Mechanism: destruction of vasopressin by vasopressinase (oxytocinase, cysteine aminopeptidase)
Clinical features:
(1) onset of diabetes insipidus during pregnancy, with production of a large volume of dilute urine
(2) pre-eclampsia in many affected patients
(3) failure to respond to exogenous vasopressin
(4) response to desmopressin (not destroyed by the vasopressinase)
(5) reversal on delivery
(6) normal lactation after delivery
Laboratory features:
(1) very low serum levels of vasopressin
Differential diagnosis:
(1) Sheehan's syndrome
(2) lymphocytic hypophysitis
(3) drug-induced diabetes insipidus
(4) nephrogenic diabetes insipidus
(5) previously unrecognized pre-existing or evolving diabetes insipidus
