Arginine vasopressin deficiency in primary Sjögren’s syndrome: a case report and literature review

Background Arginine vasopressin deficiency (AVP-D) is rarely been reported in primary Sjögren’s syndrome (pSS) and may be overlooked because excessive fluid intake can be attributed to xerostomia. Case presentation A 45-year-old woman presented with xerostomia, polydipsia, polyuria, and nocturia, with a 24-h urine output of 4.4 L. Serum sodium reached 158 mmol/L, with marked plasma–urine osmotic dissociation (plasma osmolality 318, urine osmolality 115 mOsm/kg H 2 O). pSS was diagnosed on the basis of anti-SSA positivity, objective exocrine-gland dysfunction, and focal lymphocytic infiltration on labial salivary gland biopsy with one focus containing more than 50 lymphocytes per 4 mm 2 of glandular tissue (focus score: 1 focus/4 mm 2 ). During supervised water deprivation, serum sodium rose from 148.4 to 154.3 mmol/L, prompting termination at 6 hours in the setting of intolerable thirst and discomfort. Urine osmolality was 292 mOsm/kg H 2 O despite plasma osmolality of 326 mOsm/kg H 2 O; after posterior pituitary injection (5 U), it increased to 441 mOsm/kg H 2 O (+51.0%). These findings supported the diagnosis of AVP-D. Unenhanced MRI showed a partial empty sella with pituitary flattening, without stalk thickening or a sellar/suprasellar mass; the posterior-pituitary bright spot could not be reliably assessed because of anatomical distortion. Desmopressin promptly relieved thirst and polyuria. Given suspected autoimmune hypothalamic–neurohypophyseal involvement, glucocorticoids and mycophenolate mofetil were added. At approximately 1 year, serum sodium was normal and urine output was approximately 2.0 L/day, with desmopressin continued. Conclusion This case highlights the occurrence of AVP-D in association with pSS, with possible autoimmune hypothalamic-neurohypophyseal involvement. Although the underlying mechanism remains uncertain, disproportionate polyuria and nocturia in patients with pSS, particularly in the presence of hypernatremia, should prompt evaluation for AVP-D rather than being attributed solely to sicca symptoms.