• Clinical science

Syndrome of inappropriate antidiuretic hormone secretion (SIADH)

Abstract

Syndrome of inappropriate antidiuretic hormone secretion (SIADH) is an endocrine disorder caused by increased ADH secretion in the pituitary gland (e.g., due to infection, drugs), ectopic production of ADH (e.g., small cell lung carcinoma), or enhanced stimulation of ADH in the kidneys as a result of a gene mutation. Hyponatremia develops as a result of increased water retention in the kidneys (not due to sodium deficiency) and systemic fluid overload. SIADH is usually asymptomatic and hyponatremia is often an incidental finding in laboratory results. In mild cases, symptoms include loss of appetite and nausea; in severe cases, seizures and altered consciousness can occur. Treatment depends on the severity of the disease and includes fluid restriction (asymptomatic patients) to hypertonic saline administration (severe cases).

Etiology

References:[1][2]

Pathophysiology

For more information regarding ADH secretion and regulation, see antidiuretic hormone.

References:[1][3][4]

Clinical features

References:[4]

Diagnostics

SIADH patients are usually euvolemic, normotensive, and have no edema. An hyponatremic patient with edema should raise suspicion of other conditions (e.g. congestive heart failure).
References:[4]

Differential diagnoses

See: “ Hyponatremia

The differential diagnoses listed here are not exhaustive.

Treatment

The sodium serum levels may increase by a maximum of 10 mmol/L within 24 hours or 0.5 mmol/L per hour. A rapid increase in serum sodium can lead to central pontine myelinolysis!
References:[1][3][4]