From renal salt wasting to SIADH.

Hyponatraemia is common following major head injury and is associated with significant morbidity and mortality. A 20-year-old man presented with reduced consciousness after head trauma and was found to have a fractured skull base with bilateral frontal contusions. On day 3 of his admission, he developed hyponatraemia with raised urine sodium and osmolality, despite receiving dexamethasone and intravenous fluid therapy. His hyponatraemia worsened after the treatment with fluid restriction and oral salt. He was in negative fluid balance suggesting possible renal salt wasting. A trial of isotonic normal saline resulted in a further fall in serum sodium level. He was subsequently treated for suspected syndrome of inappropriate ADH with a hypertonic (3%) saline infusion. His sodium level and neurological status improved. This case report illustrates the confounding factors that commonly affect clinical decision-making when treating patients with hyponatraemia following head injury. The guidelines for diagnosis and management are discussed.