Analysis:
A dehyrated patient (high serum sodium) with an increased volume of dilute urine
(polyuria) suggests diabetes insipidus. Diabetes insipidus results from failure of vasopressin (ADH)
secretion by the posterior pituitary (neurogenic diabetes insipidus) or failure
of the kidney collecting ducts to respond to vasopressin (nephrogenic diabetes
insipidus). In either case, the kidney does not reabsorb water appropriately in the collecting
ducts, yielding a dilute urine unreponsive to the body's hydration status.
In this case, there are no neurologic or hormonal symptoms to support a
diagnosis of a neurogenic cause. However, lithium therapy is associated with a
drug-induced diabetes insipidus in a portion of patients (you'll learn about this
later in pharmacology).
Diagnosis:
Nephrogenic diabetes insipidus, associated with lithium therapy.