Electrolyte Patterns in Endocrine Disease

Hyponatremia is a serum sodium concentration below 135 mEq/L. In endocrine disease, the problem is often not a depleted body sodium supply. It is too much retained water relative to sodium. Antidiuretic hormone (ADH) tells the kidneys to conserve water. When ADH activity remains high, or when the kidneys cannot excrete free water effectively, retained water dilutes serum sodium. The brain is especially vulnerable because water shifts into brain cells when extracellular osmolality falls. Acute dilution can therefore cause cerebral edema, seizures, coma, and respiratory arrest. Three endocrine-related patterns deserve attention: - SIADH: Persistent ADH effect causes water retention despite low serum osmolality. The patient is often clinically euvolemic: not obviously dehydrated and not markedly edematous. - Adrenal insufficiency: Cortisol deficiency removes normal restraint on ADH release. Water retention and hypotonic hyponatremia may follow. Volume depletion may coexist, especially when mineralocorticoid deficiency is present. - Hypothyroidism: Reduced thyroid hormone activity can impair free-water clearance, allowing dilutional hyponatremia. Clinically significant hyponatremia is more likely with severe disease or additional triggers. The sodium value matters, but the speed of decline matters just...