Chempath - Pituitary

Question 1

What stimulates and inhibits the release of prolactin?

Answer 1

Stimulates - TRH, Inhibits - Dopamine

Question 2

What are the components of a combined pituitary function test?

Answer 2

LHRH (GnRH), TRH and insulin

Question 3

When do you measure CPFT?

Answer 3

At 0 mins and then every 30 mins for 2 hours.

Question 4

Contraindications and SEs of CPFT

Answer 4

Contraindications: cardiac disease (need normal ECG), epilepsy, untreated hypothyroidism (impair GH and cortisol response)

SEs:
Hypoglucaemia - sweating, palps, LOC (adrenergic sx). Rarely - convulsions (–> give 50ml 20% dextrose, ensure good IV access prior to test). G <1.5 may cause neuroglycopenia –> aggression.
TRH - transient metallic taste, flushing, nausea

Question 5

What test needs to be done to confirm acromegaly?

Answer 5

OGTT. IGF-1 - sensitive but not specific. Rx= ocreotide

Question 6

In the insulin tolerance test part of CPFT, what are the adequate cortisol and GH responses?

Answer 6

Cortisol: rise greater than 170nmol/l to above 550mM
GH: rise greater than 10IU/l

Question 7

In the thyrotrophin releasing hormone test part of CPFT, what is the normal result?

Answer 7

The normal result is a TSH rise to >5 mU/l (30 min value > 60 min value)
Hyperthyroidism = TSH remains suppressed
Hypothyroidism = exaggerated response.

Dynamic testing not usually required to diagnose.

Question 8

In the gonadotrophin releasing hormone test part of CPFT, what is the normal result?

Answer 8

Normal peaks can occur at either 30 or 60 minutes - LH should > 10 U/l and FSH should > 2 U/l.

Gonadotrophin deficiency is diagnosed on the basal levels rather than the dynamic response.

Question 9

What is the size cut off for micro vs macro adenoma?

Answer 9

Microadenoma < 10mm, usually benign

Macroadenoma > 10mm, aggressive

Question 10

How do you distinguish between hyperprolacinaemia caused by stalk compression vs prolactinoma?

Answer 10

Mild high prolactin –> non-functioning tumour –> stalk compression –> blockage of inhibitory dopamine

Significantly raised prolactin –> prolactinoma –> Rx bromocriptine/cabergoline

Question 11

Causes of excess ADH

Answer 11

Lung - lung paraneoplasias – usually small cell lung cancer, pneumonia
Brain - Traumatic brain injury, meningitis, primary or secondary tumours
Iatrogenic – SSRIs, Amitryptiline, carbamazepine, PPIs
Effect – SIADH – Euvolaemic Hyponatraemia

Question 12

Causes of reduced ADH

Answer 12

Diabetes insipidus –increased diuresis due to either failure of production or insensitivity to ADH, leads to decreased urine osmolality and increased serum osmolality

Neurogenic – Failure of production – 50% idiopathic
Nephrogenic – commonly iatrogenic – lithium, also hypercalcaemia, renal failure
Dipsogenic (psychogenic polydipsia) – Failure/damage to hypothalamus and thirst drive, hypernatraemia without increased thirst response.