EP1129 - ECE_1352 - Anti-rabphilin-3A antibody–positive arginine vasopressin deficiency after COVID-19 infection and vaccination: evidence for autoimmune hypothalamic–neurohypophyseal inflammation

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Abstract Background Arginine vasopressin deficiency (AVP-D) has been increasingly reported after coronavirus disease 2019 (COVID-19) infection and SARS-CoV-2 vaccination. However, most published cases have been described as idiopathic or post-infectious, and the underlying etiology remains largely unresolved. Anti-rabphilin-3A antibodies have recently been identified as a highly sensitive and specific biomarker for lymphocytic infundibulo-neurohypophysitis (LINH), an autoimmune inflammatory disorder of the hypothalamic–neurohypophyseal system. Aim To present two anti-rabphilin-3A antibody–positive cases of COVID-19–associated AVP-D and to re-evaluate previously reported cases. Case presentations We describe two patients who developed new-onset AVP-D following COVID-19–related events. One patient developed abrupt polyuria and polydipsia approximately three weeks after SARS-CoV-2 infection, while the other developed progressive AVP-D several weeks after SARS-CoV-2 vaccination following prior infection. Endocrinological evaluation in both cases demonstrated hypotonic polyuria with inappropriately low plasma AVP levels, blunted AVP responses to hypertonic saline, and preserved responsiveness to desmopressin. Pituitary magnetic resonance imaging showed loss of the posterior pituitary bright spot with pituitary stalk thickening. During follow-up, pituitary stalk swelling markedly improved within one month in the post-infection case, whereas persistent stalk enlargement was observed for more than one year in the post-vaccination case. Serum anti-rabphilin-3A antibodies were detected in both patients, strongly supporting a diagnosis of LINH and allowing avoidance of invasive pituitary biopsy. Review of the literature A review of previously reported COVID-19–associated AVP-D cases suggests that pituitary stalk swelling is observed more frequently after vaccination than after infection, whereas immunological evaluation has rarely been performed in either setting. This pattern is consistent with our longitudinal imaging findings, indicating potential differences in disease course depending on the triggering event. No established diagnostic biomarkers have been applied in most cases, leaving the etiology undefined. Additional evidence We have also recently reported a pediatric case of post-COVID-19 AVP-D with positive anti-rabphilin-3A antibodies, supporting autoimmune involvement across age groups. Conclusions Our findings provide immunological evidence that a subset of COVID-19–associated AVP-D represents autoimmune hypothalamic–neurohypophyseal inflammation. Anti-rabphilin-3A antibody positivity may serve as a non-invasive biomarker indicating autoimmune involvement and could aid etiological classification and avoidance of invasive diagnostic procedures in patients with AVP-D occurring after COVID-19 infection or vaccination. Although all COVID-19–associated AVP-D cases experienced at our institutions to date have been antibody-positive, further case accumulation is required to evaluate diagnostic sensitivity and to clarify differences between antibody-positive and -negative AVP-D.

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