ChemPath: Pituitary Flashcards

1
Q

Why doesn’t hypopituitarism cause low blood pressure?

A

The adrenals are still able to produce aldosterone

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2
Q

Which hypothalamic hormones affect prolactin release?

A

Dopamine → negative

TRH → positive

NOTE: hypothyroidism causes hyperprolactinaemia (Primary hypothyroidism causes elevated thyrotropin-releasing hormone (TRH) levels that can result in thyrotroph and lactotroph hyperplasia)

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3
Q

How might a pituitary macroadenoma present in women?

A

Amenorrhoea and galactorrhoea

(this is due to compression of the pituitary stalk, reduction in the inhibitory effects of dopamine and increased release of prolactin)

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4
Q

What physical manifestation might a macroadenoma of the pituitary gland (>1cm) cause?

A

Bitemporal hemianopia

NOTE: this can be tested using a visual field test

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5
Q

What is the main problem with prolactinomas?

A

It might reduce/stop the production of other pituitary hormones (e.g. FSH and LH) or affect the axis

High prolactin in itself is not much of an issue.

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6
Q

What is the CPFT?

A

Combined Rapid Anterior Pituitary Evaluation Panel

Test for pituitary function

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7
Q

Which three stimuli of pituitary hormone secretion are used in the CPFT (what drugs are administered)?

A
  • Hypoglycaemia (via insulin) - increases CRH/ACTH and increases GHRH/GH
  • TRH - increases TSH and prolactin
  • LHRH (aka GnRH) - increases LH and FSH
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8
Q

What safety precautions must you take before subjecting a patient to hypoglycaemia?

A
  • No cardiac risk factors (needs a normal ECG)
  • No history of epilepsy
  • Ensure good IV access
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9
Q

Describe the manifestations of increasing hypoglycaemia?

A
  • Initially, the activation of the sympathetic nervous system will result in sweating, tachycardiac etc.
  • When the blood glucose reaches <1.5mM, neuroglycopaenia may occur (loss of consciousness and confusion)
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10
Q

What blood glucose concentration is normally required to stimulate the pituitary gland?

A

<2.2mM

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11
Q

How should a patient be rescued if they experience severe hypoglycaemia during this CPFT?

A

50ml 20% dextrose

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12
Q

How much insulin should a patient be administered to induce hypoglycaemia during a CPFT test?

A

0.15 U/kg

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13
Q

Outline the dosing of various drugs in the CPFT.

A
  • 5mL syringe
  • Insulin (0.15 U/kg)
  • TRH 200 µg
  • LHRH 100 µg

NOTE: the patient may experience a warm flush and vomit when the drug is administered

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14
Q

What should be measured in the blood?

A
  • Glucose
  • Cortisol (caused by insulin)
  • GH (caused by insulin)
  • LH and FSH (caused by GnRH)
  • TSH (caused by TRH)
  • Prolactin (casued by TRH)
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15
Q

How frequently should hormone levels in the blood be measured?

A
  • Every 30 mins for 60 mins - LH, FSH, TSH, prolactin
  • Every 30 mins for 120 mins - glucose, GH, cortisol
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16
Q

Describe the response you would expect from a normal pituitary gland undergoing the CPFT?

A

Blood sugar will go down but then it will rise again without any external help. This is due to production of GH and ACTH (and hence cortisol) in response to the metabolic stress.

17
Q

What should be done if a response isn’t observed at a plasma glucose of 2.2 mM?

A

Give more insulin

18
Q

What level of cortisol and GH is considered a normal response?

A

Cortisol >550nM

GH >10 IU/L

19
Q

List the order of hormone replacement in someone with panhypopituitarism.

A
  • Hydrocortisone
  • Thyroxine
  • Oestrogen
  • GH

NOTE: Fludrocortisone is not necessary because the adrenals can still produce aldosterone

20
Q

How should a patient with a prolactinoma be treated?

A

Dopamine agonists (e.g. cabergoline)

This reduces the size of the tumour and can avoid surgery

21
Q

What is disconnection hyperprolactinaemia?

A

Compression of the pituitary stalk by a tumour cuts off the negative effect of dopamine on pituitary prolactin secretion

This results in hyperprolactinaemia

22
Q

Why do non-functioning adenomas need surgery?

A

They do NOT respond to dopamine agonists

23
Q

Why might prednisolone replace hydrocortisone as the first-line steroid replacement agent?

A

It has a longer half-life meaning that once daily dosing is possible

24
Q

How should you investigate a child with poor growth who is suspected of having a GH deficiency?

A
  • Take a random plasma GH measurement (GH is pulsatile but if you happen to measure it during a pulse and they have detectable GH then it shows that they are produing GH)
  • Excercise test
  • Insulin tolerance test (effective but dangerous so should NOT be done straight away)
25
Q

Name two tests that may be used to investigate suspected acromegaly.

A
  • Oral glucose tolerance test
  • IGF-1 levels

NOTE: the normal ranges for IGF-1 are not fuly resolved and they vary with age

26
Q

What are the management options for acromegaly

A
  1. Pituitary Surgery
  2. Others
    1. Pit radiotherapy
    2. Cabergoline
    3. Ocreotide