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Persistent SIADH-like Hyponatremia Requiring Tolvaptan Despite Glucocorticoid Replacement in Rathke’s Cleft Cyst-Associated Hypophysitis: A Therapeutic Dilemma

Year: 2026

Type: article

Abstract: A 52-year-old man presented with severe hyponatremia and Rathke's cleft cyst (RCC)-associated hypophysitis with enlargement of the pituitary stalk. Hyponatremia persisted despite treatment with high-dose hydrocortisone, hypertonic saline, and loop diuretics, ultimately requiring low-dose tolvaptan. Hyponatremia associated with RCC is usually attributed to secondary adrenal insufficiency (SAI), in which glucocorticoid replacement generally restores free water excretion but may unmask arginine vasopressin deficiency (AVP-D). In the present case, however, persistent AVP-mediated water retention beyond SAI appeared to predominate, suggesting AVP dysregulation associated with inflammatory pituitary involvement. This case highlights the therapeutic dilemma of balancing masked AVP-D against persistent AVP excess in hyponatremia associated with RCC.

Source: Internal Medicine

DOI: 10.2169/internalmedicine.7951-26

Authors: Yuya Shimizu, Reo Ishii, Kazumasa Tanaka, Koki Kinoshita, Jun Toyama, Noriaki Fukuhara, Masahiro Nezu

Institutions: Yamanashi Prefectural Central Hospital, Toranomon Hospital, Tohoku University

Language: English

Topic: Electrolyte and hormonal disorders

Subfield: Nephrology

Field: Medicine

Domain: Health Sciences

SDG: Good health and well-being

Open Access status: diamond

OpenAlex ID: W7221053895

FWCI:

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