Endocrine

Question 1

Aetiology of Diabetes Insipidus

Answer 1

• Central (deficiency of ADH) - primary is idiopathic, secondary (2/3) is brain tumour, neurosurgery, TBI, pituitary ischaemia, infection
• Nephrogenic (defective ADH receptors): Hereditary (very rare), Acquired (medications (lithium), hypokalaemia, hypercalcaemia, renal disease, pregnancy)

Question 2

Investigations of Diabetes Insipidus

Answer 2

Lab: EUC (hypernatraemia), plasma osmolality (increased), urine osmolality (decreased), Water deprivation test (plasma osmolality stays high, urine osmolality stays low), 24 hr urine volume (>=50mL/kg/day), consider MRI brain

Question 3

Management of Diabetes Insipidus

Answer 3

1. Treat underlying cause where posisble
2. Supportive - low sodium, low protein diet
3. Medical - Central (give synthetic ADH) = desmopressin