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490 Hyperadrenocorticism, Occult

Client Education SUGGESTED READING AUTHOR: Sara Galac, DVM, PhD
Clients must be aware of the risks of trilostane Galac S, et al: ACTH-independent hyperadrenocorti- EDITOR: Ellen N. Behrend, VMD, PhD, DACVIM
VetBooks.ir a dog: a case report. Vet J 177:141, 2008.
therapy (p. 485).
cism due to food-dependent hypercortisolemia in

Hyperadrenocorticism, Occult

BASIC INFORMATION ACTH stimulation test with measurement of only laboratory abnormalities (e.g., elevated
sex hormones before and after ACTH should alkaline phosphatase [ALP]).
Definition be considered.
A syndrome in which a dog appears to have Acute General Treatment
hyperadrenocorticism (HAC) based on history, Differential Diagnosis Acute treatment is not needed.
physical exam, and clinicopathologic findings, • Classic HAC
but results of the low-dose dexamethasone sup- • Adrenocortical neoplasia with secretion of Chronic Treatment
pression test (LDDST) and standard ACTH a cortisol intermediate or progestin • Treatment of occult HAC with lignans
stimulation test fall into currently accepted • Food-induced HAC (HMR lignan 10-40 mg/DOG q 24h) and
reference ranges. • Any of the differential diagnoses for the melatonin 3-6 mg PO q 12h has been
clinical signs present recommended, but efficacy is unknown.
Synonym • Treatment can be undertaken as for pituitary-
Atypical hyperadrenocorticism Initial Database dependent HAC (p. 485)
Perform initial database as for classic HAC; ○ For occult HAC, whether dosages of
Epidemiology similar findings expected mitotane or trilostane should be changed,
SPECIES, AGE, SEX as well as their efficacy, are unknown.
Middle-aged to older dogs Advanced or Confirmatory Testing ○ In theory, trilostane may be less effective
• Testing for classic HAC must be done before than mitotane for treating occult HAC
Clinical Presentation considering occult HAC (pp. 485, 1300, due to its mechanism of action. However,
HISTORY, CHIEF COMPLAINT and 1360). relative efficacy for occult HAC has never
History identical to that for classic HAC (i.e., • If clinical signs are mild, wait and retest for been evaluated, and either drug can be
HAC due to cortisol excess [p. 485]) classic HAC later if progression is noted. tried.
• If clinical signs are moderate to severe,
PHYSICAL EXAM FINDINGS perform an abdominal ultrasound. Possible Complications
Exam findings are identical to those for classic ○ If an adrenal tumor is present, it may be • Complications of lignans and melatonin
HAC. the cause of the clinical signs (p. 35). therapy are unknown but appear mild (e.g.,
○ If the adrenal glands are normal, HAC is lethargy).
Etiology and Pathophysiology unlikely. • Hyperadrenocorticism (p. 485)
• The cause of occult HAC is unknown. ○ Bilateral adrenomegaly is supportive of,
Possibilities are: but is not specific for, HAC. Recommended Monitoring
○ Aberrant adrenocortical production and • If clinical signs are moderate to severe and • If using lignans and melatonin, judge
secretion of sex hormones abdominal ultrasound showed bilateral response subjectively based on clinical signs.
○ Cutoff values for the endocrine tests adrenomegaly, consider • If using trilostane or mitotane, monitor as for
(LDDST, ACTH stimulation test) may ○ Pituitary imaging to identify a tumor pituitary-dependent HAC. The best hormone
be inappropriate. causing early HAC to monitor is unknown.
○ Variable cortisol sensitivity may exist in ○ Food-induced HAC (p. 489): urine
dogs; those with high sensitivity may cortisol/creatinine ratio before and after PROGNOSIS & OUTCOME
show clinical signs of HAC at cortisol meal feeding, octreotide suppression
concentrations considered normal. • If clinical signs are moderate to severe and all Survival data unknown but likely similar to or
○ Some dogs that appear to have occult HAC above are normal, perform an ACTH stimula- better than for dogs with pituitary-dependent
may have food-dependent HAC (p. 489). tion test (p. 1300) but instead of measuring only HAC
• If occult HAC is related to sex hormone cortisol, sex hormone concentrations should be
excess, progestins would be involved because measured (https://vetmed.tennessee.edu/vmc/ PEARLS & CONSIDERATIONS
they bind the glucocorticoid receptor. dls/Endocrinology/Pages/default.aspx)
• Although abnormalities such as sudden ○ Only the post-ACTH sex hormone concen- Comments
acquired retinal degeneration syndrome trations should be used to make a diagnosis • Occult HAC should be considered only if
(SARDS [p. 883]) and hyperphosphatasemia of occult HAC. Pre-ACTH concentrations clinical signs suggest HAC but results of an
in Scottish terriers have been linked to occult of sex hormones are not helpful. ACTH stimulation test with measurement
HAC, causative evidence is lacking. ○ Test specificity is 70%; dogs with non- of cortisol and an LDDST are normal.
adrenal illness can have increased serum • Abnormal laboratory results alone (e.g.,
DIAGNOSIS sex hormone concentrations. elevated ALP) are not sufficient reason to treat.
Diagnostic Overview TREATMENT Technician Tips
Occult HAC should be suspected when history When performing an ACTH stimulation test
and clinical signs of HAC are present but both Treatment Overview with measurement of a sex hormone panel,
the LDDST and standard ACTH stimulation Treatment goal is resolution of clinical signs, 2 mL of serum is required in the pre- and
test are normal. If occult HAC is suspected, an and therapy should not be undertaken to resolve post-ACTH samples.
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