Internal Medicine

Answer 5 Diabetes insipidus. Disorders of sodium homeostasis, especially hyponatremia, are not uncommon following cerebral hemorrhage, stroke, head trauma, or craniotomy. Common causes of hyponatremia in this setting include volume depletion from vomiting or poor oral intake and diuretic administration (loop diuretics or mannitol). Hyponatremia also may occur from release of antidiuretic hormone (SIADH) following any type of injury or stress to the central nervous system. Classic features of SIADH include euvolemia, hyponatremia, increased urine sodium and osmolality, and hypouricemia. Another less appreciated cause of hyponatremia in neurosurgical patients is the cerebral salt wasting syndrome. This syndrome likely results from release of atrial natriuretic peptide, leading to massive natriuresis and subsequent volume depletion, tachycardia, and increased urine sodium levels.6 Diabetes insipidus may complicate brain injury but usually manifests as polyuria and hypernatremia. REFERENCE 6. Marinella MA. Cerebral salt wasting syndrome. In: Frequently overlooked diagnoses in acute care. Philadelphia: Hanley and Belfus; 2003:43–7. Click here to return to the questions

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