Acromegaly is long-term excessive secretion of growth hormone from a tumor of the pituitary gland in the brain. In felines, these tumors grow slowly and may be present for a long time before you notice any changes in your cat. The medical term for acromegaly is hypersomatotropism.
Clinical Findings
Feline acromegaly tends to occur in older (8-14 years) cats and appears to be more common in males. Most cats will first display signs of uncontrolled diabetes mellitus, namely, drinking water excessively, urinating excessively, and eating much more than usual. Unlike cats with long term uncontrolled diabetes, cats with acromegaly will gain lean body mass. Cats with acromegaly (which we like to call AcroCats!) often have enlargement of their kidneys, liver, and endocrine organs. In addition, some cats may get enlargement of extremities, body size, jaw, tongue, and forehead. The paws, chin, and skull may especially become enlarged. The heart can enlarge, heart murmurs develop, and congestive heart failure can occur late in the disease course. About half of cats with acromegaly will get a condition called azotemia where kidney dysfunction will cause nitrogenous wastes to accumulate in the blood. All cats with acromegaly have an impaired ability to process glucose and are resistant to the action of insulin and thus have diabetes mellitus. Generally, cholesterol levels and liver enzyme levels will be elevated. Protein is often present in the urine.
Diagnosis
Feline acromegaly should be suspected in any diabetic cat that has severe insulin resistance (insulin requirement more than 20 units per cat day). Diagnosis can only be made by laboratory tests performed by your veterinarian. Tests that your veterinarian will perform include measurement of increased plasma growth hormone or insulin-like growth factor 1 (IGF-1) concentrations. Serum IGF-1 concentrations are often dramatically increased in acromegalic cats. Currently, the most definitive diagnostic test is computed tomography (CT) of the pituitary region of the brain. Results of computed tomography, combined with the exclusion of other disorders that cause insulin resistance (hyperthyroidism, hyperadrenocorticism) and clinical signs and laboratory abnormalities, support a diagnosis of acromegaly.
Treatment
Medications used in people includes the use of dopamine agonists, such as bromocriptine, and somatostatin analogs (octreotide). Treatment with octreotide has not been successful in acromegalic cats. Radiation therapy probably offers the greatest chance for success.
Prognosis
Diabetes mellitus can be controlled with daily injections of insulin. Mild heart disease can be managed with medications such as diuretics and vasodilators. The longterm prognosis of the cat with untreated acromegaly is not very good. Eventually, most cats die of congestive heart failure, chronic renal failure, or from growth of the pituitary tumor. The longterm prognosis may improve with early diagnosis and treatment.
References
Axiom Veterinary Laboratories Limited:
http://www.axiomvetlab.com/EF%207-0%20UC.html#Introduction%20to%20Feline%20Acromegaly
FelineDiabetes.com, "Acromegaly: A Case History and Discussion
http://www.felinediabetes.com/Acromegaly.htm
The Merck Veterinary Manual:
http://www.merckvetmanual.com/mvm/htm/bc/40508.htm
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