Posterior Pituitary - Fareau

Question 1

Give (4) general etiologic categories behind the development of SIADH and a few examples of each.

Answer 1

1. Lung disease (infection, asthma, cystic fibrosis)
2. Cerebral/Intracranial (MS, Guillain-Barre, trauma, infection)
3. Drugs (desmopressin, diuretics, SSRIs, chemotherapy, linezolid)
4. Miscellaneous (HIV, nausia, acute intermittent porphyria)

Question 2

What combination of measured serum osmolarity, volume status, urine osmolality, and urine sodium may be indicative of SIADH? Under these conditions, what else might be on the differential?

Answer 2

SIADH is a diagnosis of exclusion

Serum osmolality: hypotonic (<275 mOsm/L)

Volume status: euvolemic

Urine osmolality: >100 mOsm/L

Urine sodium: >20 mEq/L

Adrenal insufficiency and hypothyroidism may also share these findings with SIADH

Question 3

Describe SIADH management

Answer 3

• Fluid restriction
• IV salt solution
• Vasopressin receptor antagonists
• Loop diuretics
• Demeclocycline

Question 4

What is the purpose of administering demeclocycline in the management of SIADH?

Answer 4

It inhibits the collecting tubule response to AVP

Question 5

Name two vasopressin receptor antagonists commonly used in the management of SIADH and discuss their mechanism of action in SIADH

Answer 5

**conivaptan **and talvaptan

Block V2 receptors, thereby limiting AQ2 channels and reducing water permeability

Question 6

Name two diuretics commonly used in the management of SIADH and discuss their purpose in treatment of this disease

Answer 6

**furosemide **and bumetanide

These diuretics disrupt the renal medullary gradient (mechanism of action of loop diuretics)

Question 7

Name the two major types of **Diabetes Insipidus (DI) **and compare their respective etiologies

Answer 7

Central (neurogenic) DI

• Caused by deficienct production/release of AVP
• Underlying causes include: autoimmune injury to the HT/pituitary, head trauma/surgery, cerebral hypoperfusion, tumors, infliltrative disorders (sarcoidosis, histiocytosis)

Nephrogenic DI

• Caused by renal resistance to AVP
• Underlying causes include: x-linked recessive disorders, hypokalemia, hypercalcemia, renal diseases, drugs (e.g. lithium)

Question 8

Are DI patients typically hypovolemic, euvolemic, or hypervolemic?

Answer 8

euvolemic

Question 9

In the setting of polyuria with non-osmotic diuresis, what is an alternative to dianosis of DI? How might we tell the difference?

Answer 9

Psychogenic polydipsia

Use water restriction test: if plasma osmolality is in normal range, psychogenic polydipsia is more likely

Question 10

During and H2O deprivation test, a >50% increase in urine osmolality following administration of desmopressing is indicative of what?

10-20%?

0%?

Answer 10

Central DI

Partial central DI

Normal, primary polydipsia, or nephrogenic DI (differential depends on absolute urine osmolality)

Question 11

What drug is used for the treatment of central DI?

Answer 11

DDAVP (desmopressin, 1-deamino-8-D-arginine vasopressin)

Question 12

What is the treatment approach for nephrogenic DI?

Answer 12

• Recommend low-salt, low-protein diet
• Start thiazide diuretic
• NSAID
• Consider DDAVP