Refractory hyponatremia after traumatic brain injury unmasks adrenal insufficiency in a patient with remote steroid use.

A man in his early 60 s developed persistent hyponatremia following lumbar spine surgery complicated by traumatic brain injury with subarachnoid hemorrhage. Initial evaluation demonstrated hypotonic hyponatremia with inappropriately concentrated urine, consistent with the syndrome of inappropriate antidiuretic hormone secretio. Standard therapy including hypertonic saline and oral sodium supplementation resulted in only transient improvement. Given a history of secondary adrenal insufficiency due to long-term topical corticosteroid use, adrenal function was reassessed. An adrenocorticotropic hormone stimulation test confirmed secondary adrenal insufficiency. Initiation of hydrocortisone therapy led to sustained normalization of serum sodium. This case highlights the diagnostic difficulty of post-TBI hyponatremia and underscores the importance of considering adrenal insufficiency, even years after apparent recovery from steroid-induced hypothalamic-pituitary-adrenal axis suppression.