It may not be Cushing's....is the Alk Phosphate elevated too?
Here's a note from an endocrine vet:
"However, bilateral adrenal enlargement was noted, and the radiologist recommended a workup for Cushing's disease"
Hyperadrenocorticism (Cushing's disease) is a clinical diagnosis and is based primarily on the finding of compatible signs (e.g., polydipsia, polyphagia hepatomegaly, hair loss, pot-belly). In a dog suspected of suffering from Cushing's syndrome, we confirm the diagnosis by using one or more of the adrenal function tests (e.g, ACTH stimulation or low-dose dexamethasone suppression tests) (5-7).
One should never make a diagnosis of hyperadrenocorticism based on the finding of large adrenal gland size alone. Remember that the stress of any nonadrenal illness commonly leads to an overactive hypothalmic-pituitary-adrenal axis. Therefore, any dog with chronic stress or illness can develop bilateral adrenocortical hyperplasia as a physiological response. I know that some radiologists like to diagnose Cushing's disease based on adrenal gland size, but this just cannot be done using this criteria alone (5,6). Dogs with Cushing's disease certainly tend to have larger adrenal glands, but large adrenal glands alone are not diagnostic for this disease.
Cushings can also be treated with things like ketoconazole, which is noted from the link above. Has your dog been on prednisone at all? Are there any skin issues?
The Cushing's test is expensive - it's similar to the one for Addison's. I paid $400 (U.S.) for Jazz's addision test (she had to have two
Some dogs do better without treatment from what I read, but if there are symptoms, I think I might consult a holistic type vet, and see if there are any herbal preparations that block cortisol.