LAUSR

Background: Diabetes insipidus (DI) is a common occurrence after sellar/suprasellar surgery. However, signs of recovery after a few days should be treated with caution as this may precede a “triple response”, seen in 3.4% of the patients. In this response, initial postoperative DI gives way to a period of remission or clinically inappropriate antidiuresis before eventual recurrence of DI. Clinical Case: A 38-year-old Hispanic female was admitted to the hospital for elective transcranial resection of a suprasellar meningioma extending along the planus sphenoidale, measuring 23x19x17mm. Preoperatively, all pituitary hormones were in the normal range. On POD1, she was noted to have polyuria with urine output of >400ml/h, uptrending sodium levels (148, RR: 135-145mmol/L), low urine specific gravity (<1.005, RR:1.005-1.030) and low urine osmolality (82, RR:300-900mOsm/kg). She was diagnosed with DI and was treated with DDAVP over the following three days. Follow-up MRI was done. In addition to post-surgical changes, it showed acute ischemia in the region of the anterior commissure. After short-term improvement in her clinical status, she was noted to have decreased thirst and decreased urine output on POD6. Sodium was low at 132mmol/L. Urine specific gravity was 1.017. Serum osmolality was 258 mOsm/kg (RR:279-300 mOsm/kg). There was concern for developing SIADH vs concurrent adrenal insufficiency. Patient had received methylprednisolone perioperatively, hence AM cortisol testing would have been inaccurate. Fluid restriction, along with empiric glucocorticoid replacement, was initiated. Sodium continued to worsen with nadir of 122mmol/L and patient reported new onset headache. She was started on 3% (hypertonic) saline continuous infusion and salt tablets. Hyponatremia gradually resolved by POD13, 7 days after onset of SIADH. Salt tablets and fluid restriction were discontinued. Patient was seen in clinic on POD17 and reported normal thirst and urine output. Sodium was noted to be 143mmol/L. Conclusion: This case highlights the rare presentation of a partial triphasic sodium imbalance after resection of a suprasellar mass, with a prolonged second phase lasting for 7 days. A few studies have reported that it may last longer when pituitary gland is not damaged preoperatively, as was the case in our patient. Similarly, complete recovery may also occur if the hypothalamus and pituitary are normal preoperatively. Postoperatively, patient was noted to have an anterior commissural ischemia. This could have contributed to the fluctuations in ADH secretion, due to the rostral proximity of the hypothalamus to the anterior commissure. Despite adequate measures, sodium may continue to drop dramatically in the second phase. Patients should be monitored for changes in thirst and normalization of urine output, as these may indicate early symptoms of impending SIADH before hyponatremia develops.