Give (4) general etiologic categories behind the development of SIADH and a few examples of each.
- Lung disease (infection, asthma, cystic fibrosis)
- Cerebral/Intracranial (MS, Guillain-Barre, trauma, infection)
- Drugs (desmopressin, diuretics, SSRIs, chemotherapy, linezolid)
- Miscellaneous (HIV, nausia, acute intermittent porphyria)
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?
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
Describe SIADH management
- Fluid restriction
- IV salt solution
- Vasopressin receptor antagonists
- Loop diuretics
What is the purpose of administering demeclocycline in the management of SIADH?
It inhibits the collecting tubule response to AVP
Name two vasopressin receptor antagonists commonly used in the management of SIADH and discuss their mechanism of action in SIADH
conivaptan and talvaptan
Block V2 receptors, thereby limiting AQ2 channels and reducing water permeability
Name two diuretics commonly used in the management of SIADH and discuss their purpose in treatment of this disease
furosemide and bumetanide
These diuretics disrupt the renal medullary gradient (mechanism of action of loop diuretics)
Name the two major types of Diabetes Insipidus (DI) and compare their respective etiologies
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)
- Caused by renal resistance to AVP
- Underlying causes include: x-linked recessive disorders, hypokalemia, hypercalcemia, renal diseases, drugs (e.g. lithium)
Are DI patients typically hypovolemic, euvolemic, or hypervolemic?
In the setting of polyuria with non-osmotic diuresis, what is an alternative to dianosis of DI? How might we tell the difference?
Use water restriction test: if plasma osmolality is in normal range, psychogenic polydipsia is more likely
During and H2O deprivation test, a >50% increase in urine osmolality following administration of desmopressing is indicative of what?
Partial central DI
Normal, primary polydipsia, or nephrogenic DI (differential depends on absolute urine osmolality)
What drug is used for the treatment of central DI?
DDAVP (desmopressin, 1-deamino-8-D-arginine vasopressin)
What is the treatment approach for nephrogenic DI?