Abstract
Diabetes insipidus is commonly seen following pituitary surgery. Characterized by increased urine output, hypo-osmotic urine, and serum hypernatremia, diabetes insipidus is frequently transient and may require intraopertaive mangaement. However, permanent diabetes insipidus does occur, particularly with suprasellar procedures. In such cases, treatment with desmopressin or vasopressin is necessary.
Keywords
desmopressin, diabetes insipidus, hypernatremia, pituitary, vasopressin
Case Synopsis
A 58-year-old man undergoes transsphenoidal hypophysectomy for resection of a prolactin-secreting pituitary adenoma with suprasellar extension. Ten hours after surgery, urine output exceeds 3 L/h, and the serum sodium level is 150 mEq/L.
Acknowledgment
The authors wish to thank Dr. Patricia Petrozza for her contribution to the previous edition of this chapter.
Problem Analysis
Definition
Diabetes insipidus is a syndrome characterized by polyuria, thirst, and polydipsia triggered by plasma hyperosmolarity. Neurogenic, or “central,” diabetes insipidus results from insufficient antidiuretic hormone (ADH) secretion, secondary to damage to the hypothalamic-neurohypophysial axis. Loss of approximately 90% of ADH-secreting neurons is needed for the development of clinically relevant polyuria. In contrast, nephrogenic diabetes insipidus is characterized by renal resistance to the action of ADH. Gestational diabetes insipidus usually occurs later in pregnancy and resolves 4 to 6 weeks postpartum.
An absolute deficiency of ADH results in impaired urine concentrating ability, polyuria, and a tendency toward dehydration. Most patients have incomplete neurogenic diabetes insipidus and retain a limited ability to concentrate urine and conserve free water. However, if access to water is impaired (e.g., unconsciousness, perioperative nothing-by-mouth status), hypertonic dehydration and hypernatremia may develop. Signs and symptoms of hypernatremia include psychomotor agitation, neuromuscular irritability, lethargy, coma, and seizures.
Recognition
Diabetes insipidus occurs in as many as 70% of adult patients in the first 24 hours following transsphenoidal pituitary surgery. However, the syndrome is usually transient in this setting, and studies suggest that 20% of patients are discharged with the diagnosis of diabetes insipidus. Perioperative glucocorticoid replacement may facilitate the development of polyuria. Laboratory findings characteristic of diabetes insipidus are as follows:
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A 24-hour urine volume greater than 50 mL/kg
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Urine osmolarity less than 300 mOsm/kg H 2 O
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Urine specific gravity less than 1.010
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Serum osmolarity greater than 300 mOsm/kg
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Hypernatremia (serum sodium >142 mEq/L
Chronic polyuria causes the hypertonic renal medullary concentration gradient to be “washed out.” Additional urine-concentrating mechanisms become impaired, so that polyuria increases. Alternative causes of polyuria must be eliminated to make the diagnosis of primary neurogenic or nephrogenic diabetes insipidus with confidence ( Box 70.1 ).
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