Polyuria

Nephrology Consult:

Initial Leading Diagnosis:   Cerebral Salt Wasting (CSW)

Fludrocortisone is started

Heparin is switched to apixaban

Why avoid heparin in this case?

Rare cause of inappropriate sodium wasting; controversial as to whether CSW even exists [Palmer, B. 2021].

Occurs in context of cerebral disease; in this case felt to be related to Wernickes Encephalopathy, but in general CSW is most commonly subarachnoid hemorrhage [Rose BD, Post TW. 2001. p709]

The mechanism is unknown, but it may reflect a protective mechanism to reduce intra-cranial pressure; possible that cerebral pathology inhibits RAAS [Palmer, B. 2021]; may also involve brain naturiuretic peptide [Rose BD, Post TW. 2001. p709]

Sometimes confused with SIADH, since it may present with hyponatremia (though not always).

In terms of physiology, why might hyponatremia occur in CSW?

Unlike SIADH, fluid restriction may be harmful; requiures thoughtful replacement of lost isotonic volume [Palmer, B. 2021].

Fludrocortisone may also be adminisetered; one RCT of 36 patients with tuberculous meningitis and CSW found that fludrocortisone along with volume repletion resulted in earlier normalization of serum sodium compraed to management with volume repletion alone; notably, there was no difference in resolution of polyuria or in hospital mortality [Misra et al 2018].

Why might fludrocortisone have this effect on serum sodium? And what dangerous complication may arise from fludrocortisone?

Patient Outcome:

The patient's polyuria resolved after two weeks, and fludrocortisone was discontinued.

Ultimately, it was not clear whether this was truly CSW or appropriate excretion of extracellular volume (recall that the patient did have LE edema).