Posterior Pituitary Disorders

  1. ADH deficiency is the most important posterior pituitary dysfunction

    • Causes:

      1. Damage to the pituitary/hypothalamus by neoplasms

      2. Surgical/radiation injury

      3. Head injuries

      4. Idiopathic (deficient function of unknown cause)

    • Diabetes insipidus is the clinical syndrome that results from a deficiency of ADH action

      • Polyuria, thirst, polydipsia

      • High-normal or high serum osmolality with low urine osmolality

      • Diabetes insipidus may be neurogenic (deficient production of ADH by the pituitary) or nephrogenic (pituitary production of ADH is normal, but the renal tubules are unresponsive to ADH).

      • Laboratory analysis:

        • A water deprivation challenge can confirm diabetes insipidus and determine its type. Water deprivation must be done carefully according to accepted protocols, with close monitoring of the patient's fluid output and body weight.

  2. ADH excess: Syndrome of Inappropriate ADH (SIADH)

    • This is not a pituitary problem, but is the converse of diabetes insipidus.

    • Marked by excess water retention with hyponatremia and inappropriately concentrated urine

    • Typically paraneoplastic (small cell bronchogenic carcinoma causes 80% of cases)

    • Rarely caused by CNS lesions such as hemorrhage, thrombosis, and infections

    • Laboratory analysis:

      • Direct immunoassay for ADH

      • Challenge testing: water loading (according to established protocols and with careful monitoring of the patient) and evaluation of the rate of excretion of the water load over time.
Hypopituitarism Outline
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Last modified: 1/16/97; Author: J. Harrison