Disorders of the Pituitary Gland in Cats
The pituitary gland is located near the center and bottom of the brain. It produces a number of critical hormones that control many parts of the body, including several other endocrine glands. Because of this central role, it is sometimes called a “master gland.” A variety of different conditions can be caused by pituitary disease or tumors. The specific illness and signs depend on the cause and the area(s) of the pituitary gland that is affected.
Cushing disease, also called hyperadrenocorticism, is caused by too much cortisol. Cushing disease is rare in cats. In most affected cats, the cause is a pituitary tumor, although an overactive pituitary gland or a tumor of the adrenal gland itself are also possible causes.
Cats with Cushing disease are generally middle-aged or older. The most common signs include excessive thirst, increased urination, and increased appetite. These signs are frequently seen because cats with Cushing disease also tend to have diabetes mellitus that is resistant to insulin. (Thus, the signs develop as a result of the diabetes mellitus, not necessarily as a result of the cortisol excess seen in Cushing disease.)
The skin of affected cats may be extremely fragile, thin, and easily infected or bruised; this is called feline fragile skin syndrome. Cats may also have an unkempt hair coat, patchy hair loss, muscle wasting, a “potbelly,” and pigmented skin. Some cats may appear listless or depressed due to muscle weakness or to the effects of a large pituitary tumor.
Cushing disease causes substantial weakness and loss of vitality in affected cats. Although therapy is difficult and the outlook is guarded, an attempt is usually made to control the disease because of the overall deteriorating effect on cats with this disorder. Surgical removal of one or both adrenal glands has provided the best results.
In adult-onset panhypopituitarism, the pituitary gland and nearby tissues, including the hypothalamus, are compressed or damaged. This disrupts a number of other hormone-producing glands, resulting in a variety of signs.
Inactive pituitary tumors are one cause of adult-onset panhypopituitarism. They are extremely rare in cats, usually developing in older animals. The tumor may become quite large before it causes obvious signs or death. All breeds appear to be equally affected. Other conditions, infections, or injuries that lead to destruction of pituitary tissue can also cause panhypopituitarism.
Affected cats are often depressed and uncoordinated, and may lose weight. Occasionally, they show a change in attitude, do not respond to people, and tend to hide. In chronic cases, the cat may become blind because the growing pituitary tumor puts pressure on the optic nerves. Animals with panhypopituitarism appear dehydrated despite drinking more water. Cats may urinate in large volumes and use areas other than the litter box.
External beam radiation therapy may reduce the pituitary tumor size and improve the signs in some cats, but the experience using this kind of treatment is limited for cats with large pituitary tumors. The outlook is poor.
Despite its name, diabetes insipidus is not related to the more commonly known diabetes mellitus, and it does not involve insulin or sugar metabolism. Diabetes insipidus is caused by problems with antidiuretic hormone, a pituitary gland hormone responsible for maintaining the correct level of fluid in the body. It occurs rarely in cats; when seen, it tends to affect kittens or young adults. (For a more detailed discussion of Diabetes Insipidus, see Disorders of the Pituitary Gland in Dogs : Diabetes Insipidus.)
Feline acromegaly is caused by a tumor of the pituitary gland that secretes growth hormone. It occurs in cats 8 to 14 years old and appears to be more common in males. These tumors grow slowly and may be present for a long time before signs appear.
Because this disease causes diabetes mellitus, signs of diabetes such as increased thirst, urination, and appetite are present. In addition, signs of excess growth in the legs, paws, chin, skull, and other parts of the body may be seen. In particular, weight gain in cats with uncontrolled diabetes mellitus is a key sign of acromegaly. The heart, kidneys, liver, and endocrine organs are also larger than normal. Insulin levels in the blood are dramatically increased. Feline acromegaly should be suspected in any diabetic cat that has severe insulin resistance.
Signs and laboratory abnormalities can help determine a diagnosis of acromegaly, but the most definitive diagnostic test is computed tomography (CT) or magnetic resonance imaging (MRI) of the pituitary region.
Radiation treatment probably offers the greatest chance of successful treatment, but disadvantages include the slow rate of tumor shrinkage (more than 3 years), the possible development of hypopituitarism, cranial and optic nerve damage, and radiation injury to the hypothalamus.
The short-term outlook in cats with untreated acromegaly is fair to good, using various medications to treat signs. However, because this does not address the cause of the condition, the longterm outlook is relatively poor. Most cats die of congestive heart failure, chronic kidney failure, or signs related to the growing pituitary tumor.