Acromegaly

Also known as: Hypersomatotropism

Introduction

Acromegaly results from chronic excessive secretion of growth hormone in the adult animal. It has been recognised in dogs and cats, but the aetiology of the disease in both species is completely different.

In dogs, acromegaly results after administration of progestational compounds for the suppression of oestrus in intact female dogs. There is excessive secretion of growth hormone by the mammary cells under the influence of exogenous progesterone. Therefore it occurs most commonly in intact older female dogs.

In cats, acromegaly is caused by a functional growth hormone-producing tumour of the anterior pituitary. These tumours grow slowly and may be present for a long period of time before onset of clinical signs. Feline acromegaly occurs most commonly in older male cats.

The disease is characterised by overgrowth of soft tissues, bone and viscera, and insulin-resistant diabetes mellitus.

Clinical Signs

Polyuria, polydipsia and polyphagia are the most common presenting signs due to the uncontrolled diabetes mellitus.

Weight gain is a key presenting sign in cats.

Conformation changes include: large head, prognathism (long mandible), enlarged interdental spaces, large paws.

Lameness: due to arhtropathies and proliferation of cartilage

Enlarged abdomen: due to organomegaly: heart, kidney, liver and tongue

Skin changes: thickened, oedematous skin with prominent folds on the neck and face, hypertrichosis, hyperpigmentation, thick, hard nails.

Inspiratory stridor due to thickened mucosa

Cardiomyopathy in 45% of cats which can lead to congestive heart failure seen as weakness and dyspnoea.

Renal failure in 50% of cats

Reproductive disease in dogs such as pyometra, mucometra and mammary gland nodules

In cats, the pituitary itself can rarely cause central nervous system signs such as head pressing, dullness and anorexia.

Diagnosis

In dogs there will be a history of progesterone treatment, dioestrus or diabetes mellitus.

In cats, the history will be consistent with uncontrolled diabetes mellitus.

Clinical signs relate to a change in physical appearance, which can be documented by using old photographs of the animal.

Haematology, biochemistry and urinalysis: there will be hyperglycaemia and glucosuria. Other findings include: hyperphosphataemia, hypercholesterolaemia, hyperproteinaemia and increases in liver enzymes.

Insulin-like growth factor-1 levels: this allows an indirect assessment of growth hormone levels. A value greater than 200 is strongly suggestive of acromegaly.

Radiography: these will show cardiomegaly in 86% of cats, hepatomegaly, renomegaly. There may be pleural effusions and oedema. Bony changes include spondylosis, periarticular periosteal reactions.

Ultrasonography: echocardiography will reveal ventricular hypertrophy in the cat.

Adrenal and thyroid testing: these should be performed to rule out other causes of uncontrolled diabetes mellitus. Values should be normal in acromegalic cats.

CT or MRI: these provide a definitive diagnosis in cats, and may reveal a pituitary tumour. A mass, combined with the clinical signs, enables a GH-secreting pituitary tumour to be the most likely cause.

Treatment

In dogs, progesterone treatment should be withdrawn, and intact females should be ovariohysterectomised.

Growth hormone concentrations should normalise and soft tissue abnormalities should resolve.

The prognosis is good.

In cats, no successful therapy has been reported.

Radiation therapy: can be considered, and has lead to good results in some cases. However the tumour commonly recurs after cessation of therapy.

Medical therapy: increased levels of insulin will be required to manage the diabetes mellitus.

Dopamine agonists have been tried to reduce circulating GH levels, but response has not been shown to be good.

Heart disease should be managed with diuretics and beta blockers, and renal disease by feeding a low protein, low phosphorus diet.

Prognosis is good in the short term and most will do well for 1-2 years. However in the long term it is grave, and cats are usually euthanised due to congestive heart failure, renal failure or the expanding pituitary tumour.

Acromegaly Learning Resources
Flashcards Test your knowledge using flashcard type questions	Veterinary Dentistry Q&A 07

References

Norsworthy, G. (2011) The Feline Patient John Wiley and Sons

Merck and Co (2008) Merck Veterinary Manual Merial

Pasquini, C. (1999) Tschauner's Guide to Small Animal Clinics Sudz Publishing