Secondary adrenal insuffi ciency presenting as hyponatremia. Report of one case Hyponatremia can be a marker of an underlying disease. We report a 52 years-old male with Diabetes Mellitus who consulted for an episode of nausea and vomiting lasting four days. His baseline serum sodium was 118 mEq/L. He had no neurological defi cit. Hyponatremia was initially interpreted in context of gastrointestinal fl uid loss but correction with saline solution was poor. His urine sodium was 105 mEq/L and his

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... urine osmolality was 281 mOsm/L, so an Inappropriate Secretion of Antidiuretic Hormone Syndrome was suspected. Later, we found that the patient had a two year history of fatigue, weakness, anorexia, frequent nausea, vomiting and diarrhea, loss of libido and decreased axillary and pubic hair. Thyroid-Stimulating Hormone (TSH) was normal and serum Cortisol < 1 µg/dL. A CT scan showed a sellar mass compatible with a macroadenoma. There was also a moderately high serum prolactin and low testosterone, thyroxin and growth hormone levels. The visual fi eld examination showed right temporal hemianopsia. The patient was treated with steroids with a very good clinical response and serum sodium normalization. Subsequently a transsphenoidal excision of the tumor was performed and replacement of the other hormones was started. Now the patient remains asymptomatic. (Rev Med Chile 2010; 138: 1144-1147.