Diabetes insipidus (DI) is a deficiency of ADH which may be lifelong and includes the neurogenic or nephrogenic (seen infrequently) types. Secondary DI is the most common type and is caused by any insult to the head and is a complication of pituitary surgery.

The surgery is known as a transsphenoidal hypophysectomy and is used to remove a tumor in the brain or the anterior lobe of the pituitary gland. It may be performed via a sublabial (under the lip) or transnasal (through the nose) approach.

Syndrome of inappropriate ADH (SIADH) is a surplus of ADH which may be a rare neurogenic type. If it is secondary, it is primarily caused by brain issues.

SIADH is a Surplus of ADH resulting in fluid retention (water intoxication), cerebral edema, and dilutional hyponatremia. Clinical manifestations are due to the hyponatremia leading to a change in mental status. Lab effects include a decrease in Na+, K+, and serum osmolarity due to the dilution. Serum sodium level around 110 mEq/L can lead to seizures, coma, and death. Urine specific gravity will be high due to the low urinary output.

Treatment for SIADH includes fluid restriction of 800-1,000 mL per day, diuretics such as furosemide (Lasix) as initial therapy, and 3% hypertonic saline cautiously to increase serum sodium level. Long-term drug therapy may also be considered using tolvaptan (Samsca) which is a vasopressin receptor agonists.

• ADH: Don’t void.
• DI is a Deficit of ADH → ↑ Urine and Dehydration → Treated with DDAVP
• SIADH is a Surplus of ADH → ↓ Urine and Sodium imbalance (↓ Na+)
• Any insult to the head can result in DI or SIADH.

In preparing for the NCLEX exam, it is important to remember that ADH balance may be due to any insult to the head or related to a problem with the pituitary, including surgery on the gland. DI is a Deficit in ADH and results in low urine output and hypernatremia. It is primarily treated with DDAVP. SIADH is a Surplus in ADH and results in a low dilutional Sodium level which can be fatal.