Effectiveness of tocilizumab monotherapy for IgG4-related disease-like features caused by idiopathic multicentric Castleman's disease: a case-based review.

Idiopathic multicentric Castleman's disease (iMCD) and immunoglobulin G4-related disease (IgG4-RD) are distinct systemic inflammatory diseases that can exhibit overlapping clinical manifestations, including elevated serum IgG4 levels and tissue infiltration of IgG4-positive plasma cells. Although interleukin-6 (IL-6) inhibitors are established first-line therapies for iMCD, optimal treatment strategies for cases of iMCD with IgG4-RD-like features remain unestablished, particularly regarding whether glucocorticoids are essential or not. Herein, we report our case of iMCD with IgG4-RD-like features successfully treated with tocilizumab monotherapy. A 68-year-old female presented with dyspnea due to a recurrent laryngeal tumor, accompanied by pulmonary consolidation, mediastinal and axillary lymphadenopathy, sclerosing mesenteritis, and retroperitoneal fibrosis. Laboratory evaluation revealed elevated C-reactive protein (CRP) and serum IgG4 levels. Although the organ involvement and elevated IgG4 levels were suggestive of IgG4-RD, and laryngeal and pulmonary specimens exhibited IgG4-positive plasma cell infiltration, histopathological examination of lymph node confirmed the diagnosis of iMCD; therefore, we diagnosed the patient with iMCD with IgG4-RD-like features. Tocilizumab monotherapy achieved rapid normalization of CRP and IgG4 levels, along with improvement of organ involvements. The patient attained long-term clinical remission without glucocorticoids. Our literature review identified 9 previously reported cases of iMCD with IgG4-RD-like features. Eight of nine cases showed an insufficient response to initial glucocorticoid monotherapy and subsequently required the addition of IL-6 targeting agents to obtain disease resolution. Together with the findings from our literature review, our case suggests that tocilizumab monotherapy may be a potential treatment option for IgG4-RD-like features caused by iMCD.