The type III defect is characterised by normal and appropriate osmoregulation of the hormone except under conditions of plasma hypotonicity when there is constant non suppressible vasopressin secretion. It is rarely seen in malignant disease. The abnormality may be due to a persistent ΓÇÿleakΓÇÖ of vasopressin resulting from neurohypophysial damage, loss of inhibitory osmoregulatory neurones, or persistent nonosmotic stimulation.
