- NDI should be differentiated from central diabetes insipidus (CDI)
and psychogenic polydepsia. Both NDI and CDI could be complete or
partial syndrome.
The three conditions could be differentiated by water deprivation test
which aims to increase plasma osmolality to 295 mosmol/kg by water
deprivation (alternatively by giving hypertonic saline 5% Nacl in a
dose of 0.05 ml/kg/min for 2 hours) then looking for urine volume and
urine osmolarity.- Normally, as plasma osmolarity increases to 295 mosmol/kg, the
urine volume will decrease and urine osmolality will increase to
800-1400 mosmol/kg. - In psychogenic polydepsia, urine volume will gradually decrease
and urine osmolality will increase up to 800 mosmol/kg. - In complete NDI or CDI the urine volume and osmolarity will not
change (even the patient may become shocked from hypovolaemia
so blood pressure should be watched hourly and body weight
should not be allowed to decrease by more than 3-5%).
When plasma osmolality reaches 295 mosmol/kg or hypotension
occurs, ADH is given in the form of DDVAP intranasally or 5 units
of aqueous vasopressin i.v. Urine volume will decrease and
osmolality will increase up to 800 in CDI but no change will occur
in NDI.
In partial syndrome (NDI or CDI) water deprivation will increase
osmolality to 400-500 mosmol/kg and some decrease in urine
volume occurs. On giving vasopressin or DDVAP, urine
osmolarity will increase to 800 in CDI and not in NDI.
- Normally, as plasma osmolarity increases to 295 mosmol/kg, the
Treatment:
- Treatment of the cause.