Hypothalamic Pituitary Lab Diagnositcs Flashcards Preview

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Flashcards in Hypothalamic Pituitary Lab Diagnositcs Deck (7):
1

1) A 45-year-old man seeks evaluation for weakness, fatigue, decrease of libido and loss of body weight. Laboratory tests reveal low plasma levels of ACTH and TSH. What is the most likely diagnosis and which laboratory tests would be the most appropriate for the patient?

Conclusion: Indicates a panhypopituitarism

Likely due to a hormone-negative macroadenoma of the pituitary gland that compresses the trophic cells. (Other reasons can inculde: blood supply, tumor growing nearby, mechanical damage due to trauma or stroke, storage disease with toxic material deposition).

 

Further tests:

Check serum levels of the other pituitary hormones, LH, FSH, PRL, GH

Do stimulation tests for ACTH and GH with CRH and GHRH. 

Do an MRI to check for tumors. 

 - Stimulation test for anterior pituitary hormones (e.g. GnRH for LH/FSH, synthetic ACTH for cortisol, TRH for TSH)
- Insulin tolerance test: adminster insulin to induce hypoglycemia (stress) to see if ACTH / cortisol and GH increase in plasma (hypothalamo-hypophyseal axis)
- X-ray / CT / MRI of head to check for pituitary adenoma
- Can also check for a decrease in posterior pituitary hormones (ADH / oxytocin) indicative of diabetes insipidus: water deprivation test and desmopressin test.

2

2) In a 29-year-old woman complaining of amenorrhea, plasma PL is found elevated in association with low FSH and LH levels. Estrogen excretion is decreased. GnRH stimulation test was performed on three consecutive days. The first two tests were negative but after the third test a normal response was detected in plasma FSH and LH. 
How do you interpret the result of the test and what is the most likely diagnosis?

It is probably a prolactinoma suppressing FSH and LH release.

The GnRH has to be released in a pulsatile manner, so on the 3rd day, the pulsation was sufficient to overcome the PRL inhibition and induce FSH and LH release. 

 

 

3

3) A 44-year-old man complains of impotence and galactorrhea. He has gynecomasty.
Plasma PL is very high, FSH and LH are lower than normal. Plasma testosterone and urinary 17-ketosteroid excretion are decreased. After TRH or chlorpromazine stimulation there is only a minimal increase in plasma PL. What is the most likely diagnosis and what other tests would you perform?

Urinary 17-ketosteroids are a degradation product of Androgens

Diagnosis is again likely a prolactinoma.

 

Perform a suppression test. Dopamine is effective at reudcing prolactinoma release. 

Perform MRI to locate prolactinoma

Treat with Bromocriptine (dopamine analog) or irradiation. 

4

4) A 51-year-old man seeks evaluation for blurring of vision and headache. He has coarse facial features and enlarged extremities. The determination of which hormone would be the most straightforward in the patient? What other diagnostic procedure(s) would you order?

Its probably acromegaly. IGF-1 measurement is most straightforward. IGF-1 levels are more constant, while GH is more pulsatile and variable. 

MRI or CT for a hypothalamic/perichiasmatic tumor

Glucose suppression test by GH administration, glucose suppression by GH is lost in acromegaly. 

Opthamalogical testing to examine his feild of vision

5

5) In a 35-year-old woman, after the third delivery, lactation fails to start. She complains of loss of body weight and amenorrhea. Low voltage is found in her EKG tracing. Plasma levels of anterior pituitary hormones are very low. FT4 and FT3 are low. After TRH stimulation test neither TSH nor PL increase. Serum cholesterol level: 8.6 mmol/l. Is the problem primary, secondary or tertiary?

Sheehan syndrome causing panhypopituitarism. Secondary level problem.  Hypothalamus is tertiary, pituitary is secondary, gonads, adrenals, thyroids are primary. 

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6) A 37-year-old man complains of intense thirst (anadipsia) which commenced 7 days before. He drinks 5–6 l water a day, preferentially chilled water. His urine output is 6 l/24 h, the density is 1.004 kg/l. He is subjected to a water deprivation test with a duration of 8 h. During the test period he voids 4 l urine and the density does not exceed 1.005 in any of the collected fractions. What is the most likely diagnosis and which test would be the most effective in the differential diagnosis?

Lab findings: His urine fails to concentrate during the water deprivation test (plasma osmolality concentrates instead). 

The patient has diabetes insipidus. 

Further tests:

Administration ADH analog

if urine concentrates, it is a central diabetes insipidus or central psychogenic polydipsia/adh inhibition.  /

if urine does not concentrate, it is peripheral/nephrogenic diabetes insipidus (ADH insensitivity).

Check for Pyschogenic Polydipsia, or physiological ADH inhibition by salt loading, which will cause ADH release due to blood concentration and should halt his urination. 

7

7) A 50-year-old woman complains of polyuria. She drinks 6–8 l water a day.

Serum Na+: 138 mmol/l,

urine output: 8 l/24 h,

density: 1.004 kg/l.

After salt loading urine volume decreases and the density increases. What is the most likely diagnosis?

Plasma Na concentration is normal 135-145 mM

Salt loading inhibited urination and increased density --> Pyschogenic polydipsia.