Cushing's Disease or Hyperadrenocorticism
The adrenal glands sit next to the kidneys in a dog or cat's abdomen. They are made up of a cortex, or outer layer, and medulla, or inner layer. The cortex is responsible for secreting sex steroids (estrogen and testosterone) and cortisol (natural adrenaline), and the medulla is responsible for secreting mineralocorticoid hormones that help regulate salt and water balance in the body. The pituitary gland in the brain is responsible for helping to regulate how much hormones the adrenal glands produce (essentially is the on/off switch).
With Cushing's disease, there is an overproduction of cortisol secretion within the body. This can be a primary problem with the adrenal glands (adrenal tumors), caused by medications (steroids) given for other conditions, and most commonly from an abnormal pituitary gland within the brain (usually due to a microscopic benign tumor). Benign pituitary tumors account for around 85% of Cushing's disease in dogs. Cats rarely get Cushing's disease, and when they do they usually have diabetes as well.
With Cushing's disease, there is an overproduction of cortisol secretion within the body. This can be a primary problem with the adrenal glands (adrenal tumors), caused by medications (steroids) given for other conditions, and most commonly from an abnormal pituitary gland within the brain (usually due to a microscopic benign tumor). Benign pituitary tumors account for around 85% of Cushing's disease in dogs. Cats rarely get Cushing's disease, and when they do they usually have diabetes as well.
Symptoms
Dogs with Cushing's disease are typically middle aged to older (over 7 years of age typically) and no breed or sex is predisposed. The following are common symptoms we see in cushingoid dogs:
- Thinning hair or hair loss, or hair that does not grow back when shaved
- Increased water consumption
- Increased urination
- Increased appetite
- Pot-bellied appearance to abdomen
- Thin skin which is easily torn or damaged
Diagnosis
In any pet where Cushing's may be a concern the first tests we will recommend are a blood panel and a urinalysis. The following findings are very common in Cushing's pets:
LDDS Testing
If bloodwork is suggestive of Cushing's, a blood test needs to be performed to confirm this diagnosis. This is called a low dose dexamethasone suppression test, or LDDS test. With this test, we take a blood sample and then give an intravenous injection of dexamethasone, a short acting steroid. In normal dogs, this would cause the body's cortisol level to drop dramatically, because the pituitary gland would recognize that there was too much steroid already within the body and would signal the adrenal glands to stop producing their own steroid. Then we take blood samples at 4 hours and 8 hours after administering the steroid. All 3 blood samples are sent to a nearby lab to test the cortisol amount in each blood sample. We then get the following results:
There are some cases where the LDDS test results are inconclusive. In these cases, we will need to perform additional testing to see if your pet has atypical Cushing's. A more comprehensive hormone panel can be sent to a lab to achieve a diagnosis.
- Increased liver enzymes - especially one called ALP, which becomes highly elevated in response to prolonged high levels of steroids within the body (either naturally occurring or from pills or injections of steroids)
- Increased cholesterol
- Dilute urine
LDDS Testing
If bloodwork is suggestive of Cushing's, a blood test needs to be performed to confirm this diagnosis. This is called a low dose dexamethasone suppression test, or LDDS test. With this test, we take a blood sample and then give an intravenous injection of dexamethasone, a short acting steroid. In normal dogs, this would cause the body's cortisol level to drop dramatically, because the pituitary gland would recognize that there was too much steroid already within the body and would signal the adrenal glands to stop producing their own steroid. Then we take blood samples at 4 hours and 8 hours after administering the steroid. All 3 blood samples are sent to a nearby lab to test the cortisol amount in each blood sample. We then get the following results:
- Normal dogs will have resting cortisol levels within the normal range, and their 4 and 8 hour cortisol levels will be lower than their resting levels because the production of natural steroids has been stopped
- Dogs with Cushing's disease will have elevated resting cortisol levels and will not show a decreased level of cortisol in the following blood samples. This test can also be useful in deciding if there is an adrenal tumor or a pituitary abnormality because there will be different results on this test for each type of Cushing's disease.
There are some cases where the LDDS test results are inconclusive. In these cases, we will need to perform additional testing to see if your pet has atypical Cushing's. A more comprehensive hormone panel can be sent to a lab to achieve a diagnosis.
Treatment
Treating Cushing's disease depends on what type your pet has. With adrenal tumors, surgical removal is usually the treatment of choice, but surgery itself can be very risky with not all pets surviving surgery. Pituitary tumors are not usually removed and medical treatment is used instead.
Lysodren and Vetoryl are the two different medications we use here to treat Cushing's disease in dogs. This medication will kill some of the cells in the outer cortex of the adrenal gland that produces cortisol. At appropriate doses, it will kill just enough of the cells to allow the levels within the body to return to normal. Once we start a pet on this medication, it needs to be continued for the rest of the animal's life in order for the Cushing's disease to be well controlled. In addition, monitoring is required to ensure that the medication is working and that your pet is tolerating the medication well. If there is too much medication being given, hypoadrenocorticism (or Addison's disease) could develop.
About 30 days after starting therapy, we will need to see your pet back for a follow-up evaluation and to perform an ACTH stimulation test. This test checks to make sure the cortisol levels in the blood are normal and that the medication is working. In addition, we will recheck some bloodwork to make sure your pet is not having any adverse reactions to the medication. After initial treatment and monitoring, we usually will recheck bloodwork on a yearly basis unless side effects occur.
Side effects of Lysodren and Vetoryl (or symptoms that could indicate a problem) include:
Lysodren and Vetoryl are the two different medications we use here to treat Cushing's disease in dogs. This medication will kill some of the cells in the outer cortex of the adrenal gland that produces cortisol. At appropriate doses, it will kill just enough of the cells to allow the levels within the body to return to normal. Once we start a pet on this medication, it needs to be continued for the rest of the animal's life in order for the Cushing's disease to be well controlled. In addition, monitoring is required to ensure that the medication is working and that your pet is tolerating the medication well. If there is too much medication being given, hypoadrenocorticism (or Addison's disease) could develop.
About 30 days after starting therapy, we will need to see your pet back for a follow-up evaluation and to perform an ACTH stimulation test. This test checks to make sure the cortisol levels in the blood are normal and that the medication is working. In addition, we will recheck some bloodwork to make sure your pet is not having any adverse reactions to the medication. After initial treatment and monitoring, we usually will recheck bloodwork on a yearly basis unless side effects occur.
Side effects of Lysodren and Vetoryl (or symptoms that could indicate a problem) include:
- Lethargy or depression
- Weakness
- Vomiting or diarrhea
- Inappetance
Prognosis and Life Span
Dogs with Cushing's disease usually live about 2-4 years from the time of diagnosis, with or without treatment. Medical therapy is not a cure but a way to manage the disease. It may not increase their life span much, but it does significantly improve their quality of life, and dogs are much happier when on the medication.