Final answer:
Cerebral salt wasting (CSW) and Syndrome of Inappropriate Antidiuretic Hormone (SIADH) differ in urine osmolality, plasma osmolality, volume status, and serum sodium levels. SIADH typically results in hypoosmolar hyponatremia with high urine osmolality, while CSW presents with salt and water loss, causing hyponatremia with potential hypo- or normovolemia.
Step-by-step explanation:
Differentiation between cerebral salt wasting (CSW) and Syndrome of Inappropriate Antidiuretic Hormone (SIADH) involves comparing a number of factors, including urine osmolality, plasma osmolality, volume status, and serum sodium levels.
- Urine osmolality: In SIADH, urine osmolality is typically high as the body continues to reabsorb water due to excessive ADH despite normal or low plasma osmolality. In CSW, urine osmolality can also be high but results from renal salt wasting.
- Plasma osmolality: Plasma osmolality tends to be low in SIADH because of the dilutional effect of retained water. CSW, on the contrary, may lead to a normal or slightly elevated plasma osmolality due to dehydration from renal salt and water loss.
- Volume status: SIADH generally presents with a euvolemic or slightly hypervolemic state due to water retention. CSW is associated with hypovolemia because of the loss of both sodium and water.
- Serum sodium levels: Both disorders are characterized by hyponatremia; however, the hyponatremia in CSW is due to sodium loss, whereas in SIADH it is due to excess water.
Regulation of urine volume and osmolarity is a major function of the collecting ducts, controlled by the ADH hormone. Stress increases osmolality which usually would decrease ADH secretion, but in the case of SIADH, ADH is inappropriately secreted despite normal or low osmolality. This contrasts with CSW where ADH is not primarily involved, and the condition is more related to renal salt loss.