Pathophysiology of the Adrenal Glands: Diagnostics and Cases Flashcards
what are some tests to screen for adrenocortical diseases?
baselines cortisol level
urine cortisol:creatinine ratio
function tests
what are some function tests for screening for adrenocortical diseases?
ACTH stimulation test
low-dose dexamethasone suppression test
TRH stimulation test: equines only
what are some tests to test for the etiology of adrenocortical diseases?
high-dose dexamethasone suppression test
endogenous ACTH level
advanced imaging
what is the secretion of ACTH and cortisol like?
pulsatile
is basal cortisol useful for diagnosis of hyperadrenocorticism?
no: while cushing’s causes excess levels of cortisol, single baseline cortisol often falls in the normal range
what can high-normal basal cortisol rule out?
hypoadrenocorticism
what is urine cortisol:creatinine ratio used to rule out?
hyperadrenocorticism
what is the test of choice for diagnosing hypoadrenocorticism?
ACTH stimulation test
what should cause an exaggerated response to ACTH stimulation?
cushing’s
no longer recommended to diagnose cushing’s
what is the ACTH stimulation test like?
relatively specific: 15% false positives
not very sensitive
positive test does not indicate etiology
how do you perform a low-dose dexamethasone suppression test?
give dexamethasone and measure cortisol
what does a low-dose dexamethasone suppression test evaluate?
responsiveness of pituitary to physiologic levels of negative feedback
is a low-dose dexamethasone suppression test used to diagnose addison’s?
no
how sensitive is a low-dose dexamethasone suppression test?
very sensitive: 98% in dogs
90% in cats
not used in horses due to fear of developing laminitis
what cortisol concentrations do healthy dogs have at 8 hours with a low-dose dexamethasone suppression test?
<1.4 micrograms/dL
a high-dose dexamethasone suppression test should not be performed on animals in which _______________________________
the clinical diagnosis is uncertain
how many canine pituitary tumors do not suppress with high-dose dexamethasone suppression test?
25-30%
what can an endogenous ACTH level be used to help determine?
cause of hyperadrenocorticism
cause of hypoadrenocorticism
what can resting ACTH be a good screening test for in horses?
equine pituitary pars intermedia dysfunction
horses with PPID have higher ACTH values than normal horses
what can thyrotropin releasing hormone stimulation test be used to diagnose in horses?
early equine pituitary pars intermedia dysfunction
who produces POMC?
corticotrophs in pars distalis and melanotrophs in pars intermedia
what is the procedure of a TRH stimulation test?
measure basal ACTH level
measure ACTH 10 minutes after administration of thyrotropin releasing hormone
what are some causes of hypercholesterolemia?
hyperadrenocorticism
hypothyroidism
liver disease with cholestasis
nephrotic syndrome
diabetes mellitus
pancreatitis
in hyperadrenocorticism, who is increased ALP activity seen in?
dogs
is urine cortisol:creatinine ratio a screening or diagnostic test?
screening: if consistent with hyperadrenocorticism, need to further work up
true/false: a “normal” ACTH stimulation test does not rule out hyperadrenocorticism
true
what pattern with the LDDS test indicates a pituitary-dependent hyperadrenocorticism?
cortisol <1.4 micrograms/dL at 4 hours
>1.4 at 8 hours
in a high dose dexamethasone suppression test, does failure to suppress rule out a pituitary tumor?
no: not diagnostic for hyperadrenocorticism due to adrenal tumor
if a test is highly sensitive, a negative test is _______________________
extremely useful
if a test is highly specific, a positive test is _________________________
extremely useful
is basal cortisol a useful test for diagnosis of hyperadrenocorticism?
no
single baselines cortisol often falls in the normal range
what can high-normal basal cortisol rule out?
hypoadrenocorticism
why are false positives of urine cortisol:creatinine ratio common?
chronic stress/disease
why is an ACTH stimulation test no longer indicated for diagnosing Cushing’s?
may miss the diagnosis of early pituitary dependent hyperadrenocorticism if adrenal hyperplasia has not yet occurred
changes happen over time
does a low-dose dexamethasone suppression test provide etiology?
maybe
in a low-dose dexamethason suppression test, healthy dogs have cortisol concentrations of ______________ at 8 hours
<1.4 micrograms/dL
animals with PDH would have cortisol levels _________________ at 4 or 8 hours with a high-dose dexamethasone suppression test
<1.4 micrograms/dL
adrenal tumor stays high
which canine pituitary tumors do not suppress with high-dose dexamethasone suppression test?
pars intermedia tumors lack portal blood supply
large, poorly differentiated pars distalis tumors
do you need to determine etiology for horses with cushing’s?
no
what would you expect the endogenous ACTH level to be in an animal with an adrenal tumor causing hyperadrenocorticism?
<20 pg/mL
low
what would you expect the endogenous ACTH level to be in an animal with PDH?
normal to elevated
<20, 20-45, >45 pg/mL
what is endogenous ACTH level a good screening test for?
equine pituitary pars intermedia dysfunction
what levels of endogenous ACTH do horses with pituitary pars intermedia dysfunction have?
higher
what is the seasonal variation of endogenous ACTH in horses?
Nov-July: <15 pg/mL
Aug-Oct: <30 pg/mL
what does the endogenous ACTH level test use for a tube?
EDTA plasma
plastic
cold or frozen
what are the differentials for a Na/K ratio < 25 or 22?
hypoadrenocorticism
renal disease
ruptured bladder
diabetes with ketoacidosis
severe diarrhea
what are some causes of hypoglycemia?
hypoadrenocorticism
artifact: metabolized by red blood cells
hyperinsulinism
sepsis/endotoxemia
underproduction of glucose
what are some causes of increased alkaline phosphatase activity?
cholestasis
bone isoenzyme
drug induction
cortisol induced production of isoenzyme: dogs
what are some causes of hypercholesterolemia?
hyperadrenocorticism
hypothyroidism
liver disease with cholestasis
nephrotic syndrome
diabetes mellitus
pancreatitis
does failure to suppress during a high-dose dexamethasone suppression test rule out a pituitary tumor?
no
