Hyponatremia due to adrenal insufficiency after a Mamushi bite: a case report

BACKGROUND: Mamushi bites are the most common venomous snake bites in Japan, with known complications including rhabdomyolysis and acute kidney injury; however, adrenal insufficiency as a result of snake bites has not been previously reported. We report a case of empty sella with transient adrenal insufficiency during hospitalization for a Mamushi bite. CASE PRESENTATION: An 84-year-old man was admitted to our hospital with a Mamushi bite on the right fifth finger. Serum sodium (Na) level remained in the normal range. On the ninth day of admission, he developed hyponatremia, with a serum Na level of 114 mEq/L and serum cortisol level of 4.0 μg/dL (reference value 4.5–21.1 μg/dL). His serum Na level was restored within the normal range after administration of corticosteroids with 3% NaCl solution. Both rapid adrenocorticotrophin and corticotropin-releasing hormone loading tests showed low cortisol response. Based on the results of the hormone loading tests, a diagnosis of pituitary adrenal insufficiency was made. Contrast-enhanced pituitary magnetic resonance imaging (MRI) showed primary empty sella. After discontinuation of corticosteroids, the hyponatremia did not recur, and the patient was discharged on the 24th day of hospitalization. After discharge, the patient visited an outpatient clinic, but hyponatremia recurrence was not observed. CONCLUSIONS: This is the first report of hyponatremia due to pituitary adrenal insufficiency during hospitalization for a Mamushi bite in a patient with empty sella. When hyponatremia occurs during hospitalization for a Mamushi bite, cortisol measurement, hormone loading test, and head MRI should be performed to search for pituitary lesions because of the possibility of adrenal insufficiency caused by snake venom.