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Masked Diabetes Insipidus Hidden by Severe Hyponatremia: A Case of Pituitary Metastasis of Lung Adenocarcinoma

Miki Watanabe, Junichi Yasuda, Kenji Ashida, Yuko Matsuo, Ayako Nagayama, Yuka Goto, Shimpei Iwata, Masayuki Watanabe, Jun Sasaki, Tomoaki Hoshino, Masatoshi Nomura

(Division of Endocrinology and Metabolism, Department of Internal Medicine, Kurume University School of Medicine, Kurume, Fukuoka, Japan)

Am J Case Rep 2020; 21:e928113

DOI: 10.12659/AJCR.928113

BACKGROUND: Hyponatremia is an electrolyte disorder frequently encountered by clinicians. Secondary adrenal insufficiency due to pituitary metastatic tumors should be considered as an alternative diagnosis when clinicians encounter patients with lung cancer who demonstrate hyponatremia. However, masked central diabetes insipidus should also be considered to prevent critical dehydration when glucocorticoid replacement therapy will be initiated.
CASE REPORT: A 70-year-old man with advanced lung adenocarcinoma demonstrated high-grade hyponatremia of 122 mmol/L. Magnetic resonance imaging disclosed a metastatic pituitary tumor and endocrinological examinations confirmed panhypopituitarism, including secondary adrenal insufficiency. Hydrocortisone replacement revealed masked diabetes insipidus with elevation of serum sodium levels that reached 151 mmol/L. Desmopressin administration was required to prevent water depletion and to immediately ameliorate the hypernatremia.
CONCLUSIONS: This is the first case report of masked diabetes insipidus that demonstrated high-grade hyponatremia. Secondary adrenal insufficiency can mask the hypernatremia that is a typical manifestation of diabetes insipidus. Physicians should consider adrenal insufficiency and diabetes insipidus due to pituitary metastasis of advanced malignancies, even when they encounter patients with hyponatremia.

Keywords: Diabetes insipidus, adrenal insufficiency, Glucocorticoids, Hyponatremia, Lung Neoplasms, Pituitary Neoplasms

This paper has been published under Creative Common Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0) allowing to download articles and share them with others as long as they credit the authors and the publisher, but without permission to change them in any way or use them commercially.
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