Disorders of the posterior pituitary

Question 1

Disorders of posterior pituitary

Answer 1

Diabetes insipidus, SIADH (syndrome of inappropriate secretion of ADH)

Question 2

Diabetes insipidus, central type (ADH deficiency)

Answer 2

Major causes are: trauma, tumors of the hypothalamus, rare inflammatory diseases (histiocytosis X, sarcoidosis), intracranial bleeding, Sheehan syndrome, congenital forms.
Tests for central type of diabetes insipidus: Oral water and salt test (20ml/kg water and 0.9% NaCl) on two consecutive days. In normal individuals the diuresis after salt intake is less than before salt intake.
Treatment of central type of diabetes insipidus: ADH-analogue called desmopressin. Can be administered intranasally (nasal spray) or through tablets (3x 100-200 micrograms/day).

Question 3

Diabetes insipidus, nephrogenic type

Answer 3

A disorder of renal ADH action, rather than a deficiency of ADH. Two major forms of the disease: rare congenital form, acquired form (chronic renal disease, metabolic disturbances). Treatment through NSAIDS - which decreases the polyuria and increases osmolarity, Tiazide - mild diuretics.
It is transitional in pregnancy due to an increased metabolism of ADH.

Question 4

Primary polydipsia

Answer 4

Psychological disorder

Question 5

Symptoms of diabetes insipidus

Answer 5

Polyuria (up to 18-20 liters/day in severe cases.
Polydipsia.
Low urinary density and urinary osmolarity.
DI patients cannot concentrate urine even in the case of fluid intake restriction.

Question 6

General information of SIADH

Answer 6

It is usually considered a major characteristic of paraneoplastic syndrome. Can be secondary to small cell lung cancer, carcinoids, or prostate cancer.

Question 7

Consequences of SIADH

Answer 7

Severe hyponatremia (often less than 120mmol/L)
Serum hypoosmolarity (often less than 275mOsm/kg)
Coma and seizures in severe forms

Question 8

Diagnostic signs of SIADH

Answer 8

Hypoosmolar serum, and highly concentrated urine
Hyponatremia, high urinary Na concentration
Lack of edema

Question 9

Differential diagnosis (causes other than paraneoplastic)

Answer 9

Hypothyroidsm, Addisons-disease, hypopituitarism, drugs, CNS diseases

Question 10

Treatment of SIADH

Answer 10

In severe cases (when serum Na is less than 120 mmol/L) Hypertonic salt infusion, goal is 125 mmol/L Na conc. Speed of normalization cannot be larger than 0,5 mmol/h, due to danger of central pontine myelinolysis.
In milder cases (when serum Na is more than 120mmol/L) fluid restriction is used. Daily intake as low as 800-1000ml. Demeclocyclin can also be used as it inhibits renal ADH action in chronic cases.