A 38‑year‑old woman, 4 months after a neurosurgical operation for recurrence of chordoma in the hypothalamic‑pituitary region, with postoperative panhypopituitarism, was admitted to our endocrine department due to cough and confusion. She was on oral hydrocortisone and levothyroxine. Upon admission, hypotension, desaturation, and crackles in the lungs were found. Laboratory tests showed elevated C‑reactive protein, hypernatremia (Na⁺, 147 mmol/l; reference range [RR], 135–145 mmol/l) and normal renal function. Following chest computed tomography that showed bilateral pneumonia, oxygen therapy, ceftriaxone, and intravenous hydrocortisone were introduced.

On the next day, an improvement in respiratory function was observed; however, hypernatremia and increased diuresis (Figure 1) were noted. By the third day, serum osmolality was 317 mOsm/kg H₂O (RR, 270–300 mOsm/kg H₂O), indicating hyperosmolar dehydration from central diabetes insipidus (CDI). Desmopressin (120 µg/day) and 0.9% NaCl infusions were initiated.

Over the next days, serum sodium level decreased more than anticipated (Figure 1). To rule out desmopressin overdosing, the drug was withdrawn. Despite this, serum sodium continued to decrease. On the tenth day, the patient’s condition deteriorated, and signs of hypovolemia occurred. Decreased serum sodium (118 mmol/l) was accompanied by high sodium concentration in the urine (192 mmol/l) and increased diuresis (5500 ml/24 h; RR, 2000–2500 ml/24 h). Due to escalating polyuria and pronounced natriuresis accompanied by hyponatremia, cerebral salt‑wasting syndrome (CSWS) overlapping with CDI was diagnosed. Desmopressin was reinitiated, fludrocortisone (0.2 mg) was added, 0.9% and 3% NaCl infusions were started, ultimately achieving stabilization of diuresis and correction of sodium levels (Figure 1).

Sodium balance disorders are common complications of neurosurgical procedures involving the pituitary gland.¹ CDI results from impaired synthesis or secretion of the antidiuretic hormone (vasopressin), which leads to decreased water reabsorption in the kidneys and the production of large volumes of diluted urine. This condition is also associated with secondary polydipsia, and treatment typically involves desmopressin, a selective agonist of vasopressin receptors.

Our patient initially presented with CDI symptoms and responded well to desmopressin. However, later life‑threatening hyponatremia, massive polyuria, and pronounced natriuresis developed. In a differential diagnosis, the syndrome of inappropriate antidiuretic hormone secretion (SIADH) was also considered due to hyponatremia and natriuresis, which are common in both CSWS and SIADH; however, the degree of natriuresis and polyuria with hypovolemic features excluded SIADH. In the treatment of CSWS, simultaneous correction of volume and sodium levels with 0.9% and 3% NaCl is necessary, along with fludrocortisone to enhance sodium reabsorption.^2-5

The coexistence of hyponatremia with polyuria and considerable natriuresis may indicate a mixed syndrome comprising CSWS and CDI; however, it is crucial to recognize both components. Misinterpreting polyuria as uncontrolled CDI and increasing desmopressin dosage can lead to severe hyponatremia, causing seizures, coma, or death. Conversely, misattributing hyponatremia to desmopressin overdose and reducing its dose can cause hypovolemic shock due to hypovolemia. Combined therapy involves fluid administration, sodium correction, careful monitoring, and medications: desmopressin and fludrocortisone.

In summary, comprehensive differential diagnosis of sodium balance disorders is essential in patients after neurosurgical operations, considering rare causes, such as CSWS combined with CDI. Understanding the underlying mechanisms and regular monitoring of serum osmolality, sodium, and fluid balance are vital for effective treatment.