Syndrome of inappropriate antidiuretic hormone classification

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Vindhya BellamKonda, M.B.B.S [2]

Overview

SIADH may be classified into several sub-types based on the pattern of AVP (arginine vasopressin) secretion across a range of plasma osmolalities into type A, type B, type C and type D.

Classification

SIADH may be classified into several sub-types based on the pattern of arginine vasopressin (AVP) secretion across a range of plasma osmolalities:

Classification	Features
TypeA	Accounts for about 60-70% of SIADH Excessive secretion of AVP is noted Associated with lung cancer and nasopharyngeal tumors Patients are more susceptible to development of severe hyponatremia
Type B	Accounts for (20–40%) of the cases Secretion of AVP occurs at lower than normal plasma osmolalities
Type C	Failure to suppress AVP secretion at plasma osmolalities below the osmotic threshold Occurs due to dysfunction of inhibitory neurons in the hypothalamus, leading to persistent low-grade basal AVP secretion
Type D	Low or undetectable AVP levels and circulating AVP response is not defective Nephrogenic SIADH (NSIAD) may be attributed to this condition Associated with gain-of-function mutations in the V2 receptor leading to a clinical picture of SIADH, with undetectable AVP levels The condition is inherited in an X-linked manner, although heterozygous females may have inappropriate antidiuresis of varying degrees.