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Acromegaly (Hypersomatotropism) in Cats

Also known as 'pituitary gigantism' or 'hypersomatotropism',  acromegaly is a rare disease caused by an over production of the growth hormone (GH). The cause is usually a functional benign pituitary tumour (adenoma).

Acromegaly typically affects middle-aged to male domestic shorthair or longhair cats. The median age is 11 years.

What are the signs of acromegaly in cats?

Excess of the GH causes enlargement of the extremities (head, feet, jaw, scull) soft tissues (tongue, heart, kidneys, liver) and increased muscle mass and abdominal enlargement. The most obvious signs appear to be on the head with a protruding mandible (lower jaw) and wide head.

Uncontrolled diabetes is a common finding in cats with acromegaly, as GH is a modulator of insulin sensitivity, therefore symptoms associated with diabetes may be observed. These may include, polyuria/polydipsia (increased drinking and urination) as well as polyphagia (increased appetite).

Other symptoms of acromegaly may include:

  • Cardiovascular abnormalities such as systolic heart murmur, hypertrophic cardiomyopathy, and congestive heart failure. These may present as lethargy, difficulty breathing, weakness.

  • Increased space between the teeth as the jaw increases in size.

  • Thickened skin and dull fur.

  • Painful joints.

  • Weight gain.

  • Enlarged kidney.

  • Enlarged liver.

  • Enlarged endocrine organs.

  • Central nervous symptoms such as head pressing, circling and behaviour changes.

How is acromegaly diagnosed?

Your veterinarian will perform a complete physical examination of your cat and obtain a medical history from you. Acromegaly may be suspected in a cat who is persistently hyperglycemic despite daily insulin injections, especially if it is accompanied by other symptoms such as weight gain,  [1] along with ruling out other conditions which also cause uncontrolled diabetes is important (hyperthyroidism, hyperadrenocorticism).

Some tests he may wish to perform include:

  • Increased blood growth hormone or insulin-like growth factor (IGF-1) concentrations.

  • CT scan of the pituitary gland to look for a mass on the pituitary gland.

  • Thoracic radiographs may reveal an enlarged heart.

  • Signs of congestive heart failure, pleural effusion, and pulmonary edema in advanced cases.

  • Baseline tests such as complete blood count, urinalysis, and biochemical profile. The most common findings are hyperglycemia (high blood glucose), high cholesterol and high phosphorous levels and glucosuria (glucose in the urine). If the disease has progressed, other findings may include protein in the urine, elevated liver enzymes and azotemia.

How is it treated?

There is no successful way to permanently treat acromegaly in cats and managing the clinical signs to provide your cat with a good quality of life. This may include:

  • Radiation therapy to shrink the tumour. Side effects are common with this treatment.

  • Somatostatin analogs and dopamine agnostics to inhibit the GH production or reduce GH levels in the blood.

  • Controlling diabetes with larger doses of insulin and dietary changes, such as low protein, low phosphorous foods.

  • Controlling mild heart failure with diuretics and vasodilators to prevent pulmonary edema and pleural effusion.

Long term prognosis is not favourable, with heart or renal failure eventually causing death.

References:

[1] The Cornell Book of Cats

Also see:

Cat symptoms