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Disorders of the posterior pituitary gland 

Disorders of the posterior pituitary gland

Chapter:
Disorders of the posterior pituitary gland
Author(s):

Aparna Pal

, Niki Karavitaki

, and John A. H. Wass

DOI:
10.1093/med/9780199204854.003.1303

August 28, 2014: This chapter has been re-evaluated and remains up-to-date. No changes have been necessary.

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date: 28 March 2017

The posterior pituitary produces arginine vasopressin, which has a key role in fluid homeostasis, and oxytocin, which stimulates uterine contraction during birth and ejection of milk during lactation.

Cranial diabetes insipidus is the passage of large volumes (>3 litres/24 h) of dilute urine (osmolality<300 mOsm/kg) due to vasopressin deficiency, and most commonly occurs as a consequence of trauma or tumour affecting the posterior pituitary. Diagnosed by a water deprivation test revealing urine osmolality less than 300 mOsml/kg with concurrent plasma osmolality more than 290 mOsml/kg after dehydration, with urine osmolality rising to more than 750 mOsml/kg after desmopressin. MRI of the neurohypophysis is required to delineate the cause. Mild polyuria can be managed simply by ensuring adequate fluid intake; treatment with the long-acting vasopressin analogue, desmopressin (desamino, D-8 arginine vasopressin; DDAVP), is used for more severe cases.

Syndrome of inappropriate antidiuresis (SIADH)—diagnosed when there is hyponatraemia with hypotonic plasma (osmolality <270 mOsm/kg), inappropriate urine osmolality (>100 mOsm/kg) and urinary sodium >20 mmol/litre, together with (1) no evidence of volume overload or hypovolaemia, and (2) normal renal, adrenal, and thyroid function. Few patients satisfy these strict criteria, but many conditions, e.g. malignant diseases, chest diseases, central nervous system disorders and drugs, have been implicated. Aside from treatment (when possible) of the underlying cause, management requires fluid restriction and (rarely) infusion of hypertonic saline (see Chapter 21.2.1 for further discussion). Blockade of renal vasopressin receptors (V2) would be a logical treatment, and several V2 receptor antagonists are in clinical trials.

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