Wednesday, February 16, 2011

Q & A: Cushing's in dogs...If it looks like a duck and quacks like a...

I saw a 4-year-old, MC Maltese today for a second opinion consult. The dog has severe polyuria and polydispia (PU/PD), and has also developed progressive lethargy, weight gain, extreme panting, and polyphagia over the last few months. The dog also has a marked pot bellied appearance, and has an large liver on abdominal palpation.

Results of my screening lab work is unremarkable except for a high serum alkaline phosphatase (805 U/L; normal < 100 U/L).  The urine specific gravity is dilute at 1.005.

Results of abdominal ultrasound show an enlarged liver with a diffuse increase in echogenicity. The left adrenal gland is mildly plump at 0.6 cm in diameter and 1.45 cm in length. The right adrenal gland was normal in size.

I did a low-dose dexamethasone suppression test with these results:  Pre 8.6 μg/dl;  4-hr Post 0.4 μg/dl; and 8-hr Post 1.4 μg/dl. The owner was told by other veterinarians that these results were not diagnostic for Cushing's syndrome, I guess, because of the 8 hr Post of 1.4 μg/dl.

This dog definitely looks Cushingoid. Clients refused to do a University of Tennessee adrenal panel or a urine creatinine ratio because of finances.  I am very inclined to treat with trilostane.   What do you think?

My Response:

This dog certainly sounds like he has Cushing's syndrome to me, too.  The results of the low-dose dexamethasone suppression test are very suggestive of pituitary-dependent Cushing's disease, with complete suppression at 4 hours and some escape at the 8-hour test period. I understand that the laboratory may have a diagnostic "cut off" value that is slightly higher than 1.4 μg/dl, but this test is very suggestive given the dog's signalment and clinical features.

I do agree with the owner that the University of Tennessee panel is expensive and is probably a waste of money for this dog. Everything so far is pointing to "typical" Cushing's disease so we need to use the time-honored tests for Cushing's first. In many dogs, we have to do more than one of the screening tests (sometimes more than once over to time) to confirm this disease, and you have only done one screening test on one occasion. So which should you do next, the ACTH stimulation test or measure urinary cortisol:creatine ratios (UCCRs)?

I would not bother with an ACTH stimulation test because it has the lowest test sensitivity (only 60-80%). This is another reason not to do the University of Tennessee adrenal panel. In addition, the ACTH that must be injected is expensive.

I would have the owner collect 3 urine samples at home and bring them to your hospital for submission for UCCRs. If money is an issue, you can take a small aliquot (1.0 ml) from each of the 3-day's urine samples the owner collected, and submit the pooled urine for a single UCCR result. This will then give you a 3-day average of urine cortisol secretion. If this is positive, then I'd treat with either trilostane or mitotane.

What if the owner refuses to do more tests? Then I certainly wouldn't start treatment at all. If the owner does not have the money to do a single UCCR, then how can they afford the medication or monitoring costs??  Cushing's is a very serious disease and, unfortunately, we do not have an inexpensive means of treating this disease.


It's time to have a heart to heart talk with the owner about this disease and what they really can afford.

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