Diagnosis of hyperadrenocorticism should include an evaluation of the animal's history and clinical signs, as well as the results of blood chemistry and screening tests.
A "stress leukogram" secondary to excess cortisol is a common finding on the CBC and includes a neutrophilia, monocytosis, lymphopenia and eosinopenia. An increase in serum alkaline phosphatase (SAP) secondary to corticosteroid induction is a common finding on a biochemical panel. Hypercholesterolemia, increased alanine aminotransferase (ALT) and mild hyperglycemia may also be noted in dogs. In cats, hyperglycemia is much more common since there is often concurrent diabetes mellitus. Urine is usually dilute and glucosuria is often present in cats secondary to diabetes mellitus. Urinary tract infections are common, however clinical signs and inflammatory changes in the urine may be absent because excess cortisol suppresses inflammation.
Screening tests for hyperadrenocorticism should only be performed in animals with appropriate history and clinical signs. The currently available screening tests include: urine cortisol:creatinine ratio, low-dose dexamethasone suppression test and ACTH stimulation test.
Low-Dose Dexamethasone Suppression Protocol
For cases of suspected Cushing's syndrome
 | | View/print the diagnostic protocol.  A low-dose dexamethasone suppression test may provide a definitive diagnosis. It measures and compares the levels of cortisol in an animal's bloodstream before and after it receives an injection of dexamethasone. Post-injection, healthy animals show suppressed cortisol levels. |
ACTH Stimulation Test
Diagnostic Protocol for Cases of Suspected Cushing's Syndrome or Addison's Disease
 | | View/print the diagnostic protocol. The ACTH stimulation test may also provide a definitive diagnosis. It measures and compares the levels of cortisol in an animal's bloodstream before and after the animal receives an injection of ACTH. Post-injection, an animal with Cushing's disease will have greatly elevated cortisol levels. |
High-Dose Dexamethasone Suppression Protocol
For Determination of Pituitary-Dependent vs. Adrenal Tumor Cushing's Syndrome
 | | View/print the diagnostic protocol. Once a diagnosis of hyperadrenocorticism is made, testing should be performed to differentiate pituitary dependent hyperadrenocorticism (PDH) from adrenocortical tumor hyperadrenocorticism (ATH). Approximately 80% of dogs with hyperadrenocorticism have PDH whereas only 20% have ATH. Of dogs with ATH, about 50% of tumors are malignant and 50% are benign. A high-dose dexamethasone suppression test (HDDS) may help to differentiate PDH from ATH. Alternatively, an abdominal ultrasound or measurement of endogenous ACTH may be useful. |
The decision to treat should be based on laboratory testing and the presence of clinical signs such as polyuria/polydipsia, abdominal enlargement, alopecia, decreased exercise tolerance, calcinosis cutis, hyperpigmentation, panting, lethargy and obesity. Additionally, the treatment protocol depends on the type of disease.
- Pituitary dependent hyperadrenocorticism is treated medically. Medications that are currently used include o,p’-DDD (mitotane [Lysodren®]) which is adrenocorticolytic, and trilostane (Vetoryl®) which blocks the excessive production of cortisol by reversibly inhibiting the action of the enzyme 3-β hydroxysteroid dehydrogenase.
- Surgery is the treatment of choice for ATH. Though technically difficult, the surgery is highly effective in curing Cushing’s if the tumor hasn’t invaded surrounding tissue or metastasized to other organs.
Monitoring
Dogs being medically treated for Cushing’s syndrome need to be monitored closely. Overtreatment can result in a deficiency of cortisol and/or mineralocorticoids which can lead to clinical signs of hypoadrenocorticism or Addison’s disease. If undetected, this can be fatal.
Mitotane (Lysodren®) Dosing and Monitoring Protocol
