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53 Cards in this Set
- Front
- Back
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What is the hypothalamic pituitary adrenal axis that regulates cortisol release?
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Hypothalamus releases corticotropin releasing hormone (CRH)---> anterior pituitary releasing ACTH---> adrenal gland releases cortisol
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What regions of the adrenal gland release glucocorticoids?
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Zona fasciculata and zona reticularis of the adrenal cortex
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What are 4 functions of cortisol?
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1) stimulates gluconeogenesis
2) Antagonizes insulin 3) Increases lipolysis 4) Immunosuppressive |
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What part of the adrenal gland releases aldosterone?
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Mineralocorticoids are released by the zona glomerulosa in the adrenal cortex
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What regulates aldosterone release?
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Serum K+
Renin-angiotensin system |
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What is the function of aldosterone?
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Promotes reabsorption of sodium and excretion of potassium in the distal tubule
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How do you measure plasma cortisol? Is baseline cortisol useful diagnostically?
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Immunoassay
Baseline cortisol not useful diagnostically |
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Does prednisone and dexamethasone interfere with measuring plasma cortisol?
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Prednisone cross-reacts
Dexamethasone doesn't |
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What do you want to collect blood into if running plasma cortisol assays?
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Heparin OR
EDTA |
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Can you freeze a sample that you are going to measure cortisol levels on?
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Yes, freezing/thawing doesn't change cortisol
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What is the ACTH stimulation test used to diagnose?
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May be used for diagnosis of hyperadrenocorticism, but is THE test for hypoadrenocorticism
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What is the test of choice to diagnose hypoadrenocorticism?
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ACTH stimulation test
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How do you perform an ACTH stimulation test?
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Draw pre-sample, inject ACTH, take post-sample
-Normal will increase 2-3 X -Dogs with hyperadrenocorticism will increase to > 20 ug /dl |
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The dose and time of ACTH injection depends on _____ and ______.
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Species and form of ACTH
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What is the sensitivity of the ACTH stimulation test for naturally-occurring hyperadrenocorticism in dogs?
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80-85% in dogs, less sensitive for adrenal tumors
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Is the ACTH stimulation test or low dose dexamethasone suppression test more specific for hyperadrenocorticism?
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ACTH stimulation
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ACTH stimulation test isn't a great diagnostic for hyperadrenocorticism in _______.
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Horses
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ACTH stimulation test is the test of choice for what 3 things?
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1) Hypoadrenocorticism
2) Iatrogenic hyperadrenocorticism 3) Monitoring op'-DDD therapy for hyperadrenocortisim |
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What is low dose dexamethasone suppression used for?
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Screening for hyperadrenocorticism in dogs, cats and horses
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How is a low dose dexamethasone suppression test performed?
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Baseline sample for cortisol, give dexamethasone IV
-Take samples at 4 & 8 hours; 18-20 hours for horses |
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What is the results of a normal animal to the low dose dex test?
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Should suppress cortisol to < 1.0-1.5 ug/dl by 8 hours
-Some pituitary dependent hyperadrenocorticism dogs will suppress at 4 but not 8 hrs |
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Does ACTH stimulation or low dose dex suppression have a higher sensitivity for hyperadrenocorticism? Specificity?
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low dose dex (90-95%)-sensitivity
ACTH= higher specificity |
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What is the urine cortisol:creatinine ratio based on?
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Based on concept that cortisol concentration in a random urine sample will reflect the cortisol concentration at time of urination
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What is the urine cortisol:creatinine ratio used for? Why?
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Stress can also cause an increase in the ratio so it is very sensitive but not specific, so if normal it rules out hyperadrenocorticism, but a high test result is not diagnostic
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What is the high dose dexamethosone suppression test used for?
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To distinguish pituitary dependent hyperadrenocorticism from adrenal dependent hyperadrenocorticism
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How is the high dose dexamethasone suppression test performed?
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Baseline cortisol sample, then 0.1 mg/kg (dogs) dex given and post sample at 8 hours
-ADH dogs don't suppress to <50% baseline -About 20% of PDH dogs also don't suppress |
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What does it mean if a high dose dexamethasone suppression test causes suppression?
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Means the hyperadrenocorticism is pituitary dependent
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What does it mean if a high dose dexamethasone suppression test doesn't cause suppression?
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Adrenal dependent hyperadrenocorticism or pituitary dependent
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What is the high dose dex test based on?
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Idea that high dose of dex will suppress ACTH production by an adenoma in the pituitary gland, but it won't suppress an adrenal tumor that acts autonomously
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What is the endogenous plasma ACTH assay used for?
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Reliable for distinguishing ADH from PDH
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The endogenous plasma ACTH assay is not good for screening in ______.
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Dogs-can't screen for hyperadrenocorticism just distinguishing cause
May be useful for screening in horses... |
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How do you know if a dog has ADH vs PDH using the endogenous plasma ACTH assay?
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ACTH increase in PDH dogs
ACTH decrease in ADH dogs |
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What is the biggest problem with the endogenous plasma ACTH assay? How can you prevent this?
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ACTH is very labile and sticks to glass!
-ADd aprotinin a protease inhibitor OR -Collect and separate cells immediately, put in plastic tube, and ship frozen-dry ice |
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What is the interpretation for the endogenous plasma ACTH assay in a dog with hyperadrenocorticism?
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<20 pg/ml=ADH
> 50 pg/mL=PDH 20-50=non diagnostic |
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What is the most common form of Cushing's?
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Pituitary dependent (80-85%)
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What causes pituitary dependent hyperadrenocorticism?
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Hyperplasia or microtumors of ACTH-secreting cells of pituitary
-Leads to too much ACTH and bilateral adrenal hyperplasia and too much cortisol |
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What causes adrenal dependent hyperadrenocorticism?
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Adrenal cortical tumor--> secretes cortisol autonomously- less ACTH is secreted by pituitary so other adrenal gland usually atrophies
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What is another cause of hyperadrenocorticism that's not ADH or PDH?
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Iatrogenic hyperadrenocorticism-exogenous glucocorticoids
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What are the 6 clinical signs associated with hyperadrenocorticism?
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1) PU/PD/PP
2) Pot-belly 3) bilaterally symmetrical alopecia 4) Cutaneous hyperpigmentation 5) Lethargy 6) Muscle wasting |
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What is the most common cause of equine "cushing's"?
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Functional adenoma of pars intermedia of pituitary gland
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What are 7 typical laboratory abnormalities seen with hyperadrenocorticism?
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1) Stress leukogram
2) Increased ALP 3) Mild polycythemia 4) Mild Increase ALT 5) Mild hyperglycemia 6) Hypercholesteremia +/- lipemia 7) Isosthenuria or hyposthenuria |
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What are the 3 screening tests for hyperadrenocorticism?
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1) ACTH stimulation
2) Low dose dexamethasone suppression 3) Urine cortisol: creatinine (normal rules out) |
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What are 2 differentiating tests for hyperadrenocorticism?
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High dose dexamethasone suppression test
Endogenous ACTH |
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What is the most commonly diagnostic test for Cushing's in horses?
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Overnight dexamethasone suppression test
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When should blood be taken for the baseline cortisol levels in a horse when preparing to perform an overnight DST? why? When should the Dex be given? Second sample?
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Uses normal circadian cortisol cycle so take blood for baseline around 5pm and give IM injection after
-Take second sample for plasma cortisol about 19 h later (noon) |
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What happens to normal horses that have the overnight dexamethasone suppression test performed? Cushingoid horses?
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-Normal: suppress to < 1 mg/dl and stay suppressed for at least 24 hours
-Cushingoid: typically suppress, but not as much as normal horses and cortisol rebounds more quickly |
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What causes hyperadrenocorticism in ferrets?
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Adrenal tumors or hyperplasia
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The screening tests used for hyperadrenocorticism in ferrets is different, what is the diagnosis based on?
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Based on increased:
-Estradiol -Androstenedione -17-OH-progesterone |
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What do they think is the cause of hypoadrenocorticism in dogs?
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Immune-mediated
-Rare in other species |
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What is iatrogenic hypoadrenocorticism?
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when exogenous steroids are discontinued and adrenals have atrophied
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What are the clinical signs of hypoadrenocorticism?
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Varies!
-Vomiting, diarrhea, collapse, weakness, lethargy, bradycardia |
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What are 7 lab abnormalities seen with hypoadrenocorticism?
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1) Hyponatremia and hyperkalemia- very common!!!
2) Na:K < 23:1 (very suggestive) or < 26:1 (somewhat suggestive) 3) Lymphocytosis & eosinophilia 4) Mild anemia 5) Prerenal azotemia 6) Mild hypercalcemia 7) Mild hypoglycemia |
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How is hypoadrenocorticism diagnosed?
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History, clinical signs, lab data, confirm w/ lack of response to ACTH stimulation
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