Excessive Growth Hormone (Somatotropin) in Cats
Acromegaly in Cats
Acromegaly is a rare syndrome resulting from the excessive production of the growth hormone somatotropin by tumors in the anterior pituitary gland of adult cats. Clinical signs of this syndrome are a result of the hormone's direct catabolic (breaking down) and indirect anabolic (building up) effects.
The anabolic effects, meanwhile, are mediated by somatomedin C (insulin-like growth factor I), which is secreted by the liver in response to growth hormone stimulation. The excessive levels of somatomedin C, however, promote protein synthesis and growth in a variety of tissues such as the bone cartilage, soft tissues, especially in the head and neck region. Eventually these abnormalities in joint cartilage growth and metabolism alter normal joint biomechanics, which can lead to degenerative joint disease.
Somatotropin also fights the action of insulin, which eventually causes pancreatic cell exhaustion and permanent diabetes mellitus.
Symptoms and Types
Initially, signs relate to unregulated diabetes mellitus. As the disease progresses, signs of heart failure, kidney failure, or central nervous system abnormalities caused by tumor expansion develop, including:
The hypersecretion of the growth hormone somatotropin by an anterior pituitary tumor.
You will need to give a thorough history of your cat’s health to your veterinarian, including the onset and nature of the symptoms. He or she will then perform a complete physical examination as well as a complete blood count, biochemistry profile, urinalysis, and electrolyte panel.
Other diagnostic exams include X-rays, echocardiogram, and CT (computed tomography) and MRI (magnetic resonance imaging) scans. CT and MRI scans are used to locate the pituitary mass. X-rays, meanwhile, often reveal an enlarged heart and sometimes fluid in the lungs, especially if left-sided congestive heart failure has already developed. And an echocardiogram will confirm heart abnormalities.
A radioimmunoassay for plasma somatomedin C is available at Michigan State University -- which can confirm the elevated plasma levels associated with acromegaly -- but this is often impractical.
Often, the goal is to treat and control the secondary diseases that develop following prolonged growth hormone hypersecretion (e.g., diabetes mellitus, heart failure, and kidney failure). However, there have been some successful attempts at treating the acromegaly.
In one study, for example, cobalt radiotherapy was used in which six out of seven acromegalic cats showed permanent or temporary resolution of insulin resistance following therapy. In another case, the surgical removal of the pituary tumor by freezing (cryohypophysectomy) also showed success. The cat slowly regained normal plasma somatomedin C levels and the diabetes mellitus resolved after two months.
Consult your veterinarian for the best course of treatment for your animal.
Living and Management
Your veterinarian will schedule follow-up appointments with you to treat your pet's secondary complications, as necessary. Unfortunately, cats are usually euthanized or die because of complications associated with congestive heart failure, kidney failure, and/or progressive central nervous system signs (seizures, etc.). Reported survival times following diagnosis range from 4 to 42 months, with a median of 20 months.
A medical condition involving excessive thirst
Excessive eating or swallowing
An in-depth examination of the properties of urine; used to determine the presence or absence of illness
The gland that is found at the bottom of the brain whose job is to maintain appropriate levels of hormones in the blood
The group of processes that involve the use of nutrients by the body
Term used to refer to the front of the pituitary gland; can be found at the bottom of the brain and is responsible for the secretion of certain hormones that deal with growth and other bodily functions.
The hormones that stimulate growth of the body
A hormone created by the pancreas that helps to regulate the flow of glucose
In veterinary terms, used to refer to the front of the body.
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