Hyperadrenocorticism is an abnormal condition caused by prolonged exposure to excessive levels of glucocorticoids. There are three forms of hyperadrenocorticism which vary in cause but exhibit similar clinical signs.

Pituitary-dependent hyperadrenocorticism (PDH) is the most common form accounting for almost 80% of the cases and is associated with a pituitary tumor. Because of a pituitary abnormality there is excessive production of adrenocorticotropic hormone (ACTH) which results in excessive secretion of cortisol by the adrenal gland.

Adrenal-dependent hyperadrenocorticism (ADH) is responsible for approximately 20% of the hyperadrenocorticism cases and is usually the result of an adrenal tumor. Adrenocorticol abnormalities cause the adrenal gland to produce excessive levels of cortisol, independent of the pituitary production of ACTH.

Iatrogenic hyperadrenocorticism is the result of excessive or prolonged administration of steroids and not a result of a pituitary or adrenal abnormality. Once the steroids are discontinued the symptoms of iatrogenic hyperadrenocorticism will cease.

Symptoms
Hyperadrenocorticism is a slow progressive disease the result of chronic exposure to excess cortisol levels. Most dogs with hyperadrenocorticism do not exhibit visible signs of acute illness that the owner would immediately take note of such as vomiting, diarrhea, seizures, pain, or bleeding. Because the clinical signs are slow to develop, often dogs will exhibit a symptom of the disease for 1 to 6 years before a diagnosis is made.

The most commonly noticed symptoms are increased water intake (polydipsia) and increased urination (polyuria). Dogs with hyperadrenocorticism can increase their water intake by 2 to 10 times their normal amount. Because of the increased water intake the dog will urinate more frequently, the owner may notice that the dog begins to urinate in the house.

Increased appetite is another symptom but one that may be overlooked by the owner. Generally owners associate a decrease in appetite as a sign of illness in a dog and a good appetite as a sign of a healthy dog. Dogs with hyperadrenocorticism may begin stealing food, eating garbage, begging continuously, and may exhibit aggressive behavior by attacking other pets for food or protecting their food.

Abdominal enlargement occurs in most dogs affected with hyperadrenocorticism. This potbellied appearance is the result of many factors including enlargement of the liver, weakening of the abdominal muscles, and the redistribution of fat to the abdomen from various other sites of the body. Excessive panting is an associated symptom related to the weakening of the abdominal muscles and the redistribution of fat to the abdomen causing increased pressure on the thoracic area.

Hair loss or alopecia and skin abnormalities are among the most noticeable signs that a dog may have hyperadrenocorticism. Hair loss is usually first noticed at points of wear, such as the elbows and progresses to the dog’s flanks and abdomen. Eventually, the hair loss can become so severe that only the head and distal extremities retain any hair. The skin will become thinner, as a result the dog will bruise easily and wounds will heal more slowly. Muscle weakness or atrophy is also noticed in dogs with hyperadrenocorticism. The dog will be lethargic, have a stiff gait and stumble as a result of the wasting away of muscle tissue.

Treatment
Treatment options depend on the form of hyperadrenocorticism. A surgical procedure to remove adrenal tumors may be an option in cases of ADH. Since surgical removal of the pituitary gland is a specialized procedure, it is not commonly performed in cases of PDH.

Since PDH is the most common form of hyperadrenocorticism observed in dogs, treatment with oral medications is most often the treatment of choice. The medications act either upon the adrenal or pituitary gland to suppress cortisol secretion.

Mitotane or lysodren is the most commonly selected drug to treat hyperadrenocorticism because it can be effective in the treatment of both PDH and ADH. Mitotane is effective for the treatment of ADH and PDH because it acts directly upon the adrenal gland resulting in decreased levels of cortisol. Since mitotane is used to treat both PDH and ADH, many veterinarians do not perform the differential diagnostic tests and just begin treatment once a diagnosis of hyperadrenocorticism is confirmed. Most cases of PDH respond to mitotane treatment at prescribed treatment doses but ADH generally will require a higher mitotane dose for effective treatment. The disadvantage of mitotane treatment is side effects that may include lethargy, anorexia, vomiting, diarrhea, and weakness.

L-deprenyl or anipryl is becoming a popular choice in the treatment of PDH because the side effects are less severe than those of mitotane treatment. Since L-deprenyl acts directly on the pituitary gland to suppress ACTH production, it cannot be used to treat ADH because cortisol is secreted independent of ACTH levels. Often times dogs with advanced PDH do not respond to treatment with L-deprenyl and will have to treated with mitotane.

Throughout treatment, frequent tests will be required to monitor cortisol levels and to evaluate the effectiveness of treatment. Often supportive drug therapy is necessary to treat the side effects. Successful treatment of hyperadrenocorticism relies upon close evaluation during the initial treatment and long term supportive follow-up care. Oxford Laboratories Cortisol Immunoassay Kit can be used for monitoring cortisol levels. Each kit can assay up to 40 samples in duplicate, making cortisol monitoring economical.

The Incidence of Hyperadrenocorticism
Hyperadrenocorticism is generally considered to be a disease of middle age or older dogs. It is usually not found in dogs under 2 years of age and is generally found in dogs over 6 years of age. Dogs with the adrenal-dependent form of hyperadrenocorticism tend to be older than those affected with the pituitary-dependent form of the disease usually over 9 years of age with an average age of approximately 11 years as opposed to 10 years for PDH. Females are at a slightly higher risk for ADH than males, while males and females are at equal risk for PDH.

Poodle breeds, Dachshunds, Terrier breeds, Beagles, and German shepherds are breeds commonly affected with the pituitary-dependent form of the disease although it has been found in numerous breeds. Boston terriers and Boxers also seem to be at increased risk to develop PDH. PDH is usually found in smaller dogs, those generally weighing less than 45 pounds.

Poodle breeds, German shepherds, Dachshunds, Terrier breeds, and Labrador retrievers tend to be the breeds found with adrenal-dependent hyperadrenocorticism. Approximately 50% of the dogs with ADH will be larger than 45 pounds.