2. Hypersecretion of anterior pituitary hormones Flashcards
what can hypersecretion of the anterior pituitary be due to?
- isolated pituitary tumours
- can also be ectopic (from non-endocrine tissue e.g. neuroendocrine tumours)
what is hypersecretion of the anterior pituitary often associated with?
often associated with visual field and other defects (e.g. cranial nerves)
what does an absence of black in an MRI scan mean?
absence of CSF
what is bitemporal hemianopia?
tunnel vision
what is bitemporal hemianopia caused by?
compression of the fibres from the nasal retinae that cross at the optic chiasm, leading to loss of vision from the outer temporal visual fields
what might compress fibres at the optic chiasm?
suprasella tumour
how can visual fields be examined?
perimetry
what does excess ACTH (corticotrophin) result in?
cushing’s disease (if due to anterior pituitary tumour)
what does excess TSH (thyrotrophin) result in?
thyrotoxicosis - high TSH and high T4
what does excess gonadotrophins (LH,FSH) result in?
early puberty in children
what does excess prolactin result in?
hyperprolactinaemia
what does excess GH result in?
gigantism (in children) and acromegaly (in adults)
in which situations is it physiological to have high prolactin?
pregnancy and breastfeeding
what do you get at the end of pregnancy to prepare for breastfeeding?
lactotroph hyperplasia
what are the pathological causes of hyperprolactinaemia?
prolactinoma (often a microadenoma so <10mm in diameter)
what effect does high prolactin have on LH and FSH production?
suppresses GnRH pulsatility -> less GnRH -> less LH and FSH production
what does hyperprolactinaemia due to prolactinoma cause in women and men?
women: glactorrhoea (milk production), secondary amenorrhoea (or oligomenorrhoea) due to decreased LH and FSH, loss of libido, infertility
men: loss of libido, erectile dysfunction, infertility
how is prolactin secretion regulated?
dopamine released from hypothalamic dopaminergic neurones bind to D2 receptors all over the lactotroph to inhibit prolactin
how can hyperprolactinaemia be treated?
- dopamine receptor (D2) agonist (tablets) e.g. cabergoline and bromocriptine
- tumour may need to be surgically removed if it is large
why is cabergoline preferred over bromocriptine as a dopamine receptor agonist?
- more effective
- needs to be taken 1/2 times a week rather than daily
what are the side effects of dopamine receptor agonists?
- nausea and vomiting
- postural hypotension (dizziness)
- dyskinesia
- depression/anxiety
- pathological gambling
what is gigantism and what are its effects?
XS GH in children -> growth doesn’t stop and you keep on growing linearly
people with gigantism can die from infection because too much GH is not good for you
what is acromegaly and what are its effects?
XS GH in adults -> increase in soft tissue growth and cartilage growth
can result in cardiovascular disease (predisposition to higher BP, glucose intolerance and diabetes), respiratory complications (soft tissue grows around neck/palate) and cancer (lots of GH causes malignancy)
what grows in acromegaly?
- periosteal bone
- cartilage
- fibrous tissue
- connective tissue
- internal organs
what are the clinical features of acromegaly?
- excessive sweating
- headache
- enlargement of supraorbital ridges, nose, hands and feet
- thickening of lips and coarseness of features
- enlarged tongue (macroglossia)
- protrusion of lower jaw
- carpal tunnel syndrome (median nerve compression due to tissue growth in wrist)
- barrel chest
what are the metabolic effects of acromegaly?
excess GH -> increased glucose production -> decreased muscle glucose uptake -> increased insulin production -> increased insulin resistance -> impaired glucose tolerance -> diabetes
what are complications of acromegaly?
- obstructive sleep apnoea: narrowing of upper airway and possible collapse due to tissue growth
- hypertension: GH/IGF-1 effects directly, GH mediated renal sodium reabsorption
- cardiomyopathy: hypertension, DM
- increased risk of cancer: colonic polyps
how can acromegaly be diagnosed?
IGF-1 is not pulsatile so elevated IGF-1 serum
oral glucose test: paradoxical risk of GH following oral glucose load
what are the treatments of acromegaly?
- surgery to remove tumour
- somatostatin analogues (e.g. octreotide) and dopamine agonists (e.g. cabergoline)
- radiotherapy
how are somatostatin analogues used to treat acromegaly?
short lasting injection/monthly depot which reduce GH secretion dramatically and shrink the tumour
when may somatostatin analogues be used?
pre-treatment: to make surgery easier
post-operatively: if not cured or waiting for radiotherapy to take effect
what are the common GI side effects of somatostatin analogues?
nausea, diarrhoea, gallstones
this is because it is an ‘endocrine cyanide’ which inhibits lots of peptides, not just GH
