Diseases Of The Posterior Pituitary

Question 1

What are the two main diseases of the Posterior pituitary

Answer 1

1. Diabetes Isipidus

2. Syndrome of inappropriate anti diuretic hormone secretion

Question 2

What is diabetes insipidus

Answer 2

1. ADH deficiency

2. ADH unresponsive

Question 3

How is Diabetes isipidus defined?

Answer 3

Passage of large volumes of (greater than 3l/24hours) dilute urine (less than 300mOsm/kg)
It his two major forms:
1. Central (neurogenic, pituitary or neurohypophyseal) DI, decreased secretion of ADH
2. Nephrogenic DI, decreased ability to conc urine because of resistance to ADH action in the kidney

Question 4

What are the signs and symptoms if DI

Answer 4

1. Polyuria
2. Polydipsia
3. Nocturia
4. Hypernatraemia
5. Increased serum osmolality
6. Decreased urine osmolality

Question 5

How is DI diagnosed?

Answer 5

1. 24 hour urine collection
2. Serum electrolyte concentration
3. Urinary specific gravity
4. Plasma urinary osmolality
5. ADH levels

Question 6

What additional tests are carried out?

Answer 6

1. Water deprivation test (Miller Moses) to ensure adequate dehydration and maximal stimulation of ADH for diagnosis.
2. Pituitary studies

Question 7

How do you distinguish between central DI and nephrogenic DI?

Answer 7

1. Give the patient ADH and if urine osmolality increases then central DI (missing ADH)
2. If urine osmolality doesn’t change then nephrogenic

Question 8

Where is ADH made?

Answer 8

Made in the hypothalamus and stored in the posterior Pituitary.

Question 9

What cause nephrogenix DI?

Answer 9

1. Lithium
2. Demeclocycline a form of tetracycline
3. Hypercalcemia
4. Sickle cell disease

Question 10

What are the causes of central DI

Answer 10

1. Neoplasm or infiltrative lesions
2. Sarcoidosis
3. Surgery
4. Radiotherapy
5. Head injuries

Question 11

What are the causes of Nephrogenic DI?

Answer 11

1. Hypercalcemia
2. Sickle cell disease
3. Drugs (lithium, demecycline, colchinine)

Question 12

What is the treatment for Central DI

Answer 12

1. Desmopressin intranasally

2. Vasopressin subcutaneous

Question 13

What is the treatment for Nephrogenic DI

Answer 13

1. Diuretics and amiloride (calcium sparing)

2. NSAIDs

Question 14

Define SIADH

Answer 14

1. Hyponatraemia and hypo osmolality resulting from inappropriate, continued secretion or action of ADH arginine vasopressin (AVP)
2. Despite normal or increased plasma volume, which results in impaired water secretion

Question 15

What are the features of SIADH

Answer 15

1. Free water retention
2. Extracellular fluid volume expansion
3. No pedal oedema or hypertension
4. Concentrated urine
5. Hyponatraemia
6. Uosm greater than 300

Question 16

What are the symptoms of SIADH especially when Hyponatraemia is severe?

Answer 16

1. irritability
2. confusion
3. seizures

Question 17

When should you consider SIADH?

Answer 17

Consider SIADH in all cases of euvolemic Hyponatraemia.

Question 18

What is the diagnosis of SIADH

Answer 18

1. Hyponatraemia less 130mEqL
2. Plasma osm less 270osmol/kg
3. Small amounts of concentrated urine
4. Inappropriate naturesis
5. Low BUN
6. Low uric acid
7. Normal thyroid adrenal function
8. Urine sodium of greater than 20mEq/L

Question 19

What is the etiology of SIADH?

Answer 19

Pulmonary disorders:
1. Malignancies (oat cell)
2. TB, sarcoidosis
3. Lung abscess
CNS disorders
1. Head injuries
2. Stroke

Question 20

What drugs can cause SIADH

Answer 20

1. Chlorpropamide
2. Vincristine, Vinblastine, cyclophoshamide
3. SSRIs (sertraline)

Question 21

What is the management of SIADH

Answer 21

1. Restrict fluids 800-1500mls daily
2. Px demeclocyclicine
3. Lithium
   In severe confusion, convulsions:
4. Hypertonic saline IV in 3-4. hours