To describe a novel association between myelin oligodendrocyte glycoprotein antibody–associated disease (MOGAD) and unicentric hyaline vascular Castleman disease (UCD-HV), and to propose a potential immunopathogenic link.

MOGAD is an autoimmune demyelinating disorder mediated by MOG-IgG1 antibodies. The mechanisms underlying autoreactive antibody generation remain incompletely understood. UCD-HV is a lymphoproliferative disorder characterized by follicular dendritic cell (FDC) dysplasia and altered germinal center signaling, which may promote autoreactive B-cell survival.

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A 26-year-old postpartum woman presented with longitudinally extensive transverse myelitis, diplopia, and urinary retention. MRI demonstrated thoracic cord demyelination and brain lesions involving the splenium and pons. CSF showed lymphocytic pleocytosis and elevated protein. Serum testing was positive for MOG-IgG, confirming MOGAD. During paraneoplastic evaluation, imaging revealed left axillary lymphadenopathy. Excisional biopsy demonstrated features consistent with unicentric hyaline vascular Castleman disease, including regressed germinal centers, “onion-skin” mantle zones, and lollipop vascular structures.

The patient was treated with high-dose corticosteroids and plasma exchange, resulting in marked neurologic improvement. Surgical resection of the involved lymph node was performed five months later. Following resection, the patient experienced sustained clinical remission with decreasing MOG antibody titers and no relapses over two years of follow-up.

This case suggests a potential pathogenic link between UCD-HV and MOGAD. Dysregulated germinal center activity in Castleman disease may promote autoreactive B-cell activation and MOG-IgG1 production. Surgical resection of the affected lymph node may eliminate a source of aberrant immune signaling, contributing to sustained remission. Further studies are needed to evaluate this association and its therapeutic implications.