The Paraneoplastic syndromes include the disorders that accompany benign or malignant tumors but are not directly related to mass effects or invasion by the primary tumor or its metastases. Neoplastic cells can produce a variety of peptides that exert biologic actions at local and distant sites and can elicit responses that cause a variety of hormonal, hematologic, dermatologic and neurologic symptoms. Almost every type of malignancy has the potential to produce hormones or cytokines or to induce immunologic responses. Lung cancers, both non-small cell and small cell, are capable of producing a variety of paraneoplastic syndromes. The majority of such syndromes are caused by small cell carcinomas, including many endocrinopathies. Syndrome of inappropriate antidiuretic hormone (SIADH) has been commonly associated with small cell carcinoma and is often seen in these patients. However, SIADH associated with squamous cell carcinoma has rarely been reported on, and the mechanism for this rare association is still unknown. We present here a case of a 77-yr-old man who developed SIADH caused by squamous cell carcinoma of the nasopharynx.

Although hyponatremia is a common electrolyte disorder, its evaluation and management are not well defined. When diagnosed, hyponatremia should be categorized based on four criteria: volume status, urinary Na+, serum K+, and acid-base balance. This approach helps to determine what the cause of hyponatremia is and how it should be treated. Initially, hypovolemic hyponatremia, including cerebral salt wasting syndrome (CSWS), is treated by volume resuscitation and salt supplementation. Euvolemic hyponatremia, including the syndrome of inappropriate secretion of antidiuretic hormone (SIADH), is treated by fluid restriction and salt supplementation, and hypervolemic hyponatremia is treated by fluid restriction and salt restriction. Hyponatremia can be managed well using these primary treatments and medications.