ABSTRACT BACKGROUND: Hyponatremia is a commonest electrolyte imbalance which is defined as "serum sodium level less than 135mEq/L". It is seen especially in elderly patients presenting in emergency department of hospitals. There are wide range of differentials in hyponatremic patients but it can be the initial sign of pituitary disease specifically in old age population. Diagnosis can often be challenging because symptoms can be attributed to normal aging process and high index of clinical suspicion is necessary. CASE PRESENTATION: Here we present the case of 61-year old female presented in our facility with history of vomiting, drowsiness and fatigue for 2 days before admission. On investigating, her CBC, LFT's, RFT's and urine R/E were within normal limits. Serum electrolytes showed hyponatremia. CXR was also normal. As patient was not in fluid overload, so our differentials based on euvolumic hyponatremia included syndrome of inappropriate anti-diuretic hormone secretion(SIADH), severe hypothyroidism or glucocorticoid insufficiency. Urine osmolarity was not in range of SIADH. Serum cortisol was normal. FSH, LH, estrogen and progesterone were low although these should be high as patient was post-menopausal. Prolactin was normal. MRI brain with contrast showed supra and intrasellar mass consistent with pituitary macroadenoma. Depending on presentation and investigations, Non-functioning pituitary adenoma(NFPA) presenting with panhypopituitarism complicated by hyponatremia was the final diagnosis. CONCLUSION: Our case highlights the importance of diagnosing NFPA in elderly patients who present with hyponatemia which can often be challenging and should not be delayed as this is life-saving, hence targeted treatment should be started as soon as possible.

Keywords: KEY WORDS: hyponatremia, non-functioning pituitary adenoma, macroadenoma