Internal Medicine Clinical Update: Hyperadrenocorticism
Hyperadrenocorticism (HAC) is a common endocrinopathy. More often or affecting middle-aged to older dogs. In the last decade there has been extensive research into the diagnosis, treatment and clinical outcomes of HAC. This clinical update will be the first of a two part series designed to cover the diagnosis of canine HAC and discuss current trends in the treatment of HAC.
Recently, the American College of Veterinary Internal Medicine (ACVIM) released a consensus statement that summarizes the most up-to-date information on the diagnosis of spontaneous canine HAC. The statement covers indications for screening tests and tests used to differentiate between pituitary dependent HAC (PDH) and adrenal dependent HAC (ADH).
The presentation of canine HAC can be quite varied, and dogs may display subtle clinical signs or a constellation including some or all of polyuria, polydipsia, alopecia or a pendulus abdomen. The ACVIM panel noted that the more abnormalities consistent with HAC identified on physical examination, the stronger the indication to proceed with diagnostic testing screening. Although failure to identify common clinical manifestations and laboratory abnormalities does not rule out HAC, a thorough review of the history, physical exam findings and routine laboratory tests should be performed prior to proceeding with further testing.
Tests used in the screening and diagnosis of HAC look for increased cortisol production or sensitivity of the hypothalamic-pituitary-adrenal axis to negative glucocorticoid feedback. No test for HAC has 100% diagnostic accuracy and any screening test can be negative in a patient with HAC If more then 1 screening test for HAC is negative then the potential for other diseases must be considered.
Consensus conclusions regarding screening tests are as follows:
- The low dose dexamethasone suppression test (LDDST) is the screening test of choice
- Criteria for the diagnosis of PDH by LDDST is
- a 4 hr post- dexamethasone plasma cortisol concentration below lab cut-off or 50% of baseline cortisol concentration OR an 8 hr cortisol concentration <50% of baseline cortisol concentration but greater then the lab cut-off
- A normal urine cortisol: creatinine concentration is used to rule out HAC and a positive test is not diagnostic for HAC
- A random serum cortisol concentration has no diagnostic value at this time
- An ACTH stimulation test is inferior to a LDDST due to low sensitivity
- The ACTH stimulation test is the gold standard for diagnosis of iatrogenic HAC
The determination and differentiation of PDH from an adrenal tumor has implications for both treatment and prognosis.
Consensus conclusions regarding differentiating tests
- Dexamethasone suppression (low and high) can help distinguish between the two; if suppression occurs then likely PDH
- Lack of suppression can occur with both PDH and AT
- If there is no suppression on a LDDST then an abdominal ultrasound is recommended as the second diagnostic test
- Adrenal width can vary with breed, body size, improper alignment and hyperplasia
- Adrenal width > 4 cm is highly correlated with malignancy
If you have any questions regarding the diagnosis of hyperadrenocorticism, the consensus statements or any other cases please do not hesitate to contact Dr. Michael Goldstein at 416-784-4444.
Posted by: Michael Goldstein, DVM, Diplomate ACVIM
Categorised as: Blog & Articles
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