Pathophysiology of the Adrenal Glands: Diagnostics and Cases

Question 1

what are some tests to screen for adrenocortical diseases?

Answer 1

baselines cortisol level
urine cortisol:creatinine ratio
function tests

Question 2

what are some function tests for screening for adrenocortical diseases?

Answer 2

ACTH stimulation test
low-dose dexamethasone suppression test
TRH stimulation test: equines only

Question 3

what are some tests to test for the etiology of adrenocortical diseases?

Answer 3

high-dose dexamethasone suppression test
endogenous ACTH level
advanced imaging

Question 4

what is the secretion of ACTH and cortisol like?

Answer 4

pulsatile

Question 5

is basal cortisol useful for diagnosis of hyperadrenocorticism?

Answer 5

no: while cushing’s causes excess levels of cortisol, single baseline cortisol often falls in the normal range

Question 6

what can high-normal basal cortisol rule out?

Answer 6

hypoadrenocorticism

Question 7

what is urine cortisol:creatinine ratio used to rule out?

Answer 7

hyperadrenocorticism

Question 8

what is the test of choice for diagnosing hypoadrenocorticism?

Answer 8

ACTH stimulation test

Question 9

what should cause an exaggerated response to ACTH stimulation?

Answer 9

cushing’s
no longer recommended to diagnose cushing’s

Question 10

what is the ACTH stimulation test like?

Answer 10

relatively specific: 15% false positives
not very sensitive
positive test does not indicate etiology

Question 11

how do you perform a low-dose dexamethasone suppression test?

Answer 11

give dexamethasone and measure cortisol

Question 12

what does a low-dose dexamethasone suppression test evaluate?

Answer 12

responsiveness of pituitary to physiologic levels of negative feedback

Question 13

is a low-dose dexamethasone suppression test used to diagnose addison’s?

Answer 13

no

Question 14

how sensitive is a low-dose dexamethasone suppression test?

Answer 14

very sensitive: 98% in dogs
90% in cats
not used in horses due to fear of developing laminitis

Question 15

what cortisol concentrations do healthy dogs have at 8 hours with a low-dose dexamethasone suppression test?

Answer 15

<1.4 micrograms/dL

Question 16

a high-dose dexamethasone suppression test should not be performed on animals in which _______________________________

Answer 16

the clinical diagnosis is uncertain

Question 17

how many canine pituitary tumors do not suppress with high-dose dexamethasone suppression test?

Answer 17

25-30%

Question 18

what can an endogenous ACTH level be used to help determine?

Answer 18

cause of hyperadrenocorticism
cause of hypoadrenocorticism

Question 19

what can resting ACTH be a good screening test for in horses?

Answer 19

equine pituitary pars intermedia dysfunction
horses with PPID have higher ACTH values than normal horses

Question 20

what can thyrotropin releasing hormone stimulation test be used to diagnose in horses?

Answer 20

early equine pituitary pars intermedia dysfunction

Question 21

who produces POMC?

Answer 21

corticotrophs in pars distalis and melanotrophs in pars intermedia

Question 22

what is the procedure of a TRH stimulation test?

Answer 22

measure basal ACTH level
measure ACTH 10 minutes after administration of thyrotropin releasing hormone

Question 23

what are some causes of hypercholesterolemia?

Answer 23

hyperadrenocorticism
hypothyroidism
liver disease with cholestasis
nephrotic syndrome
diabetes mellitus
pancreatitis

Question 24

in hyperadrenocorticism, who is increased ALP activity seen in?

Answer 24

dogs

Question 25

is urine cortisol:creatinine ratio a screening or diagnostic test?

Answer 25

screening: if consistent with hyperadrenocorticism, need to further work up

Question 26

true/false: a "normal" ACTH stimulation test does not rule out hyperadrenocorticism

Answer 26

true

Question 27

what pattern with the LDDS test indicates a pituitary-dependent hyperadrenocorticism?

Answer 27

cortisol <1.4 micrograms/dL at 4 hours >1.4 at 8 hours

Question 28

in a high dose dexamethasone suppression test, does failure to suppress rule out a pituitary tumor?

Answer 28

no: not diagnostic for hyperadrenocorticism due to adrenal tumor

Question 29

if a test is highly sensitive, a negative test is _______________________

Answer 29

extremely useful

Question 30

if a test is highly specific, a positive test is _________________________

Answer 30

extremely useful

Question 31

is basal cortisol a useful test for diagnosis of hyperadrenocorticism?

Answer 31

no single baselines cortisol often falls in the normal range

Question 32

what can high-normal basal cortisol rule out?

Answer 32

hypoadrenocorticism

Question 33

why are false positives of urine cortisol:creatinine ratio common?

Answer 33

chronic stress/disease

Question 34

why is an ACTH stimulation test no longer indicated for diagnosing Cushing's?

Answer 34

may miss the diagnosis of early pituitary dependent hyperadrenocorticism if adrenal hyperplasia has not yet occurred changes happen over time

Question 35

does a low-dose dexamethasone suppression test provide etiology?

Answer 35

maybe

Question 36

in a low-dose dexamethason suppression test, healthy dogs have cortisol concentrations of ______________ at 8 hours

Answer 36

<1.4 micrograms/dL

Question 37

animals with PDH would have cortisol levels _________________ at 4 or 8 hours with a high-dose dexamethasone suppression test

Answer 37

<1.4 micrograms/dL adrenal tumor stays high

Question 38

which canine pituitary tumors do not suppress with high-dose dexamethasone suppression test?

Answer 38

pars intermedia tumors lack portal blood supply large, poorly differentiated pars distalis tumors

Question 39

do you need to determine etiology for horses with cushing's?

Answer 39

no

Question 40

what would you expect the endogenous ACTH level to be in an animal with an adrenal tumor causing hyperadrenocorticism?

Answer 40

<20 pg/mL low

Question 41

what would you expect the endogenous ACTH level to be in an animal with PDH?

Answer 41

normal to elevated <20, 20-45, >45 pg/mL

Question 42

what is endogenous ACTH level a good screening test for?

Answer 42

equine pituitary pars intermedia dysfunction

Question 43

what levels of endogenous ACTH do horses with pituitary pars intermedia dysfunction have?

Answer 43

higher

Question 44

what is the seasonal variation of endogenous ACTH in horses?

Answer 44

Nov-July: <15 pg/mL Aug-Oct: <30 pg/mL

Question 45

what does the endogenous ACTH level test use for a tube?

Answer 45

EDTA plasma plastic cold or frozen

Question 46

what are the differentials for a Na/K ratio < 25 or 22?

Answer 46

hypoadrenocorticism renal disease ruptured bladder diabetes with ketoacidosis severe diarrhea

Question 47

what are some causes of hypoglycemia?

Answer 47

hypoadrenocorticism artifact: metabolized by red blood cells hyperinsulinism sepsis/endotoxemia underproduction of glucose

Question 48

what are some causes of increased alkaline phosphatase activity?

Answer 48

cholestasis bone isoenzyme drug induction cortisol induced production of isoenzyme: dogs

Question 49

what are some causes of hypercholesterolemia?

Answer 49

hyperadrenocorticism hypothyroidism liver disease with cholestasis nephrotic syndrome diabetes mellitus pancreatitis

Question 50

does failure to suppress during a high-dose dexamethasone suppression test rule out a pituitary tumor?

Answer 50

no