Clinical quiz

Abstract

Case summary. Nephrology consultation was requested by the neurosurgical service for an 18-year-old male who developed polyuria following resection of recurrent craniopharyngioma. Review of the patient's medical history showed that his brain tumor was first detected when he was 10 years old. Surgical resection at that time was followed by the development of panhypopituitarism and diabetes insipidus requiring chronic hormonal replacement therapy. At 14 years of age, recurrent tumor was treated with radiation and a ventriculo-peritoneal shunt was placed. Tumor regrowth led to another surgical resection 6 days ago. The procedure went smoothly and his recovery was uncomplicated until yesterday when he developed polyuria followed by headache and increasing lethargy. He has just had a generalized tonic-clonic seizure. His medications include Synthyroid (levothyroxine sodium), carafate, hydrocortisone and desmopressin acetate.Examination revealed an obese, postictal adolescent male who was afehrile, tachycardic (pulse 102/rain) and relatively hypotensive (blood pressure of 104/66 mmHg). His chest was clear and cardiac auscultation normal. He appeared to have adequate peripheral perfusion. Urinalysis showed specific gravity 1.012, pH 6, negative dipstick and unremarkahle microscopy. Current serum chemistries are: sodium (Na) 123 mEq/1, potassium (K) 3.4 mEq/1, chloride (CI) 92 mEq/1, bicarbonate 25 mEq/1, blood urea nitrogen 17 mg/dl (6.1 rmnol/1), creatinine 0.6 mg/dl (53 gmol/1), glucose 118 mg/dl (6.5 retool/l), uric acid 5.2 mg/dl (309 pmol/1) and osmolality 259 mmol/kg. Urine chemistries show Na 224 mEq/1, K 22 mEq/1, CI 261 mEq/1, creatinine 5 mg/dl (442 ~tmol/1) and osmolality 509 retool/ kg. Fractional excretion of Na is 21%. His fluid balance over the past several days is shown in Table 1.

Cerebral Salt-Wasting Syndrome

“…Most case reports did not include results of serum potassium, suggesting that hypokalemia was not a prominent feature. In two reports [11, 12], hypokalemia (2.8 and 3.4 mEq/l, respectively) was shown, but renal K wasting was not documented. Likewise, plasma renin activity has not been found to be elevated [4, 5, 7, 17].…”

“…Low blood pressure is also cited as evidence for dehydration in patients with CSW [11, 12, 19]. However, chronically sick patients commonly have low blood pressure, and impaired baroreceptor reflexes, which are often associated with prolonged bedrest, can result in orthostatic hypotension in the absence of volume depletion.…”

“…Indeed, one must be suspicious of any claim for renal sodium wasting in cases of cerebral salt wasting that were published before 1957 [3]. A large number of cases have been described since 1957 as examples of cerebral salt wasting, and in some of these case reports, an attempt has been made to prove the depleted state of effective vascular volume [4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19]. However, careful examination of the data in these reports casts considerable doubt on the validity of much of the evidence for volume depletion.…”