Flashcards in Week 26: HPO Axis Deck (15)
At pt demonstrates elevated prolactin. What is the order of investigation?
1. Rule out pregnancy
2. Repeat prolactin level to rule out misreading due to stress/satiation/exercise
3. Obtain detailed drug history to rule out medication effect
4. Ensure no renal insufficiency
5. If prolactin is persistently elevated, image with MRI or CT if MRI is not available.
Why isn't GH a good test?
Released in a pulsatile fashion. Use IGF-1 instead.
24 hour urine cortisol.
Screen for Cushing's.
- integrated measurement of free cortisol
- The higher the value (2-3 times more than normal), the more certain of Cushing's
- results can be normal in early/mild disease
How should we screen for Cushings?
1. 24 hour urine cortisol.
2. Overnight dexamethasone suppression test
Overnight dexamethasone test
Screen for Cushing's.
- Bolus of dexamethasone at midnight and measure serum cortisol at 8am
- The lower the measured cortisol, the more certain we can be at ruling out cushing's
When might overnight dexamethasone test give you a false positive?
Increased CBG (OCP, estrogen, pregnancy);
Lower dexamethasone levels (poor absorption, drugs that induce metabolism);
10% of normal people have hypointensities that are consistent with pituitary adenoma.
What to do if you discover a pituitary incidentaloma
Scan to see if it is functioning.
If it is a macroadenoma, scan for hypopituitarism and check visual fields if it is close to the optic chiasm.
Follow up imaging in the next year.
Why is it important to establish a biochemical and clinical diagnosis before imaging?
10% of the population has an incidentaloma. If you jump to imaging you might find one of those and be misled!
First line therapy for prolactin-producing tumors?
First line treatment for functioning pituitary tumours (other than a prolactin-secreting tumor) and symptomatic non-functioning tumor
common causes of goitre in order
1. iodine deficiency
4. multinodular disease
a benign neoplasm derived from follicular cells. More common in women
older than 30.
Do not require further workup unless they are growing or compressive.
How does prolactin cause testosterone insufficiency?
Prolactin inhibits GnRH, thus interfering with release of LH and FSH. LH is responsible for stimulating Leydig cells to synthesize testosterone from cholesterol (a series of steps)