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Labs Medicine > Adrenal > Flashcards

Adrenal Flashcards

1
Q

What are the three zones of the adrenal cortex?

A

zona glomerulosa
zona fasciculata
zona reticularis

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2
Q

What hormones are made by the zona glomerulosa?

A

salts:

mineralocorticoids
aldosterone

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3
Q

What hormones are made by the zona fasciculata?

A

sugars

glucocorticoids
cortisol

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4
Q

What hormones are made by the zona reticularis?

A

sex steroids
progesteroid
androgens
estrogen precursors

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5
Q

What area is in the center of the adrenal gland?

A

medulla

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6
Q

What hormones are made by the medulla?

A

catecholamines

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7
Q

What does ACTH actually stimulate within the adrenal gland?

A

movement of choletserol into mitochondria where the CYP enzymes are located so it can be turned into hormone

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8
Q

What’s the classic triad for pheochromocytoma?

A

paroxysmal hypertension
headache
generalized sweating

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9
Q

What lab tests should be ordered to confirm a diagnosis of pheochromocytoma?

A
  1. 23 hr urine fractionated metanephrines
  2. 24 hr urine catecholamines
  3. plasma free fractionated metanephrines

(do just urine metanephrines if pre-test probability is low and all three if high)

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10
Q

What are metanephrines and why are they elevated in pheos?

A

Pheos are catecholamine-secreting tumors that arise from the adrenal medulla.

NE and Epi are metabolized to normetanephrine and metanephrine intratumorally and will then spill into the plasma and are excreted in excess into the urine

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11
Q

Why is the measurement of urine metanephrines preferred over measurement of plasma or urine catecholamines?

A

Intratumoral metabolism of the catecholamines occurs continuously and independently of catecholamine release, so the levels of metanephrines in the urine will be consistently elevated

catecholamine levels, on the other hand, will vary significantly as release varies; increasing significantly during paroxysms and then returning to normal in between

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12
Q

True or false: metanephrine levels correlate with pheo tumor size.

A

true!

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13
Q

Why are urine homovanillic acid (HVA) and vanillylmandelic acid (VMA) measured for the diagnosis of neuroblastoma and not metanephrines, since it is also a catecholamine-secreting tumor?

A

Neuroblastomas originate from sympathetic ganglion cells have contain MAO, but not COMT. This means they produce norepinephrine and dopamine, but no epinephrine

intratumoral inactivation of the NE and dopamine leads to HVA and VMA, not the metanephrines

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14
Q

Why aren’t HVA and VMA used for the diagnosis or monitoring of pheochromocytoma?

A

Dopamine-producing pheos are super rare, so HVA isn’t elevated

Pheos have MAO, but much much more COMT, so the VMA level is negligible compared to the VMA from metabolism of sympathetic nerve NE

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15
Q

What enzyme deficiency accounts for over 95% of congenital adrenal hyperplasia cases?

A

21-hydroxylase deficiency

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16
Q

Describe what happens to the hormone levels in 21-hydroxylase deficiency?

A

There is decreased to no cortisol production, so you get excessive ACTH

this then stimulates the adrenal cortex, but the precursors are shunted to the androgen biosynthetic pathway leading to the accumulation of progesterone and 17-hydroxyprogesterone

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17
Q

What’s the clinical presentation of 21 hydroxylase deficiency?

A

prenatal masculinization (ambiguous genitalia) in females and postnatal virilization in both sexes

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18
Q

What are the clinical and laboratory differences in patients with partial or complete 21-hydroxylase deficiency?

A

Mild form/partial: the increase in ACTH is able to keep cortisol at normal levels and the 17-OHP in excess causes only a mild salt-wasting with up-regulation of aldosterone in response

the Severe form/complete: low/no aldosterone or cortisol with dehydration due to salt wasting

19
Q

Very high levels of what precursor are diagnostic for 21 hydroxylase def?

A

17-hydroxyprogesterone

20
Q

What are the electrolyte abnormalities that can occur in classic congenital adrenal hyperplasia?

A

hyponatremia
hypochloremia
hyperkalemic acidosis

(due to the aldosterone deficiency - so this only occurs in complete enzyme loss)

21
Q

What’s considered the gold standard for diagnosing congenital adrenal hyperplasia?

A

ACTH cosyntropin stimulation test

22
Q

What is the second most common cause o congenital adrenal hyperplasia and what lab findings would be expected?

A

11-beta hydroxylase deficiency

elevated 11-deoxycortisol levels

23
Q

How does 11-beta hydroxylase deficiency differ from 21-beta hydroxylase deficiency clinically?

A

they both have ambiguous genitalia in females due to androgen excess, but 11-b hydroxylase deficiency also causes hypertension due to 11-deosycortisone’s action as a mineralocorticoid

you also get low renin which may result in HYPOkalemia instead of hyperkalemia

24
Q

What are the common signs and symptoms of hypercortisolism (Cushing’s syndrome)?

A 
truncal obesity
facial plethora
glucose intolerance
weakness
HTN
psych changes
easy brusing
hirsutism
oligo or amenorrhea
impotence
acne/oily skin
abdominal striae
ankle edema
polydipsia/polyuria
hyperpigmentation
headache
25
Q

Why do patients with Cushing’s syndrome become hypertensive?

A

cortisol and aldosterone have the same in vitro affinity for the mineralocorticoid receptor, but 11 beta hydroxysteroid dehydrgenase type 2 usually inactivates cortisol to prevent its action at the MR

however, with cortisol excess, this enzyme is overwhelmed, so you get activation of the MR with Na retention and HTN

26
Q

What three tests are recommended options to screen for Cushing’s syndrome?

A

24-hr urinary cortisol

late night salivary cortisol

overnight low dose dexamethasone suppression test (measure serum cortisol 9 hours later)

27
Q

What is on the differential diagnosis for Cushing’s syndrome?

A 
Cushing's disease (pituitary adenoma)
ectopic ACTH syndrome
Ectopic CRH syndrome
Adrenal adenoma
adrenal carcinoma
micronodular hyperplasia
macronodular hyperplasia
psueo-cushing's syndrome (major depressive disorder or alocoholism)
28
Q

How is the low-dose dexamethasone test performed and interpreted?

A

Dex inhibits ACTH production

Low dose (1 mg) is an overnight screening

patients with cushing’s syndrome will generally not suppress cortisol (however, some cases of cushing’s do suppress, so another test must be used to confirm diagnosis)

29
Q

What is the high dose dex suppression test and what is it used for clinically?

A

8 mg

used to differentiate Cushing’s disease from Cushing’s syndrome

ACTH secretion in CUshing’s disease is only relatively resistant to dex suppression, so in a pituitary adenoma, it will NOT suppress at low dose, but WILL suppress at high dose

(non-pituitary cancer doesn’t give a shit and will never suppress)

30
Q

Why is dexamethasone used in the suppression test and not other steroids?

A

measurement of cortisol is unaffected by dexamethasone, whereas other steroids cross-react with the cortisol assay and would give falsely elevated cortisol results

31
Q

Once Cushing’s SYNDROME has been confirmed, how do you establish the cause?

A

Measure the ACTH on 2 separate days (due to episodic nature of secretion)

32
Q

If ACTH is low, what should be the next step?

A

If ACTH is low, that means, it’s ACTH-independent Cushing’s syndrome and can’t be pituitary or ACTH-like

next step will be to check an Adrenal CT or mRI to look for an adrenal tumor secreting cortisol

33
Q

If the ACTH is intermediate, what should the next test be?

A

a corticotropin releasing hormone stimulation test.

Give the CRH and look to see what the ACTH level does.

34
Q

If the ACTH does not respond to the CRH stim test, what do you do?

A

go back down the low ACTH route and check an adrenal CT/MRI

35
Q

If the ACTH level does go up appropriately in the CRH test, what do you do?

A

You go down the workup path for an ACTH-dependent Cushing’s syndrome workup

36
Q

If you decide the patient has an ACTH-dependent cushing’s syndrome, what are your next two diagnostic options?

A

either the CRH stim and dex supp test

OR go straight to pituitary MRI

37
Q

If the pituitary MRI reveals a tumor, what is the next step?

A

an inferior petrosal sinus sampling for ACTH levels

38
Q

If there is no central step-up of ACTH from the IPPS, what’s the diagnosis?

A

ectopic ACTH secretion from some other cancer

39
Q

What are the common signs and symptoms of chronic adrenal insufficiency (Addison’s disease)?

A 
weakness/fatigue
anorexia
GI symptoms
salt craving
orthostatic hypotension
muscle/joint aches
weight loss
hyperpigmentation
vitiligo
auricular calcifications
40
Q

What lab abnormalities will be seen in addison’s disease?

A 
hyponatremia
hyperkalemia
hypercalcemia
azotemia
anemia
eosinophilia (interesting)
41
Q

What findings are helpful for distinguishing primary adrenal insufficiency from secondary or tertiary adrenal insufficiency?

A

Hyperpigmentation! It’s secondary to the elevated ACTH (increased MSH as a cleavage byproduct - increased melanin synthesis) - will ONLY be seen in primary adrenal insufficiency

mineralocorticoid deficiency only present in primary because aldosterone will be preserved in secondary and tertiary and can be stimulated by the RAS - means you won’t see the hyponatremic hyperkalemic hypotension

42
Q

What lab tests are used to establish a diagnosis of adrenal insufficiency?

A
  1. random 8 am serum cortisol and ACTH
  2. if abnormal, do an ACTH stim test (measure cortisol at baseline and after IV cosyntropin)
  3. if abnormal, eval for the underlying cause
43
Q

How do you go about evaluating for the underlying cause of primary adrenal insufficiency?

A
  1. measure anti-adrenal antibodies
  2. If CAH is suspected, measure adrenal androgens
  3. Screen for TB, adrenoleukodystrophy, adrenomyeloneuropathy, and adrenal hypoplasia congenita (whatever those are)

Labs Medicine (27 decks)

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