Destruction of the Pituitary Gland in Dogs

The pituitary gland is a small gland located at the base of the brain. Despite its size, the pituitary gland produces a number of different hormones that regulate other endocrine glands and control many functions throughout the body. Many important hormones are produced here, including thyroid stimulatory hormone (TSH), adrenocorticotrophic hormone (ACTH), growth hormone (GH), and antidiuretic hormone (vasopressin). Because it affects so much of the endocrine system, the pituitary gland is sometimes called the master gland. Tumors are the most common cause of pituitary destruction in older dogs, but an injury or infection can also destroy tissue. Most pituitary tumors are benign and slow growing, however, large tumors put pressure on the hypothalamus, the brain area next to the pituitary gland that regulates many important pituitary functions. A condition called panhypopituitarism results. This is a reduction the in normal levels of many pituitary hormones. Tumors can also affect other parts of the brain and even cause blindness. Panhypopituitarism may also develop in younger dogs due to a birth abnormality. Puppies with this problem, are small and stunted with very little hair, and usually have a shortened life span. This is most common in German Shepherds, but some other breeds also have a similar problem. Many secondary conditions can develop with panhypopituitarism, including hypothyroidism, Addison’s disease (hypoadrenocorticism), and diabetes insipidus. Pituitary tumors may also secrete hormones, most commonly ACTH which causes Cushing’s disease (hyperadrenocorticism). Surgical removal of a pituitary tumor is difficult and rarely attempted. In adult dogs, tumors sometimes shrink with radiation treatment, but in young dogs there are few treatment options.

The pituitary gland is a very important part of the endocrine system that regulates hormone production in many other glands. In dogs, the pituitary gland can fail to form properly, or it can be destroyed by a large tumor, injury, or infection. This leads to a condition called panhypopituitarism, a reduction in many different pituitary hormones.

Take your dog to see a veterinarian if you notice any of the following symptoms.

In puppies

• Slow growth after about 2 months of age
• Gradual hair loss
• Small sexual organs
• Adult teeth do not come in
• Stunted size

In adult dogs

• Depression
• Attitude change/less friendly toward people
• Lack of coordination
• Weakness
• Weight loss
• Excessive drinking
• Increased urination
• Blindness (in severe cases)

Types

There are two types of panhypopituitarism.

• Juvenile-onset panhypopituitarism (pituitary dwarfism) – either the front portion of the pituitary gland fails to develop, or the puppy has a cyst or tumor from birth
• Adult-onset panhypopituitarism – usually due to a tumor, more common in middle-aged or older dogs

• Some breeds are more prone to juvenile-onset panhypopituitarism (German Shepherd, Spitz, Miniature Pinscher, Karelian Bear Dog)
• Benign tumors causing adult-onset panhypopituitarism are found equally in all breeds
• Some breeds have a higher rate of ACTH producing tumors that lead to Cushing’s disease (Boxer, Dachshund, Boston Terrier)
• Infection or injury that destroys part of the pituitary gland can also cause adult-onset panhypopituitarism

The veterinarian may suspect destruction of the pituitary gland based on your dog’s symptoms. Blood and urine test often show abnormalities related to hormone imbalances. The veterinarian may order tests to evaluate the functionality of other endocrine glands and determine the source of the problem. Many secondary conditions associated with the destruction of the pituitary gland can also be caused by an adrenal or thyroid tumor, so this is an important step. An ACTH stimulation test or a dexamethasone suppression test (DST) is often ordered to diagnose Cushing’s disease and determine if it is caused by the pituitary gland or the adrenal glands.

Pituitary tumors causing panhypopituitarism are usually large enough to be diagnosed with magnetic imaging. X-rays and ultrasound will be taken and the vet may order a CT scan or MRI for clearer imaging. Other x-rays may be needed to check for metastasis or to evaluate the potential of tumors in other glands. The veterinarian will need to know your dog’s age and breed. Past medications can also be relevant since long term steroid use is often related to hormone imbalance.

Puppies with pituitary dwarfism are given various hormone treatments. Thyroid replacement hormone and growth hormone can help to make up for the lack of normal stimulant hormones from the pituitary gland. Canine growth hormone has not been manufactured, so dogs are usually given human or pig GH. This is effective in some dogs, while others have adverse reactions. Progesterone can help some puppies grow and regain normal hair growth, but there are significant side effects with this treatment.

Surgical removal of pituitary tumors is difficult and risky, so it is rarely recommended. Radiation treatment can help to shrink some tumors in dogs with adult-onset hypopituitarism. Radiation will be given in several doses over a 2-5 week period. Dogs often have minor skin reactions at the time. Long-term serious side effects are possible, so discuss the necessity and risk of this treatment with your veterinarian. 

Hormone treatment and other medications may be necessary for secondary conditions. Dogs with Cushing’s disease, Addison’s disease or hypothyroidism will often need lifelong medication. Dogs in an Addisonian crisis may need emergency treatment with intravenous fluids and electrolytes. 

Puppies with pituitary dwarfism are given various hormone treatments. Thyroid replacement hormone and growth hormone can help to make up for the lack of normal stimulant hormones from the pituitary gland. Canine growth hormone has not been manufactured, so dogs are usually given human or pig GH. This is effective in some dogs, while others have adverse reactions. Progesterone can help some puppies grow and regain normal hair growth, but there are significant side effects with this treatment.

Surgical removal of pituitary tumors is difficult and risky, so it is rarely recommended. Radiation treatment can help to shrink some tumors in dogs with adult-onset hypopituitarism. Radiation will be given in several doses over a 2-5 week period. Dogs often have minor skin reactions at the time. Long-term serious side effects are possible, so discuss the necessity and risk of this treatment with your veterinarian. 

Hormone treatment and other medications may be necessary for secondary conditions. Dogs with Cushing’s disease, Addison’s disease or hypothyroidism will often need lifelong medication. Dogs in an Addisonian crisis may need emergency treatment with intravenous fluids and electrolytes.