[Oral urea in the management of inappropriate antidiuretic hormone secretion syndrome associated with Guillain-Barré syndrome, severe dysautonomia, and pheochromocytoma ‒ An exceptional clinical case].

Introduction and case report: we report the case of an 82-year-old man with pheochromocytoma and colon adenocarcinoma who developed rapidly progressive Guillain-Barré syndrome with severe dysautonomia following a recent SARS-CoV-2 infection. In this setting, he developed progressive hyponatremia secondary to syndrome of inappropriate antidiuretic hormone secretion (SIADH). Marked autonomic instability related to the coexistence of Guillain-Barré syndrome and pheochromocytoma limited conventional therapeutic options. After an inadequate response to fluid restriction and oral sodium chloride supplementation, oral urea therapy was initiated, resulting in a gradual and safe correction of serum sodium without significant adverse events. Normalization of serum sodium enabled completion of preoperative management and successful adrenalectomy and colon cancer surgery, without recurrence of hyponatremia. Discussion: to our knowledge, this is the first reported case describing the successful use of oral urea for SIADH in a patient with concomitant Guillain-Barré syndrome, severe dysautonomia, and pheochromocytoma, supporting its role as an effective and safe therapeutic option when conventional treatments are limited or ineffective.