Introduction: Syndrome of inappropriate antidiuretic hormone secretion (SIADH) can cause euvolemic hyponatremia, especially in patients with head and neck malignancy and surgeries or post- thyroidectomy histories. This condition increases the therapeutic challenge and the risk of recurrent hospitalizations.
Case Presentation: A 70-year-old patient with a history of total laryngectomy secondary to laryngeal squamous cell carcinoma, partial pharyngectomy, and papillary thyroid carcinoma status post thyroidectomy, presented to the emergency department with acute chest pain, nausea, and vomiting. Cardiac markers were negative for acute coronary disease, while her serum sodium was 116 mmol/L, and a serum osmolality of 246 mOsm/kg, urine osmolality 670 mOsm/kg, urine sodium of 38 mmol/L, and serum uric acid of 2.4 mg/dL. The patient was admitted to the intensive care unit (ICU) for severe hyponatremia. She was managed with fluid restriction, oral urea, and hypertonic saline. Basic metabolic panels (BMPs) were followed up every three hours. Urine studies confirmed the diagnosis of SIADH. She received tolvaptan at 7.5 mg once, resulting in rapid and sustained correction of serum sodium to 134 mmol/L without neurologic complications. She was discharged with stable sodium levels and experienced several admissions for recurrent hyponatremia with serum sodium of 120s mmol/L, each time responding well to tolvaptan.
Discussion: This case emphasizes the clinical challenge of managing recurrent severe SIADH in patients with head and neck malignancy. It demonstrates that low-dose tolvaptan may serve as an effective therapeutic choice for refractory SIADH. However, the cost of tolvaptan could be a barrier for outpatient settings.