Observations on the Progression of Feline Acromegaly (v2)

Acromegaly results from excess growth hormone produced by a tumour of the pituitary gland in the brain.  The tumour can be cancerous (adenocarcinoma) or non-cancerous.  These notes discuss the key locations where the effects of growth hormone can be seen, and more insidiously, where they can not.

Bony growth:  Some bones seem susceptible to continued growth in the adult cat while others do not.  

1. The lower jaw sometimes grows, resulting in a gap between the upper and lower canine teeth.  A lot of growth can result in the cat having some difficulty eating, but it rarely seems to get that advanced.  

2. The small bones in the paws also grow, resulting in the classic big paws.  They may become painful over time.

3. In a few cats, the back legs have grown longer giving the cat a rabbit-type appearance.  

4. The skull becomes thicker, but this is seldom visible except on x-ray.  Some cats exhibit symptoms of headache.

5.  Spondylosis may develop in the spine with both degeneration and bone spurs forming.  This is extremely painful and results in decreased mobility.  It may also lead to reluctance to use the litter box due to pain in squatting or defecating.

Soft tissue growth:  Nearly all of the tissue of the cat seems susceptible to growth.

  1. The face, tongue and neck may become visibly enlarged.  Some owners describe the appearance as puffy.  The excess tissue in the neck requires particular attention, especially during anaesthetic.  It may be difficult to tube the cat and require a smaller tube than the vet would normally expect.  This is an important point to stress to the vet if the cat is going to have an anaesthetic.  This tissue growth may also cause the cat to snore or breathe audibly and can also result in difficulty swallowing.
  2. On the paws, extra tissue will grow along with the bones so that some cats have very large paws.
  3. All of the internal organs will become enlarged, although not all are affected to the same degree in every cat.  Liver, kidneys, and pancreas are all subject to enlargement leading to the ‘bowling ball belly’ in the advanced stages of the disease.  Chronic pancreatitis is common in cats with acromegaly.  Several cats in the advanced stages have also developed megacolon.
  4. The heart develops a particular type of hypertrophic cardiomyopathy or HCM.  The details are most relevant to a cardiologist, but it is extremely important that owners know that HCM develops as a result of acromegaly.  The cat may develop a gallop rhythm (an extra beat) and clots are a very real possibility with the progression of the heart disease.  Subcutaneous fluids need to be very carefully administered to an acro with advanced HCM.  If kidney disease is also advanced, fluid may accumulate in the abdominal cavity.  This fluid can be drained, although some vets are reluctant to do this.  It is important to pursue draining as a palliative measure if the cat is in distress.

Seizures or epilepsy:  Several of the cats in the acromegaly group have had seizures.  One had three, no treatment, and no repeat.  A few others have required antiseizure medication and have been well controlled.  One cat was not able to be assessed by a neurologist quickly enough and therefore start medication and his seizures progressed very rapidly.  The radiologist at Colorado State University said in an email “In general if there is a large mass in the region of the pituitary OR if there is radiation induced damage there, seizures aren't what we would generally expect.  Most animals with problems here are depressed, circling wide circles, blind, decreased gag reflex.”

In at least one cat, the owner had noticed for some time that the cat responded with a quick twitch to sharp noises and crinkly such as tissue paper.  We do not know the significance of this twitching – perhaps simple coincidence.