D&E - Pituitary Disorders

Question 1

What are the causes of prolactinaemia?

Answer 1

• pregnancy
• medications (e.g. anti-emetics, antipsychotics)
• hypothyroidism
• PCOS
• prolactinoma

Question 2

What are micro-prolactinomas?

Answer 2

The commonest pituitary tumour, presenting with menstrual disturbances, hypogonadism and galctorrhoea.

Infertility may be a feature.

Micro-prolactinomas are <1cm.

Question 3

What are macro-prolactinomas?

Answer 3

Large pituitary adenomas (>1cm), causing extremes in serum prolactin levels.

Question 4

How are prolactinomas treated?

Answer 4

Dopamine receptor agonists suppress prolactin secretion from the pituitary gland.

Even large macro-prolactinomas are medically treated.

Question 5

Describe the growth hormone axis.

Answer 5

1. Hypothalamus produces GHRH
2. GHRH stimulates release of GH from anterior pituitary gland
3. GH stimulates the release of IGF-1 from the liver

Question 6

What are the actions of growth hormone?

Answer 6

• stimulates muscle growth
• increases bone density and strength
• stimulates cell regeneration and reproduction
• stimulates growth of internal organs

Question 7

What is acromegaly?

Answer 7

A condition that is as a result of excess growth hormone.

Question 8

What are the causes of excess growth hormone?

Answer 8

• pituitary adenoma
• paraneoplastic ectopic GHRH or GH secretion

Question 9

Presentation of acromegaly.

Answer 9

• frontal bossing
• coarse, sweaty skin
• large nose
• macroglossia
• large hands and feet
• large protruding jaw

Question 10

Which other medical conditions may have acromegaly as an underlying cause?

Answer 10

• hypertrophic heart
• hypertension
• T2DM
• carpal tunnel syndrome (esp. bilaterally)
• arthritis
• colorectal cancer

Question 11

How does a space occupying pituitary tumour present?

Answer 11

• headaches
• visual field defect (bitemporal hemianopia)

Question 12

Investigations for acromegaly.

Answer 12

IGF-1 on blood sample (cannot test GH as fluctuates too much).

Growth hormone suppression test - consume 75g glucose drink with growth hormone tested at baseline and 2 hours following the drink. Glucose should suppress the growth hormone level in healthy individuals.

MRI of the pituitary to diagnose a pituitary adenoma.

Question 13

What is the treatment of acromegaly?

Answer 13

Trans-sphenoidsal surgery to remove a pituitary adenoma if this is the cause.

Medical options include:
- pegvisomant
- somatostatin analogues
- dopamine agonists

Question 14

What are non-functioning pituitary adenomas?

Answer 14

Biochemically inactive tumours of the pituitary gland, which can be removed surgically if there is a visual field defect or there is a threat to vision.

Question 15

What is the pathophysiology of syndrome of inappropriate ADH (SIADH)?

Answer 15

Excessive ADH results in increased water reabsorption in the collecting ducts, causing a euvolaemic hyponatraemia.

Question 16

Presentation of SIADH?

Answer 16

• headache
• fatigue
• muscle aches / cramps
• confusion

Question 17

What are the causes of SIADH?

Answer 17

• post-operative
• SSRIs
• small cell lung cancer

Question 18

What are the clinical features of SIADH?

Answer 18

• euvolaemia
• hyponatraemia
• low serum osmolality
• high urine sodium
• high urine osmolality

NOTE SIADH can only be diagnosed after the exclusion of hypothyroidism, total salt depletion and ACTH deficiency.

Question 19

How should SIADH be managed?

Answer 19

• admission if severe or symptomatic hyponatraemia
• treat the underlying cause
• fluid restriction
• vasopressin receptor antagonists to block ADH receptors

Question 20

What is the major complication of treating SIADH quickly?

Answer 20

Osmotic demyelination syndrome.

As blood sodium concentration falls, water moves via osmosis across the BBB into the brain, causing the brain to swell.

The brain adapts to this by reducing the solutes in the brain cells, so that it does not become oedematous. If hyponatraemia has been present, the brain cells therefore have low osmolality.

When sodium levels rise rapidly during treatment, demyelination of the pons causes cognitive and behavioural changes, and carries a significant risk of death.

Question 21

What is:

a) cranial diabetes insipidus?

b) nephrogenic diabetes insipidus?

Answer 21

The kidneys are unable to reabsorb water and concentrate urine due to:

a) lack of ADH

b) lack of response to ADH

Question 22

What are the causes of nephrogenic diabetes insipidus?

Answer 22

• medications (lithium)
• genetic mutations in ADH receptor gene
• hypercalcaemia
• hypokalaemia
• PCKD

Question 23

What are the causes of cranial diabetes insipidus?

Answer 23

• brain tumours
• brain injury
• brain infections
• genetic mutations in the ADH gene

Question 24

Presentation of diabetes insipidus.

Answer 24

• polyuria
• polydipsia
• dehydration
• postural hypotension

Question 25

How is diabetes insipidus investigated?

Answer 25

• low urine osmolality
• high serum osmolality
• ≥3L/24hr on catheter

Question 26

How is diabetes insipidus diagnosed?

Answer 26

Water deprivation test.

Question 27

Describe how the water deprivation test is performed and interpreted.

Answer 27

Patient avoids fluids for 8 hours before the test, and urine osmolality is measured. If osmolality is low, synthetic ADH is given. Urine osmolality is measured again in 2-4 hours.

In primary polydipsia, water deprivation will cause urine osmolality to be high when first measured, ruling out diabetes insipidus.

If urine osmolality is low, desmopressin is given. If urine osmolality rises, this is cranial diabetes inspidus. If it doesn’t, this is nephrogenic diabetes insipidus.

Question 28

How is cranial diabetes insipidus managed?

Answer 28

Desmopressin (synthetic ADH) to replace absent ADH.

Question 29

How is nephrogenic diabetes insipidus managed?

Answer 29

• access to plenty of water
• high dose desmopressin
• thiazide like diuretics
• NSAIDs