ChemPath - Pituitary Flashcards
Explain why pituitary failure does not cause hypotension
It is the loss of aldosterone that would cause hypotension
In pituitary failure, the adrenals are still able to produce aldosterone
What hormones are produced by the hypothalamus and pituitary gland
GHRH → GH
TRH → TSH, prolactin
GnRH → FSH, LH, prolactin
CRH → ACTH
Dopamine - prolactin (-ve)
How do patients with pituitary failure present
Very few signs
Galactorrhoea
Amenorrhoea
Bitemporal hemianopia (>1cm macroadenoma)
What level of prolactin is suggestive of prolactinoma and why may prolactinoma become a problem
> 6000 prolactin - only cause will be a prolactinoma
Usually not a problem until it grows and interferes with production of the other hormones
What is the combined pituitary function test (Triple Test)
Used to measure pituitary function via measurement of glucose, cortisol, GH, FSH, LH, TSH, prolactin, and T4 after giving stimulatory hormones
- Insulin → hypoglycaemic stress
- CRH ↑ → ACTH ↑→ Cortisol ↑
- GHRH ↑ → GH ↑ - TRH
- TSH ↑ + prolactin ↑ → T4 ↑ - GnRH/LHRH
- LH, FSH ↑
What are the precautions taken before a combined pituitary function test
Check glucose regularly
Ensure an adequate hypoglycaemia (<2.2mM) to trigger stress
If severe hypoglycaemia occurs (or unconsciousness), rescue patient with 50mL of 20% dextrose
Check they are NOT epileptic (CI)
Check ECG prior to testing (CI)
Describe the method for the combined pituitary function test
- Fast patient overnight
- Ensure good IV access
- Weight pt. and calculate dose of insulin required
- Mix and IV Inject the following (patient may vomit on injection):
i. Insulin 0.15U/kg
ii. TRH 200mcg
iii. LHRH/GnRH 100mcg - Take bloods at 0, 30 and 60 minutes of glucose, cortisol, GH, LH, FSH, TSH, prolactin and T4
- Take bloods at 90 and 120 minutes of glucose, cortisol and GH
- Replacement: hydrocortison
What can be done to induce stress in children instead of insulin
Exercise
How is hypoglycaemia defined and how may it present
<2mM
1. Aggression
2. loss of consciousness/confusion
What is the management for a large prolactinoma that is causing pituitary failure
Macro: Trans-sphenoidal resection
+ replacement
1. Hydrocortisone (URGENT)
2. Thyroxine replacement
3. Oestrogen replacement
4. GH replacement (if young and growing)
How would you differentiate between a prolactinoma and non-functioning pituitary adenoma
Prolactinoma - prolactin levels >6000
NFPA - prolactin is raised, but not >6000
This is due to the adenoma pressing on the pituitary stalk and preventing dopamine from reaching the anterior pituitary → no -ve inhibition on prolactin release → secondary hyperprolactinaemia
How do you test for acromegaly
OGTT (75g glucose after fasting→ measure in 2h)
- GH should drop after being given glucose but in acromegaly there is a paradoxical rise
IGF-1 levels
- Produced in the liver in response to glucose
What is the management of acromegaly
Pituitary surgery (the best treatment option)
Pituitary radiotherapy
Cabergoline
Octreotide (somatostatin analogue; good at reducing the size of the tumour)
What are the contraindications to the combined pituitary function test
Epilepsy
Cardiac disease
Untreated hypothyroidism
What is the expected response from the combined pituitary function test
Insulin → ↓glucose, ↑GH, ACTH, cortisol (170-500)
TRH → ↑TSH (>5), prolactin
GnRH → ↑FSH (>10), LH (>2)
