pituitary Flashcards
diabetes insipidus
a lack of diuretic hormone (ADH) or lack of response to ADH
–> prevent kidneys from being able to concentrate urine leading to polyuria + polydipsia
types of diabetes insipidus
nephrogenic - collecting ducts of kidneys do not respond to ADH
cranial - hypothalamus does not produce ADH for the pituitary gland to secret
causes of nephrogenic diabete insipidus
drugs - lithium (used in bipolar affective disorder)
intrinsic kidney disease
electrolyte disturbance - hypOkalaemia + hypercalcaemia
mutation in what gene can cause nephrogenic diabetes?
AVPR2 gene on X chromosome that codes for ADH receptor
presentation of diabetes insipidus
polyuria + polydipsia
dehydration
postural hypotension
hypernatremia
what is the water deprivation test (desmopressin stimulation test) ? what is it used to diagnose?
diabetes insipidus / primary polydipsia
patient avoids fluid for 8hrs, urine osmolality measured synthetic ADH (desmopressin) is given 8hrs later urine osmolality measured again
(different results for each nephrogenic, cranial + primary polydipsia)
diabetes insipidus management
treat underlying cause, if mild manage conservatively
demopressin (synthetic ADH) - for both, higher dose in nephrogenic (monitor closely)
dibetes insipidus investigations
low urine osmolality
high serum osmolality
water deprivation test = test of choice
water deprivation test urine osmolality results in cranial diabetes insipidus
after deprivation = low
after ADH = high
water deprivation test urine osmolality results in nephrogenic diabetes insipidus
after deprivation = low
after ADH = low
water deprivation test urine osmolality results in primary polydipsia
after deprivation + after ADH given both = high
primary polydipsia = when the patient has a normally functioning ADH system but they are drinking excessive quantities of water leading to excessive urine production. They don’t have diabetes insipidus.
what is hypopituitarism physiologically due to?
inability of pituitary gland to provide sufficient hormones due to -
- inability of pituitary to produce hormones
- insufficent supply of hypothalamic-releasing hormones
causes of hypopituitarism
pituitary tumours
local brain tumours - meningioma, glioma, craniopharyngiomas
infiltrative processes - sarcoidosis
infections - cerebral abscesses, meningitis
trauma - head injury
autoimmune
iatrogenic/surgery
hypopituitarism presentation
huge spectrum - depends on severity, hormones predominantly involved
mentrual irregularities gynaecomastia in males abdominal obesity loss of facial, axillary or pubic hair dry skin + hair growth retardation
risk of testosterone replacement
polycythaemia = high conc of RBCs in blood
–> risk of stroke/MI, monitor
prostate enlargement - not cancer
hepatitis
what is cushing’s syndrome?
prolonged elevation of cortisol
causes protein loss
whats the difference between cushing syndrome + cushing disease?
syndrome = prolonged elevation of cortisol
disease = where pituitary adenoma secretes excessive ACTH
disease causes syndrome but sundrome not always caused by disease
causes of cushing syndrome
long term steroid use
pituitary adenoma secreting excessive ACTH (cushings disease)
adrenal adenoma (hormone secreting adrenal tumour)
paraneoplastic - ectopic ACTH (small cell lung cancer)
presentation of cushings syndrome
round moon face central obesity thin, weak limbs abdominal striae buffalo hump - fat pad on back frontal balding in women conjunctival oedema (chemosis)
osteoporosis
easy brusing + poor skin healing
high stress hormone levels
- hypertension
- cardiac hypertrophy
- hyperglycaemia - T2DM
- depression
- insomnia
cushings syndrome investigations
dexamethsone suppression test - overnight or over couple days, positive if cortisol not suppressed
24hr free cortisol
MRI of brain - pituitary adenoma
chest CT - small cell lung cancer
abdo CT - adrenal tumours
management of cushing syndrome
remove underlying cause - ectopic, transphenoidal for pituitary tumour
if fails reove but adrenal glands + give replacement steroid hormone for life
metryapone
pharmacological management of cushings syndrome
metryrapone - if others fail or while waiting for radiotherapy to work
what does a pituitary adenoma releasing excessive ACTH cause?
Cushings disease –> cushing syndrome - prolonged elevation of cortisol
presentation of prolactinoma
female
- EARLY presentation
- galactorrhoea (milky nipple discharge)
- menstrual irregularity
- amenorrhoea (lack of periods)
- infertility
male
- LATE presentation
- impotence
- abnormal visual field
- anterior pituitary malfunction
prolactinoma investigations
wraised serum prolactin
MRI of pituitary
check visual field
pituitary function tests - other hormones affected
pathological causes of raised prolactin
hypothyroidism
stalk lesions - iatrogenic, road accident
prolactinoma (prolactin secreting tumour)
drugs that increase prolactin
drugs that inhibit dopamine (antagonists) - antiemetics (metoclopramide)
antipsychotics
antidepressants
physiological causes of a raised prolactin
breast feeding
pregnancy
stress
lack of sleep
management of prolactinomas
dopamine agonists = cabergoline (dostinex)
- 1/2 times a week oral
others = bromociptine, quinagolide
v successful - tumour shrinkage, pregnancy/menstruation, normal prolactin
side effects of dopamine agonists
N+V
low mood
fibrosis (in high doses)
cause of acromegaly
excessive growth hormone
commonest cause = pituitary adenoma
can be secondary to lung/pancreatic cancer that secretes ectopic growth hormone releasing hormone (GHrH) or GH (rare)
acromegaly presentation
prominent forehead + brow large nose, tongue, jaw headaches - vascular skin tags profuse sweating
bitemporal hemianopia arthritis - imbalanced growth of joints hypertrophic heart hypertension T2DM
what conditions does acromegaly increase the risk of?
colorectal cancer - colonic polyps
early CV death
acromegaly investigations
insulin-like growth factor (IGF-1) - raised
OGTT while measuring GH (high glucose usually suppresses growth hormone)
MRI brain - pit tumour
ophthalmology - visual field testing
check other pit hormones
*random GH level not useful - fluctuates
management of acromegaly
surgery = definitive, remove source
pharmalogical
- somatostatin analogues - ocreotide
- dopamine agonists - bromocriptine
- pegvisomant
- somatostatin + dopamine has inhibitory effect on GH release
- somatostatin = more potent
somatostatin analogues
ex = ocreotide
blocks GH release - acromegaly treatment
– shrinks tumour in most, used pre-op
SE = abdo pain, diarrhoea, gall stones
what inhibits growth hormone release?
somatostatin + dopamine
causes of SIADH
post-operative
infection - atypical pneumonia, lung abscesses
head injury
medications - thiazide diuretics, carbamazepine, antipsychotics, NSAIDs
malignancy - small cell lung cancer
meningitis
medication that can cause SIADH
thiazide diuretics carbamazepine antipsychotics NSAIDs sulfonylureas SSRIs
Anti-diuretic hormone (ADH) function
produced in the hypothalamus + secrete in the posterior gland of the pituitary
ADH stimulates water reabsorption from collecting ducts in the kidneys
also know as vasopressin
pathophysio of SIADH
excessive ADH results in excessive water reabsorption in the collecting ducts
–> this water dilutes the sodium in the blood = hyponatraemia
(reabsorption not big enough to cause fluid overload = euvolemia hyponatraemia)
urine becomes more concentrated - urine osmalality + urine sodium high
syndrome of inappropriate diuretic hormone presentation
severe hypOnatraemia
- seizures
- reduced consciousness
non-specific
- headache, fatigue
- muscle aches + cramps
- confusion
SIADH investigations
hyponatraemia
high urine sodium
high urine osmolality
euvolemia
exclude other causes of hyponatraemia
establish cause - chest x-ray
SIADH managment
correct sodium - SLOW, prevent central pontine myelinolysis
fluid restriction might be enough to correct
tolvaptan (‘vaptans’) = ADH receptor blockers
demeclocycline (tetracycline antibiotic) = inhibits ADH
complication of SIADH
central pontine myelinolysis (osmotic demylination)
–> long term hyponatraemia being treated too quickly
osmosis causes brain to swell
