Hyperadrenocorticism Flashcards
what are the causes of hyperadrenocorticism
Spontaneous:Pituitary dependent: 85%
Pituitary tumour: >90%
Adrenal dependent
Adrenal tumour: >90%
Iatrogenic
what is the pathophysiology of pituitary dependent HAC
Functional adrenocorticotropic hormone (ACTH) secreting pituitary tumour in approx. 85% of dogs
- Excessive secretion of ACTH causes bilateral adrenocortical hyperplasia and excess cortisol secretion from the adrenal cortex
- Because normal feedback inhibitor of ACTH secretion by cortisol is missing excessive ACTH secretion persists despite increased adrenocortical secretion of cortisol
- Episodic secretion of ACTH and cortisol is common and results in fluctuating plasma concentrations that at times may be in the reference range
how is HAC diagnosed
- clinical signs
- screening tests
- specific tests: confirming, identifying the cause
what is the signalment of HAC (5)
- Typically in dogs 6 years and older (median 10 years) but can be in younger dogs
- No sex predisposition (but ADH may be more common in female dogs)
- Poodle, Dachsunds, Terriers, GSD, Boxers, Boston terriers
- PDH more common in small dogs
- ADH more common in larger dogs
what are the most common clinical signs of HAC (7)
- Polyuria, polydipsia, polyphagia
- Respiratory signs: panting
- Abdominal enlargement
- Endocrine alopecia
- Mild muscle weakness
- Lethargy
- obesity
what are the dermatological changes seen in HAC (3)
- Non-pruritic truncal alopecia
- Thin skin
- Failure to regrow shaved hair
what are uncommon clinical signs seen in HAC (7)
- Suppression of pituitary function –> persistent anestrus, testicular atrophy, secondary hypothyroidism
- Laxity of ligaments may lead to lameness
- Hypercoagulability may result in formation of spontaneous thrombi, typically involving pulmonary vessels and resulting in acute resp distress
- Cortisol insulin resistance
- Persistent hypertension
- Neurological signs: obtunded, dopey, fall asleep, apparently blind
- Myotonia: relaxation of muscle is impaired
what is iatrogenic HAC
too long of steroid course
make sure you search in history if there has been steroid use
what can be seen on serum bioch with HAC (6)
- increased ALP: steroid induced production
- increased cholesterol
- increased glucose (only slightly)
- increased ALT, GGT, AST (won’t increase to the extent of ALP)
- increased bile salts (steroid hepatopathy)
- decreased urea and creatinine (PUPD)
what can be seen on hematology in HAC
stress leukogram
- neutrophilia
- lymphopenia
- eosinophilia
- monocyotosis
- erthrocytosis
what can be seen in urinalysis HAC (4)
- low SG (< 1.020)
- proteinuria
- urinary tract infection
- glucosuria
what radiographic changes can be seen in HAC (2)
- many changes largely non-specific
- prognostic important: adrenal masses, thoracic metastases, intercurrent disease
what is the principle of the ACTH stimulation tests
ACTH stimulates adrenal cortex to maxillary secrete cortisol
how is an ACTH stimulation test done (3)
- take blood sample for basal cortisol
- administer 0.2 mg ACTH IV or IM
- take second blood sample 0.5-2 hours
what is the sensitivity with ACTH stimulation
only 50% of dogs with AD-HAC will be indentified
only 85% of dogs with PD-HAC will be identified
how do you interpret the results of ACTH stimulation test
Dogs with hyperadrenocorticism have an increased post-ACTH admin cortisol increase
The absence of a response is suggestive of adrenocortical neoplasia or iatrogenic hyperadrenocorticism
what is the priniciple of low dose dexamethasone suppression test
Dexamethasone suppresses ACTH secretion
Rapid recovery, or failure to suppress, in HAC
how is a low dose dexamethasone test done (3)
- take blood sample for basal cortisol
- administer 0.015 mg/kg dexamethasone IV
- take blood sample 3 and 8 hours later
how do you interpret the results of a low dose dexamethasone suppression test
in an AD/PD-HAC dog dexamethasone will not suppress cortisol at all
in a PD-HAC dog it will be able to suppress it for some time but then cortisol levels will increase again
normal dogs will suppress cortisol
what other tests can diagnose HAC (2)
- 17 hydroxyprogesterone: cortisol precursor
- urine corticoid:creatinine ratio approximation of 24 hour total urine cortisol
what is an ACTH assay used for
to identify the cause of HAC
how is an ACTH assay done
ACTH decays very quickly at room temp
send frozen EDTA plasma to a specialist lab
how is an ACTH assay interpreted
PD-HAC results in increased ACTH concentrations
AD-HAC results in suppression of ACTH secretion
is HAC common in cats
no its rare
