Page 989 - Cote clinical veterinary advisor dogs and cats 4th

486 Hyperadrenocorticism

(LDDST) and/or urine cortisol/creatinine • UC/CR chance), results are not diagnostic. If
ratio (UC/CR) ○ Protocol (p. 1391): owner should collect eACTH measured again, almost 100%
VetBooks.ir dog that has a nonadrenal illness, it is best ○ An elevated UC/CR may be a sensitive There is no way to predict when eACTH
chance of obtaining differentiation.
sample at home when pet not stressed.
• If clinical signs of HAC are present in a
to postpone testing for HAC until the
marker of HAC, found in 90%-100%
concentration will be in the gray zone.
nonadrenal illness has resolved, if possible.
○ Never use for screening. Bilateral adreno-
studies have found a sensitivity of only
• Sensitivity and specificity of the tests are of affected dogs in most studies. Some • Abdominal ultrasound
unknown in cats. 75%. megaly can be due to chronic nonadrenal
• ACTH stimulation test ○ False-positive results common; only illness, and ATs do not always cause
○ Only test that can diagnose iatrogenic 25%-30% of dogs with an elevated UC/ HAC.
HAC; diagnosis based on history of CR have HAC. ○ Maximal dorsoventral dimension of
glucocorticoid exposure by any route, ○ Elevated ratio consistent with a diagnosis adrenal gland in a sagittal plane most
consistent clinical signs, and post-ACTH of HAC, but because the chance of a informative parameter
cortisol concentration below reference false-positive result is great, an ACTH ○ Bilateral adrenomegaly present in > 90%
range. stimulation test or LDDST must be done of dogs with PDH
○ Protocol (p. 1300): cosyntropin is the to confirm the diagnosis. ○ Defines location, size, and organ involve-
recommended form of ACTH to use; ○ A protocol with reportedly high sensi- ment of AT more precisely than radiog-
if using compounded ACTH, collect tivity and specificity exists in Europe; a raphy. Moderate asymmetry, contralateral
samples before and at 1 and 2 hours after minimum of two morning urine samples adrenocortical atrophy, and destruction of
ACTH administration so peak response are collected, dexamethasone is then normal tissue architecture are consistent
not missed administered (3 doses PO over 24 hours) with cortisol-secreting AT.
○ A response greater than normal is con- for differentiating purposes, and another ○ Indicators of malignancy are invasion of
sistent with a diagnosis of spontaneous urine sample is collected. Unfortunately, adjacent structures, presence of lesions
HAC; cortisol concentrations below the cortisol assay used is proprietary and suggestive of metastasis, and AT diameter
normal, often too low to be measured, are not commercially available. Because the > 2 cm.
consistent with a diagnosis of iatrogenic accuracy of the protocol using cortisol • Pituitary imaging can be done if there is
HAC. assays commercially available in the suspicion of macroadenoma.
○ Overall sensitivity of the test is approxi- United States has not been established, • Abdominal CT: preoperatively if adrenalec-
mately 80%; for PDH, sensitivity is the method is not recommended for use tomy is to be performed for ATH
approximately 85%-90% and, for ATH, in the United States and Canada.
sensitivity is approximately 60% After a diagnosis of HAC is made, a differentia- TREATMENT
○ Compared with LDDST, may have less tion test should be performed (i.e., high-dose
chance of a false-positive result in a dog dexamethasone suppression test, endogenous Treatment Overview
with nonadrenal illness ACTH concentration, or abdominal ultrasound) Treatment goal is resolution of clinical signs.
○ Can never differentiate between PDH and to determine if PDH or ATH present. For PDH, hypophysectomy ideal but of very
an ATH • Differentiation provides information crucial limited availability. Medical therapy (trilostane
• LDDST to therapeutic decisions and an accurate or mitotane) is usually used in dogs with PDH,
○ Protocol (p. 1360): if using dexamethasone prognosis. but response is inconsistent in cats (trilostane
sodium phosphate, dose on concentration • High-dose dexamethasone suppression test best for cats). If ATH, adrenalectomy is
of parent compound, not the salt. (HDDST) preferred in dogs and cats.
○ May be the preferred screening test for ○ Protocol: same as for LDDST, but
diagnosis of spontaneous HAC dexamethasone dose higher (p. 1353) Acute General Treatment
○ Sensitivity is approximately 95% in dogs. ○ If the LDDST provided a diagnosis of HAC Acute therapy unnecessary
○ Relatively high chance of false-positive but did not differentiate between PDH and
result exists, up to 50%, if nonadrenal ATH, HDDST is unlikely to differentiate. Chronic Treatment
illness present ○ Two responses are consistent with • Not all dogs with positive test results for
○ If test positive for HAC, may also serve PDH; if there is suppression to less than HAC need to be treated. The decision should
to differentiate PDH from ATH cutoff value at 4 and/or 8 hours after be made on a case-by-case basis. Consider-
If the 8-hour sample is > the cutoff dexamethasone or the 4- and/or 8-hour ation should be given to the dog’s health,
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value, result is consistent with HAC. post-dexamethasone samples are < 50% quality of life, owner needs and limitations,
If in addition, the 4-hour post- of baseline, PDH is present and severity of clinical signs.
dexamethasone cortisol concentration ○ If baseline values are close to cutoff value • For medical therapy, mitotane and trilostane
is < the cutoff or the 4- and/or 8-hour or suppression just at 50%, results are are preferred; L-deprenyl and ketoconazole
post-dexamethasone concentrations are suspect, and PDH should be confirmed are of low efficacy.
< 50% of baseline, results consistent by other means. • For patients on medical therapy, owners
with PDH ○ HDDST can never confirm ATH; if should have prednisone 0.2 mg/kg available
If criteria for PDH not met, chances criteria for PDH diagnosis are not met, to administer at home if needed.
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approximately 50/50 for PDH versus there is a 50 : 50 chance the patient has • Trilostane (Vetoryl)
ATH PDH or ATH. ○ Inhibits synthesis and secretion of adreno-
○ If the baseline cortisol concentration is • Endogenous ACTH (eACTH) concentration cortical steroids, particularly cortisol and,
close to the cutoff value or suppression is ○ With PDH, eACTH concentration is to a lesser extent, aldosterone.
just at 50%, PDH should be confirmed inappropriately high. With ATH, eACTH ○ Brand name product should be used due
by other means. is low or undetectable. to variability in compounding.
○ If cortisol concentration 4 hours after ○ Protocol (p. 1299): proper sample han- ○ Competitive inhibitor of the enzyme
dexamethasone is above the cutoff and dling is crucial. 3-beta-hydroxysteroid dehydrogenase
the 8-hour sample is below, HAC is ○ Can confirm presence of ATH ○ Goal is control of cortisol secretion.
possible, and an ACTH stimulation test ○ Gray zone exists in results. If eACTH ○ Administer with food to enhance
is recommended. is in the gray zone (approximately 15% absorption.

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