Diabetes insipidus Flashcards
define diabetes insipidus?
a disorder of inadequate secretion of antidiuretic hormone or an insensitivity to antidiuretic hormone
what are the two types of DI?
- Cranial DI: failure of ADH secretion by the posterior pituitary
- Nephrogenic DI: insensitivity of the collecting duct to ADH
what are the causes of cranial DI?
- Idiopathic
- Tumours (e.g. pituitary tumour)
- Infiltrative (e.g. sarcoidosis)
- Infection (e.g. meningitis)
- Vascular (e.g. aneurysms, Sheehan syndrome)
- Trauma (e.g. head injury, neurosurgery)
- Haemochromatosis
what are causes of nephrogenic DI?
- Idiopathic
- Drugs (e.g. lithium)
- Post-obstructive uropathy
- Pyelonephritis
- Pregnancy
- Osmotic diuresis (e.g. diabetes mellitus)
what is the epidemiology of DI?
• Median onset is 24 years
what are the presenting symptoms of DI?
- Polyuria
- Polydipsia
- Nocturia
what are the signs of DI?
• If fluid intake < fluid output, signs of dehydration will be present o tachycardia o reduced tissue turgor o postural hypotension o dry mucous membranes
what might the blood results show for DI?
o U&Es and Ca2+
o Increased plasma osmolality
o Decreased urine osmolality
how does a water deprivation test work?
o Water is restricted for 8 hrs
o Plasma and urine osmolality are measured every hour for 8 hrs
o STOP the test if the fall in body weight is > 3%
o Desmopressin is given after 8 hrs and urine osmolality is measured
how to treat cranial DI?
o Give desmopressin
how to treat nephrogenic DI?
o Thiazide diuretics (chlorothiazide)
complications of DI?
- Hypernatraemic dehydration
* Excess desmopressin –> hyponatraemia
what is the prognosis for patients with DI?
- Cranial DI may be transient following head trauma
* It may be cured by removing the cause
