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Central Diabetes Insipidus (Symptoms (Aetiology (Disease of the…
Central Diabetes Insipidus
Symptoms
Aetiology
Disease of the hypothalamus
Tumour
Congenital defects in ADH gene
Trauma
Idiopathic
Infiltrative disease
Polyuria - 15L in 24 hours
Compensatory polydipsia - thirsty
NO GLYCOSURIA
Hypernatraemia due to water loss in EXCESS of Na loss (Na becomes more concentrated)
Can lead to dehydration which can be severe if the thirst mechanism or consciousness is impaired or the patient is denied fluid
Pathophysiology
The passage of large volumes (>3L/day) of dilute urine due to impaired water reabsorption in the kidney either because of:
Reduced ADH secretion from the posterior pituitary
Treatment Plan
Find the cause
MRI of head and test anterior pituitary (looking for tumour that could affect posterior pituitary)
Give synthetic analogue of ADH e.g. oral Desmopressin
Has a long duration of action and has no vasoconstrictive effects
Investigations
Urine volume measured to confirm polyuria - DI is unlikely if urine volume < 3L/day
Check blood glucose to exclude diabetes mellitus
Water deprivation test
Aims to determine whether kidneys continue to produce dilute urine despite dehydration
To differentiate between cranial and nephrogenic - use Desmopressin
Urine won't be concentrated in nephrogenic DI but will in cranial DI when desmopresin is used
MRI of hypothalamus - to look for masses (useful for cranial DI diagnosis