SAT-076 - Long-Term compensated and intermittent arginine vasopressin deficiency following pituitary stalk germinoma

Background

Arginine vasopressin deficiency (AVP-D), formerly central diabetes insipidus, is a common manifestation of hypothalamic–pituitary dysfunction in suprasellar germinomas and is generally considered permanent. Long-term evolution of AVP-D following treatment remains incompletely characterized, particularly long-term compensated and intermittent phenotypes.

Clinical Case

A previously healthy female developed progressive polyuria and polydipsia beginning at age 5, progressing to nocturia 4–5 times nightly by age 10. Laboratory evaluation demonstrated hypernatremia (Na 144–147 mmol/L), and water deprivation testing confirmed AVP-D. Growth hormone deficiency was diagnosed, with a peak GH of 3.7 ng/mL. MRI revealed pituitary stalk thickening with heterogeneous enhancement and loss of the posterior pituitary bright spot. Serial imaging demonstrated progression to a 2.4 cm suprasellar mass with an associated mass effect and surrounding edema involving the optic pathways and adjacent deep brain structures, and biopsy confirmed germinoma. Following proton radiation therapy (total 4500 cGy), MRI demonstrated complete radiographic resolution with no residual mass effect. During adolescence, desmopressin was discontinued with normalization of serum sodium (140–142 mmol/L) and absence of symptoms, consistent with a compensated phase.

In adulthood, the patient remained asymptomatic; however, laboratory evaluation demonstrated persistently low urine osmolality (66–181 mOsm/kg) and low urine specific gravity (1.002–1.004), indicating impaired urinary concentrating ability. At age 23, during acute illness, she developed hypernatremia (Na 146–152 mmol/L), requiring a single dose of desmopressin, with subsequent normalization. No maintenance therapy was required thereafter.

Conclusion

This case demonstrates a three-phase evolution of AVP-D following pituitary stalk germinoma: overt deficiency, compensated phase, and intermittent recurrence under physiological stress. Persistent biochemical abnormalities despite clinical remission support partial vasopressin deficiency with intact thirst-mediated compensation. These findings support that even in the setting of prior structural and compressive hypothalamic–pituitary injury, AVP-D may evolve along a dynamic continuum rather than a fixed, irreversible deficit. This has important clinical implications, as patients with apparent remission may remain at risk for recurrence during physiological stress and require long-term monitoring and anticipatory guidance.

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