Acromegaly in Dogs

The pituitary gland is an endocrine gland located at the base of the brain. Endocrine glands secrete hormones directly into the bloodstream; they are ductless glands. The production of somatotropin by the pituitary gland usually slows down considerably at adulthood. Growth plates usually close when the dog reaches one year of age. Growth plates are the areas of growing tissues near the end of large bones, which are replaced by solid bone at maturity. The excess production of somatotropin in an adult dog causes unproportioned growth.

When the word acromegaly is broken down; the prefix “acro” means extremities of the body and “megaly” means irregular enlargement. Acromegaly is also referred to as hypersomatotropism. The Saint Bernard breed is believed to be genetically predisposed to acromegaly. Acromegaly is most commonly seen in unsprayed females.

Acromegaly in dogs is an endocrine disorder. The disorder triggers the pituitary gland to overproduce somatotropin, a growth hormone (GH). The increased secretion of somatotropin causes the abnormal overgrowth of bone, soft tissue and internal organs. Acromegaly in dogs may also be caused by the excessive secretion of somatotropin by hyperplastic mammary glands.

Symptoms may include:

• Swollen mammary glands
• Polyphagia - excessive hunger
• Polydipsia - abnormal thirst
• Weight gain
• Tissue swelling of the face and abdomen
• Facial, limb and skin hypertrophy
• Excessive urination
• Noisy breathing
• Stiffness/rigidity
• Excessive panting
• Prominent skin folds
• Enlarged tongue
• Gap in teeth due to the jawbone continuing to grow
• Enlargement of the gums
• Hair loss
• Pale gums
• Lethargy
• Diabetes
• Hyperthyroidism (overactive thyroid gland)
• Arthritis (inflammation of the joints)
• Heart failure

• Pituitary gland tumor
• Hyperplastic mammary glands 
• Long term use of progesterone; progestogen is usually prescribed to older dogs, infertile bitches and aggressive dogs
• Predisposed genetic abnormalities in the anterior pituitary gland inherited in the Saint Bernard breed

The veterinarian will want to go over your companion’s  medical history.  Let the veterinarian know if your dog is on any medications or supplements.  

The veterinarian will perform a physical exam and assess your dog’s overall health condition.  He may take the patient’s weight, temperature, pulse and blood pressure. The veterinarian may listen to your dog’s heart with a stethoscope and will also check the patient’s teeth and gums.

He may suggest a thyroid stimulating hormone test (TSH) and an ACTH (hormone produced in the pituitary gland) stimulation test. A growth hormone test will evaluate pituitary gland function and will also help determine excess growth hormone. 

Other diagnostic blood tests that can help narrow down the diagnosis are prolactin, cortisol, follicle-stimulating hormone (FSH) and luteinizing blood test (LH). A complete blood count and a serum chemistry test may also be recommended.

A magnetic resonance imaging (MRI) scan can help visualize the brain and can determine if there is a pituitary tumor. Abdominal and skull x-rays may also be suggested to rule out neoplasia.

Canines on progesterone medications or medications that have progesterone in them should stop taking the medicine.  Intact females may require an ovariohysterectomy (removal of the ovaries). The patient may be prescribed somatostatin, a growth hormone inhibitor.

Dogs with pituitary tumors or mammary tumors may be started on chemotherapy and/or radiation therapy. Chemotherapy uses medications to destroy cancer cells. Radiation therapy uses photons, gamma rays and electrons directed on the tumor.  Radiation therapy is meant to destroy the cancer cell’s ability to divide and grow.  Radiation therapy is given in small amounts over 2 to 5 weeks. Surgery may also be suggested.  

Patient diagnosed with diabetes mellitus will need to have daily insulin injections.  The veterinarian may also suggest a diet low in protein and phosphorous.

If progesterone medication triggered acromegaly in the patient, once the medication is stopped, the recovery prognosis is good.  Dogs that have pituitary tumors or mammary gland tumors have a more guarded prognosis.  

Owners of dogs that undergo surgery will be given specific postoperative instructions for the care of their pet. Many dogs will need to have an E- collar on until the sutures are removed.  Exercise will be limited to small walks which will increase per the veterinarian’s instructions.  Your dog will be prescribed antibiotics to prevent infection; additionally pain medication and anti-inflammatory drugs may be given.  

Follow-up visits will be necessary to monitor the patient’s progress.  The retaking of bloodwork and an MRI scan may be required.  Sutures will be removed by the veterinarian.