diabetes insipidus Flashcards
what is diabetes insipidus and what is the cause?
It is caused by vasopressin/ADH deficiency (cranial DI) or vasopressin/ADH resistance, leading to passing large volumes of dilute urine with polydipsia
what are the biochemical hallmarks of DI?
- high serum osmolality
- low urine osmolality
- high urine volume
what is cranial DI?
seen in pituitary disease
strong family history of CDI suggests a genetic cause
what is nephrogenic DI?
caused by metabolic and electrolyte disturbance, renal disease, and drugs affecting the kidney
what is primary polydipsia?
a form of polydipsia characterised by excessive fluid intake in the absence of physiological stimuli to drink.
a behavioural condition, leading to polydipsia, which drives polyuria.
may lead to dilution hyponcatreaemia
why can it be hard to distinguish primary polydipsia from partial DI?
Some patients with primary polydipsia have an impaired ability to concentrate urine due to down-regulation of vasopressin release, and this can occasionally make it difficult
what investigations are done to confirm DI?
when urine volume >3L per 24hrs, with high serum osmolality and low urine osmolality
if serum osmolality is >295
urine osmolality <300
what is the water deprivation test and what can the results indicate ?
patient empties bladder and is weighed and serum osmolality is taken. then no fluid for 8 hrs.
may be useful in partial DI.
patients with frank DI will have unacceptable thirst and lose weight due to water loss
stop if weight loss is too excessive and symptoms are severe
in the second part of the test, syntheticc vasopressin (DDAVP) is given. In cranial DI, DDAVP leads to reduced urine volume and increase urine osmolality
in nephrogenic DI there is no response
if DI is clinically obvious, there is no need to do test
what urine osmolality rules out DI?
> 600
how should cranial DI be managed?
- investigate for pituitary disease and manage appropriately
- responds well to synthetic vasopressin (DDAVP)
- desmopressin may be given intra nasally, orally, sublingually or parenterally
what are the signs of DDAVP over treatment and what can it cause?
DDAVP treatment is in cranial DI
over treatment with DDAVP may lead to dilution hyponatreamia, characterised by headache and reduced cognitive ability, and less commonly seizures if there is a sudden NA drop
what are the sings of DDAVP under treatment in cranial DI?
excessive thirst
polyuria
what is hypodipsic DI?
if there is an impaired thirst mechanism in patients with DI if there is hypothalamic involvement
may be seen in hypothalamic infiltrative disorders and requires specialist care because of risk of hypernatreamia and dehydration
how is nephrogenic DI treated?
treat underlying cause and reverse
if symptoms persist
- drink according to thirst and keep up with water loss
specific measures include
- low salt and protein diet
- diuretics
- NSAIDS
