of growth hormone which gave them their characteristic stature. But acromegaly can also be seen in the veterinary world, in a fairly unexpected group of patients – cats. 

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What causes acromegaly?

As stated above, acromegaly is the name given to the condition in which a patient suffers from an excess production of growth hormone. Growth hormone is secreted from the pituitary gland in the brain and acts to maintain homeostasis, or balance, within the body and between different organ systems. Growth hormone affects nearly every organ in the body and encourages protein synthesis and bone growth. When it acts on the liver, it also stimulates the release of another hormone known as insulin-like growth factor (IGF-1) which works in a similar way.

Unfortunately in cats, the main cause for this increase in growth hormone is a tumour, known as a functional adenoma of the pituitary gland. These tumours are usually benign and slow growing so are not thought of as a true ‘cancer’. 

What are the symptoms of acromegaly?

The symptoms of acromegaly all stem from the impact the excessive levels of growth hormone have on the body. Like humans, affected cats will tend to have a fairly characteristic appearance though it may be harder to appreciate. Typically they will:

  • be on the heavier side
  • have a broad face
  • have large or ‘clubbed’ feet
  • sometimes have a protruding lower jaw
  • have wider spaces between their teeth
  • have a poor hair coat

As well as these primary physical characteristics, there are many potential secondary effects from the growth hormone including

  • respiratory disease
  • heart disease (due to an enlarged heart)
  • renal failure
  • arthritis
  • neurological signs, seen with particularly large tumours.

Interestingly, probably the most common symptom seen with these cases is diabetes, which can often prove difficult to get under control. In fact, it is estimated that up to 25% of diabetes cases have underlying acromegaly. This is because growth hormone is an antagonist of insulin meaning that in presence of high levels of growth hormone, insulin is prevented from promoting glucose uptake into cells, leaving high levels of glucose in the blood (hyperglycaemia) and therefore a form of diabetes. 

How acromegaly is diagnosed

Unfortunately, the most obvious way of diagnosing acromegaly, by measuring the levels of growth hormone in the body, is not available in the UK. We can, however, measure the IGF-1 hormone, though even this is not enough for a definitive diagnosis. At present, the diagnosis of acromegaly comes from a combination of tests and ruling out other conditions. Because the underlying cause is down to a tumour in the brain, advanced imaging such as a CT or MRI scan is required to confirm the presence of a mass, which is then used in conjunction with supporting clinical signs, blood work and a lack of other diagnoses to confirm, as far as possible, a case of acromegaly. 

Acromegaly is thought to be an under-diagnosed condition in the UK, with estimates placed around 1 in 1,000 cats for the UK population. Middle-aged male cats are most at risk. 

Treatment of acromegaly

The gold standard of treatment for acromegaly in cats is surgery to remove the affected pituitary gland, a procedure known as hypophysectomy. This is a fairly new advance in the treatment for this condition, with the first case only recorded in 2010. Subsequent cases have shown a very good success rate and around 70% were no longer classed as diabetic. 

Other options for treatment include:

Radiotherapy 

Good results but multiple general anaesthetics required and may not achieve the same levels of diabetic remission

Medical therapy 

Generally unproven and suggested drugs are extremely costly

Conservative management 

Typically only trying to control the diabetes that is responsible for many of the unwanted symptoms of acromegaly.

Overall, although acromegaly is an uncommon condition in cats, it is one that we, as clinicians, ought to be on the look out for in at-risk patients, as if diagnosed and treated successfully, these cats can return to a fairly normal and good quality of life.

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