Syndrome of inappropriate secretion of anti-diuretic hormone (SIADH) as an initial presenting sign of non small cell lung cancer-case report and literature review.

Association of SIADH with malignancy was first reported in 1957, when it was described in two patients with bronchogenic carcinoma. While the association with small cell lung cancer (SCLC) is well known, that with non small cell lung cancer (NSCLC) has been rarely reported. We report a case of 70 year old male who was found to have hyponatremia secondary to SIADH. Radiological tests revealed right hilar lung mass with mediastinal adenopathy. Bronchoscopic biopsy revealed non-small cell lung cancer of type squamous cell. Magnetic resonance imaging (MRI) of brain showed metastatic lesions, thereby confirming diagnosis of metastatic lung cancer. Paraneoplastic syndromes occur in 10% of lung cancer cases and they represent a group of disorders related to secretion of functional polypeptides or hormones from tumor cells. SIADH is more commonly described in conjunction with small cell lung cancer but there are a few case reports describing it's occurrence after initiation of therapy for NSCLC such as radiation and chemotherapy. The mechanism for this phenomenon is not known. Unlike infectious causes, hyponatremia as initial presentation is an uncommon feature of malignancy-associated SIADH. In the lung cancer population, hyponatremia has been identified as a negative prognostic factor in hospitalized patients and those with advanced-stage disease. Malignancy should be a consideration in the diagnostic evaluation of SIADH, irrespective of the time of presentation.