Adenoma mimicking hyponatremia of SIAD

Hyponatremia is a common electrolyte disorder, with prevalence as high as 20% in inpatient settings. It is classified based on volume status, urine sodium and osmolality results. While this approach might help narrow down the differential diagnoses, it can leave other diagnoses unentertained. In this case, we report recurrent and refractory hyponatremia secondary to hypocortisolism due to non-functioning pituitary macroadenoma. Interestingly, urine studies mimicked syndrome of inappropriate antidiuresis, but exclusively responded to hydrocortisone replacement. Hospital course was also complicated by hyponatremia-induced rhabdomyolysis, which is a rare complication of severe hyponatremia. We also discuss the role of anchoring heuristics and how they influence the physician's decision leading to possible diagnostic errors. One way to minimise the effect of anchoring bias on physicians is their cognitive awareness of such bias. In addition, discussing complicated cases with all members of medical team can highlight the clinician's thought processes, share uncertainty and help broaden differential diagnoses.