Posterior pituitary - DI and SIADH Flashcards
Where are the hypothalamic osmoreceptors located?
Organosum vasculosum
To where do the osmoreceptors project?
PVN and SON
What are the target cells for VP?
Renal collecting duct cells
Differentiate between cranial and nephrogenic DI
Cranial = lack/absence of VP production Nephrogenic = CD cells unresponsive to VP
List 5 possible causes of cranial DI
- TBI
- Pituitary tumour (craniopharyngoma)
- Granulomatous inflammation of median eminence + pituitary stalk (TB, sarcoidosis)
- metastasis
- pituitary surgery
Recall 2 possible causes of nephrogenic DI
- Congenital (V2/AQP mutation)
2. Ingestion of Lithium for psychiatric disorders (eg bipolar)
What are the 3 key clinical features of DI?
Polyuria
Polydipsia
Hypo-osmolar urine
What is the most likely cause of psychogenic polydipsia?
Anti-cholinergic drugs give a ‘dry mouth’
How does plasma osmolality differ between DI and PP?
DI = 290 PP = 270
How do the biochemical features of DI and PP differ?
DI - HYPERnatraemia, INCREASED plasma osmolality
PP - mild HYPOnatraemia, LOW plasma osmolality
What test and measurements are performed to make a diagnosis of CDI, NDI or PP?
Water deprivation:
Measure:
1. weight (to prevent severe dehydration)
2. Urine osmolality (remains low in DI, higher in PP)
3. urine osmolality after DDAVP given (remains low in NDI, increases in CDI)
How is cranial DI treated and what methods of administration can be used?
DDAVP (desmopressin) = V2 receptor agonist
Nasally
Orally
Subcutaneously
How is nephrogenic DI treated?
Thiazide antidiuretics
What is SIADH?
Inapropriately high ADH for current plasma osmolality
Recall the pathophysiology of SIADH
- VP high
- More water reabsorbed
- ECF expands
- Hyponatraemia, ANP released
- ANP –> natiuresis
- Natiuresis exacerbates hyponatremia
- Euvolaemia
