What should I know about diagnosis, medication and stages of canine Cushing’s disease?

Original Question: Hi there, what are the stages/timelines for a dog that has been recently diagnosed with Cushing’s disease? Which tests are best to confirm the progression or validity of Cushing’s Low Dex or ACTH? What is the best medicine to use with a Cushing’s diseased dog that has the least amount of side effects? The dog is a rescued female spayed Beagle who came to us late Nov-2017 with 65 pounds of fun and an urinary tract infection. Infection has cleared but evidence of Cushing’s disease showed with her latest urine test. She is now at 55 pounds mainly due to diet, correct portion size and lots of exercise. Thank you. - Anonymous

Apr 24, 2018

Hi there,

Thanks for your question.

Which tests are best to confirm the progression or validity of Cushings Low Dex or ACTH?

First, general blood work and urine testing are always done to rule out other conditions and lead to the suspicion of Cushing’s disease. I assume this has taken place already since your question is now about confirming the diagnosis. The next step is to perform a Low Dose Dexamethasone Suppression test. This is a blood test designed to attempt to confirm the diagnosis. It can be difficult to interpret for some practitioners so if you’re receiving an ambiguous answer, I recommend you consult an internal medicine specialist or request that your veterinarian either contact one or discuss the results with the lab to gain more confidence in the diagnosis. Quite frankly, I have become completely confident and proficient at interpreting the result of this test, but I always like to confirm and discuss the results with a specialist just to review and be completely certain. The lab offers complimentary consultations for veterinarians to call internal medicine specialists about results, so there is no reason I found to not take advantage of this service on behalf of my clients.

Many practitioners will run a test on the urine called a cortisol:creatinine ratio test just to make sure it is consistent with the diagnosis of Cushing’s disease. It is not a very specific test, meaning it doesn’t really lend greater confidence to the confirmation of Cushing’s disease, but it will is very good at eliminating Cushing’s disease as a diagnosis in case a practitioner has mistakenly confirmed Cushing’s disease.

The next test to further confirm Cushing’s disease is to perform an abdominal ultrasound. This is an expensive test where a specialist may come to the clinic or your veterinarian may be able to perform. It images the adrenal glands and measures their size. This will help lend more support for the diagnosis and also helps to determine whether it is one of the two versions of Cushing’s disease, either pituitary-dependent Cushing’s disease or an adrenal tumour. I always like this test performed but due to its cost, some clients decline to have it performed.

What is the best Cushing’s disease medication for dogs that has the least amount of side effects?

There are 2 medications commonly given to treat Cushing’s disease. They are called Trilostane and Mitotane. They each have their advantages and disadvantages. Trilostane is a ‘newer’ drug and Mitotane has been available for much longer. Mitotane is cheaper than Trilostane but has more potential to harm your pet if it is not administered and managed successfully. I would recommend that you discuss each of these options with your veterinarian. The current line of thinking is that the best medication to use is ‘the practitioner’s choice’, meaning whichever drug you use, it should be one that your veterinarian knows extremely well. They will be the person who monitors and then advises you about the progression and treatment of the disease, so if you trust your practitioner, then I would select the one that they are most confident in managing.

The ACTH test is not typically used to confirm or diagnose Cushing’s disease. It is a test that is used to evaluate and manage the treatment and dosage of the medication that is being used.

If you have any doubt about the diagnosis of Cushing’s disease, I would recommend that you consider a consultation with a board-certified internal medicine specialist. This disease can be difficult to diagnose and treat. Once confirmed, it is a lifetime of expensive treatment and management so you want to be certain you have a correct diagnosis before proceeding.