Abstract
The syndrome of inappropriate antidiuretic hormone secretion (SIADH) is a common cause of euvolemic hyponatremia, resulting from non-osmotic release of antidiuretic hormone (ADH). SIADH is frequently associated with neurological conditions, including traumatic brain injury (TBI). TBI-associated SIADH usually develops within days to weeks and resolves within a few weeks. We present the case of a 74-year-old man who, after a fall resulting in TBI, initially had normal sodium levels. Fifteen days later, he developed moderate-to-severe hyponatremia (120 mmol/l) and significant neurological symptoms. Treatment with urea effectively normalized his sodium levels and resolved symptoms. However, recurrent hyponatremia persisted for over six months whenever urea treatment was discontinued. This unusual duration of TBI-associated SIADH underscores the importance of long-term follow-up in the management of post-traumatic hyponatremia. LEARNING POINTS: While the syndrome of inappropriate antidiuretic hormone secretion (SIADH) is typically transient, it can persist after even minor head trauma, highlighting the importance of long-term follow-up in cases of post-traumatic hyponatremia.Urea therapy is effective and well-tolerated for managing chronic hyponatremia in SIADH, offering a sustainable long-term treatment option.Even mild hyponatremia can lead to subtle but impactful cognitive and motor symptoms.