Endocrinology - Thyroid, pituitary Flashcards
with regards to glandular abnormality, primary refers to ?
refers to the gland that secretes the hormone
With regards to glandular abnormalities, secondary refers to?
refers to the disease of the gland that controls the primary gland
With regards to glandular abnormalities, tertiary refers to?
the disease of the gland that controls the gland that controls the primary gland
what is the difference between the anterior and posterior pituitary control?
- the hypothalamus uses hormones to control the anterior pituitary
- hypothalamus uses direct nerve stimulation to control the posterior pituitary.
what hormones does the posterior pituitary contain?
It stores and releases oxytocin and ADH (vasopressin).
what is the formula for serum osmolality?
2Na + glucose/18 + BUN/2.8
what triggers ADH to be released?
- volume contraction
- nausea
what decreases the threshold for ADH to be released?
pregnancy and pre-menses
what increases the threshold set for ADH to be released?
- chronic hypervolemia
- acute hypertension
- corticosteroids
what hormones does the anterior pituitary contain?
- FSH
- LH
- ACTH
- TSH
- Prolactin
- Growth Hormone
what are the two types of signals that control the release of anterior pituitary hormones?
- stimulatory hormones produced by the hypothalamus
- target organ hormone feedback
basics of ACTH? peaks?
- diurinary variation with peak 3-4AM and nadir at 10-11pm
ACTH increase in response to CRH and stress - ACTH stimulates the adrenal gland to produce corticosteroids and androgens
- stimulates adrenal cortex which produces glucocorticoids
- cortisol inhibits CRH and ACTH
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basics of GH?
- pulsatile fashion
- regulated by GHRH and somatostatin
- GHRH cause release of GH from the pituitary
- somatostatin/GHIH inhibits the release of GH from the pituitary
- somatostatin/GHIH also inhibit release of TSH from pituitary
basics of LH and FSH?
- produced by gonadotrophs, regulated by pulsatile secretion of GnRH from the hypothalamus
- LH stimulates the secretion of sex steroids from gonads. In testes, LH binds to Leydig cell receptors to produce and secrete testosterone. THeca cells in ovary respond to LH by secretion of testosterone, which is converted into estrogen by adjacent granulosa cells.
- FSH stimulates maturation of ovarian follices and helps for sperm production.
- testosterone, estrogen and progesteorne both inhibit pituitary LH and FSH and hypothalamus GNRH
basics of prolactin regulation?
- under tonic inhibition by hypothalamic dopamine, only secreted when brake is released.
- positively regulated by TRH, GRH, and VIP. Estrogens too. (VEG-T)
- stimulation of nipples and mammary gland stimulates prolactin-stimulating hormones from the hypothalamus too.
basics of TSH regulation?
TSh secretion stimulated by hypothalamic TRH and inhibited by T3/T4 and somatostatin/GHIH
what is the first step to determine a pituitary tumor?
- if it is functionally abnormal
- if it is secreting abnormal amount of any hormone
what are the mass effect symptoms of pituitary tumor?
headache, diplopia, or visual field defects (bitemporal hemianopsia), and seizures.
you suspect pituitary tumor, what test/lab are you going to order?
- MRI to see tumor
- Prolactin
- IGF_1 to screen for acromegaly
- 24-hour urine free cortisol concentration or 1 mg overnight dexamethasone (if cortisol excess) or ACTH stim (if cortisol deficiency)
- TSH and T4
- alpha subunit, FSH, and LH
what is alpha subunit for pituitary tumor?
support diagnosis of gonadotroph adenoma, suggest mass is the pituitary origin.
define hyperprolactinemia?
prolactin level >20 ng/ml
prolactin level of 21-40 can be caused by?
- dopamine antagonists (antipsychotics, verpamil etc)
- pregnancy or estrogen use
- CKD
- hypothyroidism
- sarcoidosis and trauma (interfere with production/dopamine transport)
- food intake
- chest wall injuries/nipple stimulation in lactating women
describe what separates micro vs maroadenoma?
microadenoma<1cm; macroadenoma 1cm and higher (bigger - visual defects)
describe the pathophysiology of elevated prolactin level and resultant symptoms?
- elevated PRL causes decrease release of GnRH
- decreased GnRH causes decrease in LH and FSH
- Decrease LH and FSH causes ED ,amenorrhea, hirsutism
what is the treatment for prolactinomas?
- dopamine agonists like cabergoline and bromocriptine which reduce both PRL level and tumor size.
- transsphenoidal surgery if refractory
- Can use both in pregnancy (1/3 of macroadenomas enlarge)
what are the important side effects specific to cabergoline?
increased cardiac valvulopathy in high doses.
contraindicated in patients with known lung, heart valve, and retroperitoneal fibrotic disease.
what is growth hormone suppressed by?
hyperglycemia, somatostatin, chronic corticosteroid use
what is growth hormone stimulated by?
hypoglycemia and estrogens
what is the most important long term problem associated with acromegaly?
cardiovascular disease, OSA, DM2, colon polyps
how do you screen and confirm for acromegaly? what else do you need to check?
- screen by checking the adjusted IGF-1 level
- Confirm by failure to suppress GH after 75gm OGTT
- Post OGTT GH level>1 is dx of acromegaly.
- check prolactin which may be elevated due to co-secretion in 25% of GH tumors
- large tumors can disrupt thyroid and gonadotropin release, so levels may need to be assessed too.
how do you treat acromegaly?
- treat all patients even asymptomatic with transphenoidal surgery
- give somatostatin analogs (octreotide) +/- dopamine agonsits (bromocriptine or carbergoline) or GH receptor antagonists as adjuvant tx for residual tumor.
- Screen with colonoscopy and echocardiogram regardless of age.
what suggests a gonadotroph adenoma?
increase in free alpha subunits or high levels of FSH and/or LH
which cancers mets to the pituitary?
- breast and lung cancer is the most common
- lymphoma and leukemia can present as primary
how does pituitary cancer mets present?
presents as Diabetes inspidus
what is the work up for pituitary incidentaloma?
- test visual fields for tumors that impinge on optic nerve
- Measures PRL to r/o prolactinomas
- IGF-1 to screen for acromegaly
- 24 hour urine free cortisol or low dose dexa test
- TSH and FT4
- morning cortisol to assess for hyposecretion
- LH, FSH and testosterone
what is the clinical presentation fo pituitary apoplexy? labs and imaging?
- pituitary bleeding
- suspect when variable neuro symptoms with fluctuating symptoms
- decreased ACTH and cortisol levels
- on cosyntropin stimulation, cortisol levels increase since adrenals remain intact.
- imaging shows a high density mass in sella
what are the two types of DI? Explain the difference?
- nephrogenic DI - decreased ADH effect on the kidneys
- Neurogenic DI - decreased ADH production
what are the main causes of nephrogenic DI?
- electrolytes: hypercalcemia, hypokalemia
- Medications: loops diuretics, lithium
- interstitial: sickle cell, Sjogren’s
what are the important causes of neurogenic DI?
- genetic (50%)
- Acquired: hypopituitarism, CNS injury,
- infiltrative diseases (sarcoidosis, wegners, eosinophilic grnuloma etc)
what are the symptoms of DI?
- polyuria (high urinary output)
- polydypsia (excessive thirst)
- nocturia is usually the first symptom
what do you see on labs for DI?
- low urine osm
- normal to high serum osmolality
how do you differentiate neurogenic vs nephrogenic DI with water deprivation?
- with water deprivation, measure ADH and plasma osmolality
- If ADH does not increase with increase plasma osmolality, this is neurogenic DI
- If ADH increases with but no increase in urine osm, this is nephrogenic DI.
- If urine fails to concentrate with water restriction and desmopressin, this is also nephrogenic DI.
how do you treat nephrogenic DI?
low sodium diet and thiazide diuretics +/- amiloride
how do you treat neurogenic DI?
desmopressin
high TSH, low FT4 ddx?
- primary hypothyroidism
- chronic lymphocytic thryoiditis (hashimotos)
high TSH, high FT4 ddx
- Pituitary (secondary; TSH induced)
- hyperthyroidism
- thyroid hormone resistance syndromes
Low TSH, high FT4 ddx?
- Euthyroid sick syndrome (primary hyperthyroidism)
- subacute or silent thyroiditis
Low TSH, normal FT4 ddx?
- Euthyroid sick syndrome
- subclinical hyperthyroidism
- multinodular goiter with autonomous production
Low TSH, low FT4 ddx?
pituitary hypothryoidism
when is RAIU increased?
- Graves disease
- TSH pituitary tumor
- Hot nodules (solitary, TMN)
- HcG secreting tumor
- Iodine deficiency
when is RAIU decreased?
- Thryoiditis
- excess exogenous T4 or T3
- iodine excess (contrast, dye, diet, amiodarone)
- Factitious hyperthyroidism
what is the purpose of a thyroid scan?
- Scintigraphy where you can see isotopes localize in the thyroid.
- used in the work up for hyperthyroidism
- shows hot - hyperfunctioning vs cold (underfunctioning).
what is the difference between thyroid uptake vs thyroid scan vs US?
- thyroid RAIU - gives you a number
- Thyroid scan assess for goiter and nodular disease (hot vs. cold)
- US determines size and number of nodules - cystic vs solid
when do you suspect secondary or tertiary hypothyroidism?
- low or inappropriately normal TSH with low FT4 except in hospitalized patients with multiple hormone deficiencies
- Differentiate secondary and tertiary by imaging the sella.
what conditions/drugs interfere with absorption of thyroxine?
- these cause increased TBG or increase the metabolism of T4, which can cause elevated TSH
- malabsorption syndromes
- estrogens
- cholestyramine
- iron/calcium/aluminum supplements
- resin binders
what are the two thyroid emergencies?
- myxedema coma
- thyroid storm
what signs and symptoms are suggestive of myxedema coma?
- decreased mentation and hypothermia
- Slowing of systemic processes (hypoventilation, hypoglycemia, bradycardia, hypoventilation)
what labs are suggestive of hypothyroidism outside of TSH?
- hyponatremia,
- normocytic anemia,
- hyperlipidemia (increased TC, LDL)
- pericardial effusions (rare)
- increased prolactin level (<100)
patient has elevated prolactin and amenorrhea, what do you need to check?
- check thyroid function as if hypothyroid, it will resolve with treatment.
- If not hypothryoid, do prolactin work up.
if you suspect myxedema coma, what labs do you need to draw?
- TSH and Ft4
- baseline cortisol and ACTH to rule coincident adrenal insufficiency
what is the empiric treatment for myxedema coma?
- Treat with either T3 as possible rapid onset and decrease conversion to T4 to T3 or T4
- empiric glucocorticoids until stim testing available
- empiric broad spectrum abx until the infection is excluded.
- passive rewarming if needed.
outside of TSH, what are abnormal labs/studies for hyperthyroidism?
- low TC and LDL
- normocytic/normochromic anemia
- hypercalcemia with increased bone alk phos
- osteopenia/osteoperosis
- increased CO, DCM, any tachyarrhythmia
what is apathetic hyperthyroidism?
commonly seen in elderly patients, new onset Afib or depression.