Syndrome of inappropriate antidiuretic hormone secretion due to recurrent oral cancer.

Hyponatremia is a common metabolic disorder in clinical practice and is associated with significant morbidity and mortality, especially among the elderly. Hyponatremia resulting from the syndrome of inappropriate secretion of antidiuretic hormone (SIADH) has been reported in association with neoplasia (including a few reports in patients with head and neck malignancies) and may represent a paraneoplastic condition. Patients with SIADH present with signs and symptoms that cannot be explained by the primary tumour mass effect or its metastases. We describe a 67-year-old male patient with oral squamous-cell carcinoma of recent recurrence admitted because of symptomatic severe hyponatremia resulting from SIADH and discuss the principles of the diagnostic approach and appropriate management.