By Dr. Becker
Feline acromegaly, also called hypersomatotropism, is an uncommon, though probably underdiagnosed, endocrine-related disease in cats. It's the result of chronic overproduction of growth hormone caused by a slow-growing, growth-hormone-secreting tumor of the pituitary gland. Often, these tumors are present for long periods before the cat becomes symptomatic.
Growth hormone stimulates the production of insulin-like growth factors in several organ systems. Insulin-like growth factor-1 (IGF-1), which is produced by the liver, is thought to be what causes the characteristic appearance of people, dogs, and cats with acromegaly. Kitties with acromegaly often have large bodies, broad faces, enlarged feet, protruding lower jaws, increased spacing between teeth, and a poor coat.
Signs and Symptoms
Acromegaly typically occurs in neutered male cats over the age of eight, in particular, kitties with poorly controlled diabetes. Symptoms of diabetes are often the first signs of acromegaly and include excessive thirst, excessive urination, and increased appetite. Impaired glucose tolerance and insulin resistance are found in all kitties with acromegaly. The disease should be suspected in any cat with severe insulin resistance.
Enlargement of the kidneys, liver, and endocrine organs is common in cats with acromegaly. Enlargement of the heart, heart murmurs and congestive heart failure occur in advanced stages of the disease, as does azotemia, which is an excess of urea or other waste products in the blood as a result of failing kidneys.
Excessive growth of the soft palate and laryngeal tissues can cause respiratory problems and upper airway obstruction.
Neurologic disease in feline acromegaly is rare, but does occur in cases of very large pituitary tumors. Symptoms include lethargy, abnormal behavior, circling and blindness.
Other conditions associated with acromegaly include urinary system pathology and secondary renal failure, and lameness resulting from diabetic neuropathy.
Diagnosing Feline Acromegaly
Unfortunately, no single test exists to diagnose acromegaly in kitties. Many of the results seen in the complete blood counts, serum chemistry profiles and urinalyses of affected animals are associated with diabetes mellitus. These include hyperglycemia, increased liver enzymes, high blood cholesterol, and glucose in the urine.
Serum IGF-1 measurement is the most commonly used diagnostic test for feline acromegaly. However, elevations in IGF-1 concentration alone may not definitively diagnose acromegaly in a cat.
Advanced imaging – a CT scan or MRI – is needed to check for the presence of a pituitary tumor. However, the presence of a tumor alone cannot confirm a diagnosis of feline acromegaly since other tumors of the pituitary gland also cause insulin-resistant diabetes. And the absence of a tumor can't rule out acromegaly, since not every single pituitary mass is identified via MRI or CT scan.
Results of an MRI or CT scan, coupled with the exclusion of other disorders that cause insulin resistance (hyperthyroidism, hyperadrenocorticism), clinical signs and laboratory abnormalities, support a diagnosis of acromegaly.
The traditional treatment for feline acromegaly with the greatest success rate is radiation therapy, which has low rates of morbidity and mortality. Unfortunately, tumor shrinkage using radiation takes years, and there can be significant side effects, including cranial and optic nerve damage, injury to the hypothalamus, and decreased production of pituitary hormones, so I don't recommend this treatment option.
In the short-term, the prognosis for kitties with untreated acromegaly is fair to good. Insulin resistance can be controlled, especially if a species appropriate diet is fed, and mild cardiac disease can be managed. I recommend adding ubiquinol to these cats' diets immediately upon diagnosis. The longer-term prognosis is relatively poor, however. Most cats die of heart or kidney failure or growth of the pituitary tumor. The long-term outlook for cats with acromegaly can often be improved with early diagnosis and treatment.
I have found the best approach to management is organ and nutritional support; early heart and kidney support can make a huge difference in longevity and quality of life, and nutritional support (feeding a species appropriate, low glycemic diet) can make a substantial difference in controlling insulin and blood glucose fluctuations, improving the cat's overall metabolic health.
Feline Acromegaly Is Uncommon, But Also Underdiagnosed
According to dvm360, a recent study in the United Kingdom measured IGF-1 concentrations in diabetic cats. Of the 184 cases, 59 (32 percent) had markedly increased IGF-1 concentrations. Eighteen of the 59 cats underwent pituitary imaging, confirming a diagnosis of acromegaly in 94 percent.
The study illustrates the importance of ensuring that veterinarians remain aware of feline acromegaly so that they may more consistently diagnose and treat these patients.