8. Pituitary disorders Flashcards
What is the most common cause of pituitary malfunction?
benign tumour (adenoma)
Are pituitary tumours usually ‘functional’ or ‘non-functioning’? What is the difference?
- most are non-functioning: don’t produce hormone themselves but can cause hypopituitarism (underproduction) due to physical pressure from growing tumour on glandular tissue
- functional tumours are rarer: can cause hyperpituitarism (overproduction)
What are the symptoms of pituitary adenomas? Explain why these occur.
pressure on surrounding structures causes:
- headache
- visual problems
- eye mov. probs.
- vomiting and nausea
- symptoms associated with either underproduction (non-functioning) or overproduction (functional) of pituitary hormones
Which 3 investigations are performed when a pituitary tumour is suspected?
i. MRI scan: delineation of anatomy, size and topographical location of pituitary or parapituitary mass
ii. assessment of visual field defects
iii. assessment of endocrine function to determine any hormonal excess/deficiency:
- measuring hormone levels in blood
- staining sections from a biopsy of the tumour with antibodies for the relevant hormone
Which symptoms indicate lateral or superior growth of tumour?
lateral growth:
- headaches (compression of nerves Va and Vb)
- eye mov. probs. (compression of nerves III, IV or VI)
superior growth:
- visual probs. (compression of optic nerve)
What are the possible causes of hypopituitarism? Which is most common?
Most common:
1. pituitary adenoma (mass effects)
Rarer causes:
- radiation therapy
- inflammatory disease
- head injury
Which hormones are lost first in hypopituitarism?
typically a progressive loss of AP function with GH and FSH/LH 1st to be affected
Which term is used to describe deficiency of all AP hormones?
panhypopituitarism
In which cases would secretion of ADH and oxytocin from PP be affected?
- if tumour affects hypothalamic function
2. if inflammatory process is involved
What are the typical causes of GH deficiency in adults or children?
adults: mass effects from pituitary adenoma
children: usually idiopathic but can involve specific gene mutations and autoimmune inflammation
What are the symptoms of GH deficiency in adults?
often quite subtle:
- decreased exercise tolerance
- decreased muscle strength
- increased body fat
- reduced sense of “well-being”
What are the effects of prenatal GH deficiency?
usually has little effect on foetal growth
if severe can cause hypoglycaemia and jaundice
What are the effects of GH deficiency in childhood?
poor growth and short stature
What is the treatment for GH deficiency?
recombinant GH
What are the symptoms of gonadotropin deficiency from a pituitary adenoma?
women:
- lack of libido
- infertility
- oligoamenorrhea/amenorrhea
men:
- lack of libido
- impotence
What is diabetes insipidus?
ADH deficiency
What are the possible causes of ADH deficiency?
- hypothalamic tumour
- pituitary tumour that has extended into hypothalamus
- cranial radiotherapy
- pituitary surgery
- autoimmune infiltration
- infections such as meningitis
What are the 2 main effects of ADH deficiency?
- excess secretion of dilute urine… dehydration
2. increased sensation of thirst (polydipsia)
What are the 3 main conditions caused by a hypersecreting pituitary adenoma?
- prolactin excess
- GH excess: gigantism or acromegaly
- ACTH excess: Cushing’s syndrome
How is prolactin secretion by AP lactotropes regulated?
i) PRH stimulates secretion
ii) PIH (dopamine) inhibits secretion - dominates
What are the symptoms of hyperprolactinaemia?
- galactorrhea (unexplained milk production, rare in men)
- gynecomastia (hard breast tissue)
- hypogonadism (diminished activity of testes/ovaries)
- amenorrhea
- erectile dysfunction
Why is hypogonadism a symptom of hyperprolactinaemia?
increased plasma prolactin… increased dopamine due to neg. feedback… decreased GnRH… decreased FSH/LH
Name 4 possible causes for hyperprolactinaemia.
- hypersecreting pituitary adenoma (prolactinoma) - most common cause
- non-functioning pituitary adenoma (‘stalk effect’)
- physiological causes: pregnancy, suckling, stress and exercise
- dopamine antagonist drugs, inc. antipsychotics (e.g. haloperidol) and antidepressants (e.g. clomipramine)
How can one differentiate between a prolactinoma and a non-functioning pituitary adenoma?
- hypersecreting prolactinoma: prolactin >5000 mU/L
- non-functioning adenoma: prolactin <5000 mU/L
What is the treatment for prolactinoma and a non-functioning pituitary adenoma?
- prolactinoma: dopamine R agonists, e.g. cabergoline
- non-functioning pituitary adenoma: trans-phenoidal surgery (or radiotherapy)
What is acromegaly and which is diagnosis often late?
- GH excess caused by hypersecreting pituitary adenoma (typically large so also associated with local mass effects)
- effects of increased GH and IGF-1 receptor activation often take several years to manifest as change in physical appearance
What are the symptoms of acromegaly?
gradual change in physical features:
- broad nose, coarse facial features, thick lips and prominent supraorbital ridge
- enlargement of hands and feet
- excessive sweating and greasy skin
local mass effects:
- headaches
- visual field defects
- other cranial nerve palsies
Which condition is caused by excess GH secretion in childhood?
gigantism
What are the long-term complications of GH excess if untreated?
- diabetes mellitus and hypertension (as GH antagonises the actions of insulin)
- some forms of cancer, e.g. colon or thyroid (due to increased IGF-1)
- irreversible body changes
- premature cardiovascular death
Which biochemical tests are used to diagnose acromegaly?
- oral glucose tolerance test: failure to suppress GH <1ug/L
- elevated IGF-1 level
- GH day curve: elevated mean GH
What are the treatment options for agromegaly?
- trans-sphenoidal surgery
- radiotherapy: external beam (multiple short bursts over several wks) or gamma knife (high conc. over single time)
- drug therapy
Which drugs can be used to treat acromegaly?
- GH R antagonists, eg pegvisomant
- dopamine R agonists, eg cabergoline - some efficacy in decreasing GH (but much higher dose than for prolactinoma)
- synthetic somatostatin analogs, eg octerotide
