RESUMEN
A 75-year-old man was transferred to our hospital on November 28, 2003 because of acute aggravation while being treated for interstitial pneumonia superimposed on pneumoconiosis at a local hospital. Upon admission, oxygen inhalation therapy and antimicrobial chemotherapy were started for the interstitial pneumonia. In addition, since he showed hyponatremia from admission, a saline load was administered and the clinical course was observed. However, disturbance of consciousness developed on January 5, 2004. At that time, the serum sodium was 115mEq/l. Since secretion of antidiuretic hormone (SIADH) had continued despite a low plasma osmolarity, we diagnosed syndrome of inappropriate secretion of antidiuretic hormone (SIADH). We initiated treatment with water restriction and saline load, but no remarkable improvement was observed. From February 7, 40mg /day prednisolone was started because of aggravation of interstitial pneumonia. As a result, the respiratory status and image findings improved, and serum sodium level was normalized. This case was considered to be SIADH secondary to interstitial pneumonia. Among respiratory tract diseases, SIADH is often caused by small cell lung carcinoma, although it may also occur concurrently with other respiratory tract diseases. Since hyponatremia may manifest grave disturbance of consciousness, investigation of the cause is important.