Use of tocilizumab to treat IgA nephropathy complicated by idiopathic multicentric Castleman disease: a case report.

BACKGROUND: Idiopathic multicentric Castleman disease (iMCD) is a rare polyclonal lymphoproliferative disorder characterised by excessive interleukin-6 (IL-6) production. Interleukin-6 is known to enhance the synthesis of galactose-deficient IgA1 (Gd-IgA1), contributing to the pathogenesis of IgA nephropathy (IgAN). Additionally, vascular endothelial growth factor (VEGF) is also upregulated by IL-6, further exacerbating glomerular injury. Tocilizumab (TCZ), an anti–IL-6 receptor antibody, has been shown to inhibit IL-6 signaling, potentially reducing Gd-IgA1 and VEGF levels. Here, we report a rare and unique case of IgAN associated with iMCD, in which renal function, urinary protein levels, and serological markers improved following the administration of TCZ. CASE PRESENTATION: A 35-year-old male initially presented with proteinuria and haematuria and was later diagnosed with iMCD through lymph node biopsy. A renal biopsy revealed features consistent with IgAN, including mesangial IgA and C3 deposition. Tocilizumab was initiated at a dose of 8 mg/kg biweekly. Following treatment, improvements were observed in serum creatinine (from 1.45 to 1.23 mg/dL) and proteinuria (from 1.18 to 0.17 g/day). Following TCZ administration, serum VEGF levels decreased from 1557 to 702 pg/mL, and Gd-IgA1 levels declined from 14.99 to 5.97 ng/mL, indicating that TCZ may have contributed to the suppression of disease activity. CONCLUSION: This case highlights the potential role of IL-6 inhibition in managing renal involvement in iMCD, particularly in cases complicated by IgAN. The reduction in serum Gd-IgA1 and VEGF levels following TCZ administration suggests a possible mechanism for renal protection. This report contributes valuable insights into treatment strategies for IgAN associated with iMCD and underscores the importance of considering IL-6–targeted therapy in similar cases.