SELF ASSESSMENT ANSWERS An interesting case of thirst and polyuria

Q1: What are the possible causes of thirst and polyuria in this woman? The two likely causes of thirst and polyuria in this patient are central diabetes insipidus secondary to previous pituitary surgery and hypercalcaemia. In our patient, a normal water deprivation test excluded central diabetes insipidus. Cranial surgery accounts for 20% cases of central diabetes insipidus in adults. After pituitary surgery, persistent polyuria develops only when the injury is sufficiently high in the supraopticohypophyseal tract to cause degeneration of the supraoptic and paraventricular nucleus. Thus although transient diabetes insipidus may follow any injury to the neurohypophysis, permanent cranial diabetes insipidus is uncommon after pituitary surgery. Hypercalcaemia causes transient nephrogenic diabetes insipidus manifested primarily as a defect in maximum renal concentrating ability accompanied by a reduction in glomerular filtration rate. Other factors may include reduction in medullary solute content and inhibition by calcium of adenylate cyclase activation by arginine vasopressin in hormone sensitive epithelia.