Hypopituitarism in Dogs
Several hormones are produced by the pituitary gland, any one or more of which may be lacking. The resultant condition, hypopituitarism, is associated with low production of hormones that are produced by the pituitary gland, a small endocrine gland located near the hypothalamus at the base of the brain. Of these hormones, some of the more clinically significant ones are the thyroid-stimulating hormone (TSH); the adrenocorticotropin hormone (produced by the anterior pituitary gland that stimulates the adrenal cortex); the luteinizing hormone (stimulates secretion of sex steroids); the follicle stimulating hormone (secreted by the gonadotropes in the anterior pituitary gland); and the growth hormone (GH). Hypopituitarism can also result from the destruction of the pituitary gland by a cancerous, degenerative, or anomalous process.
This disorder is known to occur on average in dogs around the ages of two to six months. There appears to be some breed disposition, appearing more frequently in German shepherds, Carnelian bear dogs, spitzes, toy pinschers, and weimaraners. In German shepherds and Carnelian bear dogs the cause has been linked to a simple autosomal recessive genetic trait.
The symptoms of hypopituitarism can vary depending on which hormones are lacking, and which body function is being affected by the deficit. For example, lack of luteinizing hormones can result in sexual abnormalities such as abnormally small genitals, and GH deficiency can result in lack of appropriate growth or dwarfism. If the gland is being affected by cancer or tumor, the affected dog may be experiencing pain in its head (with consequential head-pressing), or visual problems. Other symptoms include:
- Mental retardation, manifested as difficulty in house-breaking
- Thin, hypotonic skin – having less than normal tone or tension, as of the muscles or arteries
- Hair loss on the trunk (alopecia)
- Cutaneous hyperpigmentation – darkening of an area of the skin
- Delayed dental eruption
- Head-pressing due to pain in the head from a tumor
- Cystic Rathke's pouch – a benign cystic tumor that results from remnants of remaining fetal tissue
- Isolated GH (growth hormone) deficiency
- Pituitary tumor
You will need to give a thorough history of your dog's health, growth, behavioral development, onset of symptoms, and possible incidents that might have preceded this condition, such as trauma to the head. A complete blood profile will be conducted, including a chemical blood profile, a complete blood count, and a urinalysis. Blood tests are the most reliable method for diagnosis of this condition.
Standard blood test results may show increased levels of eosinophilia (white blood cells), lymphocytosis (disease of the lymph glands), hypophosphatemia (phosphorus deficiency), or hypoglycemia (low blood sugar). Other laboratory tests will test the levels of hormones in the bloodstream. Your veterinarian will want to have your dog brought in for a morning blood draw in order to measure basal levels of TSH and prolactin. Another blood test, called a dynamic test, measures hormone levels after injection of a hormone stimulating substance. This can be used to check levels of ACTH and GH. The results of these tests generally are the best indicators for hypopituitarism. Visual imaging techniques, primarily using X-ray, can be used to check for the presence of a tumor or cyst in the vicinity of the pituitary gland.
Management of hypopituitarism is usually conducted on an outpatient basis. Growth hormone supplements will be administered to your dog three times weekly for 4–6 weeks, and repeated if necessary. Tumors of the pituitary gland can be surgically removed in some cases, but the prognosis is generally not favorable.
Living and Management
Your veterinarian will schedule follow-up visits in order to monitor your dog's blood and urinary glucose concentration. Growth hormone supplementation will be suspended if glucosuria (an abnormal condition of osmotic diuresis due to excretion of glucose by the kidneys) develops, or if the blood glucose is more than 150 mg/dL.
Your dog's skin and haircoat should improve within 6–8 weeks of initiating growth hormone and thyroid supplementation. Generally, in the case of low GH levels, there is no increase in stature because the growth plates have usually closed by the time a diagnosis has been made. Unfortunately, because many of the hormones that are affected by pituitary disorders are essential for the overall health, the long term prognosis for hypopituitarism is poor.
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