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Summary Endocrinology dynamic testing
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These files contains dynamic testing for endocrinology diseases.
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A 42-year-old man undergoes trans- DIABETES INSIPIDUSsphenoidal surgery for a large, non- Decreased secretion of antidiuretic hormone from the
pituitary or insensitivity to antidiuretic hormone
functioning pituitary macro-adenoma. CENTRAL: caused by reduced secretion of ADH. Idiopathic,
Preoperatively, dynamic pituitary hormone autoimmune, neurosurgery, trauma, familial (e.g., Wolfram’s),
tests were normal, as was his fluid intake CDI, infection (TB, abscess), tumour (craniopharyngioma,
leukaemia), infiltrative (sarcoidosis), post-radiotherapy
and output. Two days following surgery he NEPHROGENIC: caused by resistance to the effect of ADH.
developed acute polyuria, extreme thirst, AVPR2 mutation, Aquaporin 2 mutation, lithium, electrolyte
(hypercalcaemia, hypokalaemia), demeclocycline, sickle-cell,
and polydipsia. His urine output over the pyelonephritis
next 24 hours was 6 litres, with frequent CLINICAL FEATURES: polyuria, polydipsia, nocturia
nocturia. What is the likely diagnosis? INVESTIGATIONS: high plasma osmolality, low urine
osmolality, water deprivation test/ desmopressin stimulation
test
MANAGEMENT: CENTRAL (synthetic ADH, desmopressin –
SE: water retention, hyponatremia), NEPHROGENIC (correct
underlying cause, thiazides, low salt/ protein diet). Thiazide to
cause prompt hypovolaemia -> increased sodium and water
reabsorption
A 76-year-old homeless white man presents SIADH
to the emergency department after police PATHOPHYS: In SIADH abnormal release results in kidneys
retaining more water -> Increase in total body water ->
find him disoriented on the streets. The dilutional hyponatraemia. SIADH results in hypotonic
patient gives little history, but admits to hyponatremia, concentrated urine, euvolemic state
ongoing cough with productive sputum, AETIOLOGY: CNS (stroke, SAH, trauma), neoplasia (SCLC,
neuroblastoma), infective (pneumonia, HIV), drugs
night sweats/chills, and mild dyspnoea. He (carbamazepine, SSRI, MDMA), hypothyroid, hypopituitarism,
proceeds to suffer from a seizure. Vital signs surgery
CLINICAL FEATURES: headache, confusion, lethargy,
demonstrate an elevated temperature, anorexia, mod-severe (seizures, reduced GCS, coma,
increased RR, 94% oxygen saturation (on 3 L myoclonus, ataxia, hyporeflexia, asterixis)
of O2), and pulse 87 bpm. Physical INVESTIGATIONS: renal function (hyponatraemia), low
serum osmolality, high urine osmolality
examination demonstrates a malnourished MANAGEMENT: mild (no specific treatment, treat underlying
and dishevelled man in a postictal state. cause), more severe: fluid restriction (500-1000mL/24hrs, CI
in SAH cause); pharmacological (vaptans- vasopressin
There is no sign of injury to the body. receptor antagonist); severe hyponatraemia (intensive care,
Crackles can be heard at the right lung base. hypertonic saline, furosemide); long term (self-limiting,
What is the likely diagnosis? reversible, if persistent, fluid restriction and oral salt)
OSMOTIC DEMYELINATION SYNDROME: cerebral pontine
myelinosis, caused by rapid correction of hyponatremia, due
to rapid increase in extracellular osmolality, can cause
irreversible neurological damage
ASSESS FOR: diabetes insipidus
PHYSIOLOGY: pt subjected to dehydration which
normally stimulates the posterior pituitary to release
ADH resulting in increased water retention in the
kidneys and therefore concentrated urine
PROCEDURE: pt avoid taking fluids for 8 hours (fluid
WATER DEPRIVATION TEST deprivation) -> urine sent for urine osmolality and
blood sent for serum osmolality -> view results after 8
hours -> if normal (urine osmolality >750nmol/kg),
stop test, if abnormal, give 2mcg of desmopressin and
continue ->if urine osmolality >750nmol/kg, indicates
cranial DI, if urine osmolality <750nmol/kg, indicated
nephrogenic DI as kidneys resistant to ADH
INSULIN STRESS TEST ASSESS FOR: GH and/or cortisol deficiency (in patients with
pituitary/ hypothalamic disease), gold standard fo pituitary
function
PHYSIOLOGY: insulin used to induce extreme
hypoglycaemia, during which GH and ACTH should be
released as part of the stress mechanism
CI: IHD, epilepsy, previous MI, pregnancy
PROCEDURE: ensure medication available if hypo occurs and
ensure ECG done. Pt should lie supine, take basal cortisol GH
and glucose levels, give Actrapid insulin IV -> check CBG
every 15 minutes -> if CBG not <2.2 mmol/L in first 45 minds,
give another ½ dose of insulin -> once CBG <2.2 mmol/L,
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