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Canine Cushing's Disease

Cushing's Disease

Canine Cushing's Disease
Frequently Asked Questions

What is Cushing's Syndrome/Disease?

Cushing's syndrome and Cushing's disease in dogs, more accurately known as hyperadrenocorticism is the condition which occurs when the body produces too much hormone, particularly corticosteroids or cortisol.

What Causes Hyperadrenocorticism?

Cushing's syndrome (~15% of all cases of spontaneous hyperadrenocorticism) occurs as the result of a typically benign tumor of the adrenal gland, which causes the gland to secrete excessive amounts of cortisol.

Cushing's disease (~85% of all cases of spontaneous hyperadrenocorticsm) is cased by a typically benign tumor on the pituitary gland, which in turn results in an overproduction of adrenocorticotropic hormone (ACTH), the hormone which stimulates production of corticosteroids by the adrenal gland. Cushing's disease is also commonly referred to as Pituitary-Dependent Hyperadrenocorticism (PDH).

Iatrogenic Cushing's (non-spontaneous) occurs as the result of over administration of corticosteroids such as prednisone.

What are the Symptoms of Cushing's?

Typical physical symptoms include:

  • Increased/excessive drinking (polydipsia or PD)
  • Increased/excessive urination (polyuria or PU)
  • Increased/excessive appetite (polyphagia)
  • enlarged, distended abdomen
  • muscle weakness (most commonly in the back legs)
  • thinning hair (alopecia--usually evenly distributed) and lack of new hair growth
  • thinning skin
  • "skull-like" appearance of head
  • hyperpigmentation of skin
  • calcified skin bumps
  • obesity
  • chronic or frequent infections (most notably pancreatitis, urinary tract infections, strep throat, and staph infections)

Behavioral symptoms include:

  • lethargy/decreased activity
  • increased panting
  • seeking out of cool sleeping surfaces (bathroom tiles, etc.)
  • disturbance of the sleep/wake pattern (increased sleeping during the day, restlessness at night)
  • decreased interaction with owners

How is Cushing's Diagnosed?

As part of a veterinarian's examination, a complete blood count and chemistry panel may be run. Elevated white blood cell counts (especially neutrophils), elevated liver enzymes (particularly alkaline phosphatase), and elevated cholesteral levels in conjunction with clinical symptoms, suggest that Cushing's may be present and indicate a need for further, more specific testing.

To confirm Cushing's, a low-dose dexamethasone test may be done. As part of this test, a blood sample is drawn to measure the baseline (or pre-test) blood cortisol level. Next, an injection of dexamethasone is given. Four to 8 hours later, a second blood sample is drawn to see if the dexamethasone was able to suppress the body cortisol level. In a normal dog, dexamethasone does suppress cortisol levels in the blood. In Cushinoid dogs, cortisol-production suppression does not occur. Thus, a definitive diagnosis is confirmed.

Another commonly used test is the ACTH stimulation test. In this test, ACTH--the adrenal gland-stimulating hormone produced by the pituitary gland--is used instead of dexamethasone.

Another less commonly used, and less well-regarded test is the measurement of the urine cortisol/creatinine ratio.

To confirm the type of Cushing's present, a high-dose dexamethasone suppression test may be run. Most dogs with pituitary tumors will have cortisol suppression on this test. High-dose dexamethasone will have little to no effect on an adrenal tumor.

When the results of a high-dose dexamethasone suppression test are inconclusive (i.e., 49-51% suppression), follow-up x-rays and/or ultrasonography can help reveal the presence or absence of an adrenal gland tumor.

What are the Treatments for Cushing's?

Lysodren (o,p'-DDD or Mitotane) is the most commonly prescribed drug for treating Cushing's Disease (Pituitary Dependent Hyperadrenocorticism). It works by destroying the outer layer of the adrenal glands (adrenal cortices), thus limiting their ability to produce cortisol in response to the ACTH signals of the hyperactive pituitary gland.

Loading Dose. Treatment begins with a "Loading Dose" of Lysodren. The dog is given a large, daily or twice daily dose of Lysodren until a response is seen. The typical response begins with a diminished water intake and/or a diminished appetite, but can also include diarrhea, vomiting, and lethargy. The typical loading period is 6 to 9 days, however, it is crucial that the owner monitor the dog's water and food consumption and observe the dog's behavior as it is possible for the dog to have an extreme response which requires the intervention of a veterinarian. Often, the monitoring vet will prescribe prednisone to keep on hand in case of an extreme reaction. Some vets chose to administer prednisone in conjunction with Lysodren during the loading doses, in order to fend off an adverse reaction.

Maintenance Therapy. Lysodren therapy continues with a weekly or twice-weekly dosage of Lysodren to keep the adrenal cortices killed back. The weekly dosage generally begins at the same level as the daily loading dose, but it is often adjusted as the individual dog's response to the drug indicates.

ACTH stimulation tests may be recommended periodically (every 3 to 6 months, generally) to monitor the progress of Lysodren therapy.

Related Links

Lysodren | Anipryl


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