RESUMO
Most of the patients with hemorrhagic fever with renal syndrome (HFRS) by Hantaviruses recover completely. However, the prevalence of hypopituitarism as sequel of HFRS may be approximately 10%. However, it is rare for hyponatremia to present as a manifestation of hypopituitarism due to HFRS. A 42-year-old Asian woman presented with anorexia, nausea, and vomiting. She had a history of HFRS 7 years ago. During her first hospital admission, her serum sodium was 103 mmol/L. The rapid adrenocorticotropic hormone (ACTH) stimulation test showed no abnormal findings suggesting the possibility of adrenal insufficiency. After she underwent fluid therapy for 5 days, her serum sodium level was slightly increased to 131 mmol/L, and her clinical symptoms were improving. The next day after she was discharged, she suffered from the same symptoms and was admitted to our hospital again. On the day of her second admission, her serum sodium was 117 mmol/L. A combined pituitary function test showed diminished function of the anterior pituitary gland, which led to secondary adrenal insufficiency. Magnetic resonance imaging findings of her sella were compatible with empty sella turcica. After the replacement of prednisolone, her serum sodium levels returned to normal. Pituitary dysfunction should be included in the differential diagnosis of severe hyponatremia, especially in patients who suffered HFRS. This case also suggests that the rapid ACTH stimulation test has limitations with regard to the differential diagnosis of primary or secondary adrenal insufficiency.