DIFFERENTIAL DIAGNOSIS OF CEREBRAL SALT-WASTING SYNDROME AND SYNDROME OF INAPPROPRIATE ANTIDIURETIC HORMONE SECRETION IN A PATIENT WITH HYPONATREMIA FOLLOWING HEMORRHAGIC STROKE

Introduction. Hyponatremia frequently occurs after stroke due to cerebral salt-wasting syndrome (CSWS) or syndrome of inappropriate antidiuretic hormone secretion (SIADH). These conditions share similar features (hyponatremia, hypoosmolality of blood, high urine osmolality) but require opposing treatment approaches. Diagnostic errors often lead to cerebral edema or electrolyte disturbances, underscoring the need for precise differentiation. Case Report. A 58-year-old man with a history of hypertension and type 2 diabetes was hospitalized for hemorrhagic stroke in the right temporal lobe. On day 10 post-stroke, he developed weakness, confusion, hypotension (100/60 mmHg), tachycardia (110 bpm), dry mucous membranes, and reduced skin turgor. Laboratory findings included hyponatremia (118 mmol/L), elevated urinary sodium (70 mmol/L), serum osmolality (245 mOsm/L), urine osmolality (520 mOsm/L), and hematocrit (48 %). CSWS was favored due to hypovolemia (elevated hematocrit, dry mucous membranes) and absence of fluid retention. Treatment included 0.9 % NaCl infusion (2 mL/kg/h). Sodium levels normalized to 135 mmol/L by day 7, with clinical improvement. Conclusions. CSWS is a key cause of hyponatremia post-stroke. Differentiation from SIADH is critical: CSWS involves hypovolemia requiring fluid resuscitation, whereas SIADH involves hypervolemia requiring fluid restriction. This case highlights the importance of rapid diagnosis, monitoring, and individualized treatment to prevent complications.