Chronic Hyponatremia Following Mild Traumatic Brain Injury: A Case of Persistent Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH) in a Young Adult

Hyponatremia is a well-recognized complication of traumatic brain injury (TBI), most commonly resulting from syndrome of inappropriate antidiuretic hormone secretion (SIADH) or cerebral salt wasting (CSW) syndrome. While SIADH is frequently described following moderate to severe TBI, persistent SIADH after mild TBI is rare and has been infrequently reported. A 25-year-old man was admitted to Lady Reading Hospital following a road traffic accident resulting in mild TBI. He experienced an uncomplicated neurological recovery, and neuroimaging showed no significant intracranial abnormalities. During hospitalization, he developed symptomatic hyponatremia. Biochemical evaluation, including the assessment of serum and urine osmolality and urinary sodium, was consistent with SIADH after alternative causes of hyponatremia were excluded. Initial management with fluid restriction resulted in the normalization of serum sodium levels. However, recurrent episodes of hyponatremia occurred over the ensuing months, necessitating prolonged fluid restriction and regular outpatient monitoring. No other underlying cause of persistent SIADH was identified despite further evaluation. This case demonstrates that persistent SIADH can occur even after mild TBI despite normal neuroimaging and an initially favorable neurological recovery. Clinicians should maintain a high index of suspicion for SIADH in patients who develop hyponatremia following mild head injury and recognize the potential for recurrence. Long-term follow-up with the periodic monitoring of serum sodium may facilitate timely intervention and help prevent complications associated with chronic hyponatremia.