Hyponatremic seizure associated with acute respiratory infection

A 66-year-old woman was admitted to our hospital because of vomiting and appetite loss. For the 2 days prior to admission, she had a cold, which had developed into acute viral bronchitis on admission. Because laboratory data on admission showed hyponatremia, intravenous infusion of Ringer's lactate solution was started. However, generalized seizures appeared, and she developed a coma on the day of admission. Her plasma antidiuretic hormone (ADH) level was high in the context of a low serum osmolality on the second hospital day. The infusion rate was increased, and the patient's consciousness level returned to normal. However, her normalized serum Na level declined again as she drank much water to reduce throat discomfort. As the throat discomfort caused by the throat inflammation improved with azulene gargling, her water intake was reduced, and the serum Na concentration returned to normal. Thus, polydipsia caused by a throat inflammation partially contributed to hyponatremia in this patient. We note that increased ADH secretion has been reported in adults with acute respiratory infection. Therefore, we concluded that polydipsia caused by the throat inflammation, plus increased ADH secretion, resulted in hyponatremia in this patient. We should pay attention to the behavior of drinking extra fluid in patients with acute respiratory infections.