Delayed postoperative hyponatremia in patients with acromegaly: incidence and predictive factors

Purpose: Delayed postoperative hyponatremia (DPH) is a unique complication of transsphenoidal surgery (TSS) in pituitary tumors. Growth hormone (GH) enhances renal sodium reabsorption; however, the association between postoperative GH reduction and DPH in acromegaly is unclear. This study was performed to clarify the incidence of and the predictive factors for DPH in patients with acromegaly who underwent TSS. Methods: Ninety-four patients with active acromegaly were examined retrospectively. During the postoperative course, patients with serum sodium levels ≤ 134 mEq/L were classified into the DPH group. We compared basic clinical characteristics, tumor characteristics, and preoperative and postoperative examination findings between the DPH and non-DPH groups. Results: DPH occurred in 39 patients (41.5%), and the lowest serum sodium levels were generally observed during postoperative days (PODs) 7–9. They needed a 3-day longer hospital stay than those without DPH. The DPH group had lower preoperative body weight and body mass index. In addition, a transient increase in body weight during PODs 5–7 occurred with a transient decrease in urinary volume in the DPH group. Preoperative and postoperative GH and insulin-like growth factor-1 levels did not differ between the two groups. Conclusion: The findings suggested that lower preoperative weight and a postoperative transient gain in body weight are associated with an increased risk of DPH in acromegaly patients undergoing transsphenoidal surgery.