Snap Shot 25 year old male complains of a unabated thirst that began three weeks ago. He is constantly drinking and goes to the bathroom around five times a night. He has lost five pounds over the last few weeks, and is on lithium for a bipolar disorder. His BP is 115/70. Introduction Central: decreased ADH secretion caused by: idiopathic trauma pituitary infection (fungal, TB) Nephrogenic: ADH resistance caused by: drugs (lithium, amphotericin B) severe hypokalemia (makes tubules resistant to ADH) Think of as inverse of SIADH Presentation Symptoms polyuria polydipsia nocturia Evaluation Diagnose with water deprivation test hold all water, administer vasopressin (ADH) measure urinary osmolarity in response to vasopressin (ADH) administration Urine specific gravity < 1.010 Urine osmolarity < 200 Serum osmolarity > 300 Treatment Central: treat with DDAVP/desmopressin or chlorpropamide Nephrogenic: treat with: increased water intake sodium restriction thiazide diuretics increase levels of aquaporin 2 in collecting system