What is Cushing’s disease (hyperadrenocorticism)?
Cushing’s disease is one of the most common endocrine disorders that affects middle aged to older dogs (this condition is extremely rare in cats). Cushing’s disease can develop when a dog’s own body overproduces cortisol or when a dog is given corticosteroid medications at high doses and/or over a long period of time. Cushing’s disease is most commonly caused by a small benign growth on the brain that results in over secretion of the hormone cortisol.
Symptoms of Cushing’s disease
Typical clinical signs or Cushing’s disease include
- excessive drinking and urination
- increased appetite
- potbellied appearance
- hair loss and poor coat quality
Once there is reason to suspect Cushing’s disease based on the history, physical examination and initial laboratory testing, it is necessary to do more specific testing to confirm it.
Urine Cortisol/Creatinine Ratio: this is a screening test for Cushing’s disease; a positive test does NOT confirm Cushing’s syndrome but a negative test DOES rule it out. In this test a urine sample is collected to determine the relative amounts of cortisol and creatinine. If there is a high ratio (meaning a relatively high amount of cortisol being excreted) further testing is in order to confirm Cushing’s disease.
ACTH Stimulation Test: A blood sample is collected, then an injection of synthetic adrenocorticotropic hormone is given. A second blood sample is collected 1 hour later to measure and compare the pre and post response to the hormone injection. In dogs with Cushing’s disease, the injection of ACTH causes the adrenal glands to release unusually high amounts of cortisol. If a larger than expected rise in cortisol levels is measured, we may diagnose Cushing’s disease.
Adrenal Steroid Panel: If there is still concerns after the ACTH stimulation test is completed as to whether or not your dog has Cushing’s disease, or something else associated with the adrenal glands an adrenal steroid panel may be run. The panel will test the levels of cortisol, estradiol, androstenedione, 17-hydroxyprogesterone, progesterone and testosterone. These resutls can can give better insight to if you dog has Cushing’s disease or something else such as congenital adrenohyperplasia-like syndrome, Alopecia-X, Atypical Cushing’s Syndrome, or potentially an adrenal tumor.
Treatment and Monitoring
The most common drug used to treat Cushing’s disease is Trilostane (Vetoryl®). Trilostane is an inhibitor of an enzyme called 3-beta-hydroxysteroid dehydrogenase. This enzyme is involved in the production of several steroids, including cortisol. This medication works by blocking an enzyme that is necessary to make cortisol, therefore decreasing its production. As part of its effect, it may also block other hormones normally made by the adrenal gland.
The ACTH stimulation test (as mentioned above) is also crucial in monitoring patients with Cushing’s disease. This test will need to be done every 3-6 months if treatment is stable or more frequently if there is a dose change.
Dogs with Cushing’s disease are more susceptible to infection, can develop hypertension and are more prone to the development of diabetes. However, the biggest risk of Cushings disease is that the medications used to treat it will wipe out too much of the adrenal gland function.
Symptoms to watch for that may indicate that your Cushinoid dog is having complications from their medications
- Decreased appetite
- Excssive drinking
If your Cushinoid dog is showing any of these symptoms, or seems off at any time an examination, general blood work and ACTH stimulation test is recommended. This will make sure everything is alright with your dog and let us know if a dose change is needed.
As long as the medication is given as prescribed and blood work is run regularly as recommended by the veterinarian, dogs with Cushing’s disease can live normal lives with out complications.