Idiopathic multiple castleman disease case combined with severe neuropathy, Sjogren's syndrome and membrane nephropathy treated by rituximab: a case report and literature review.

Background: Idiopathic multicentric Castleman disease (iMCD) is a lymphoproliferative disorder characterized by dysregulated systemic immunity. Multiple cytokines had been found involved in the disease pathogenesis. Hence, involvement of multiple systems in iMCD complicates diagnosis and efficacy assessments. Although guidelines recommend anti-interleukin-6 (IL-6) agents as the primary treatment, options for second-line therapy remain indeterminate. Case presentation: A 65-year-old woman presented with progressive polyneuropathy and nephrotic-range proteinuria ten days after COVID-19 vaccination. Evaluation revealed multicentric lymphadenopathy, elevated IL-6, and plasmacytic-variant CD histopathology (HHV-8 negative). Concurrent Sjögren's syndrome and anti-PLA2R-negative membranous nephropathy were confirmed. After exclusion of POEMS syndrome, iMCD-NOS with intermediate severity was diagnosed. Initial rituximab-cyclophosphamide-dexamethasone therapy resulted in paradoxical neurological worsening despite declining VEGF levels. Anti-IL-6 therapy was inaccessible due to economic constraints. Single-agent rituximab was initiated and continued for nine cycles over 24 months, achieving clinical remission by January 2024 with near-normalization of inflammatory markers, resolution of proteinuria, and neurological recovery. Conclusions: This case demonstrates that rituximab monotherapy can achieve clinical remission in iMCD-NOS with concurrent autoimmune manifestations when anti-IL-6 therapy is unavailable. The delayed response pattern-with biomarker improvement preceding clinical recovery-highlights the importance of serial VEGF monitoring and persistence with B-cell-directed therapy before concluding treatment failure.