<prompt> A 36-year-old man is brought to ER by his wife because of lethargy, weakness and confusion. Serum sodium and serum osmolality are markedly decreased. Urine osmolality is increased. These findings are most likely related to which of the following?Bronchogenic carcinomaThymomaSmall cell carcinoma of lungRenal cell carcinoma  <response>: - Given clinical features suggests the diagnosis of syndrome of inappropriate ADH SIADH secretion. SIADH - Associated with ADH excess, which causes resorption of excessive amount of free water, resulting in hyponatremia. - Causes of SIADH Secretion of ectopic ADH by malignant neoplasms small-cell carcinomas of lung, intracranial neoplasms; Non-neoplastic diseases of lung Local injury to hypothalamus neurohypophysis. - CF- Hyponatremia, cerebral edema neurologic dysfunction. - Cardinal features- Marked in both serum sodium osmolality Urine osmolality. - Although total body water is increased, blood volume remains normal peripheral edema does not develop. 