#3-35E. Unmasking the Great Mimic: Navigating the New iMCD Subtypes (Arthritis Rheumatol, 2025)

Have you ever encountered a patient with unexplained lymphadenopathy and systemic inflammation that defies standard autoimmune diagnoses? In this expert perspective, Chen and colleagues delineate the updated classification of idiopathic multicentric Castleman disease (iMCD) into three distinct subtypes: TAFRO, IPL, and NOS. A critical evolution in this framework is the formal characterization of iMCD-IPL (idiopathic plasmacytic lymphadenopathy), a subtype presenting with polyclonal hypergammaglobulinemia that frequently mimics IgG4-related disease due to elevated serum IgG4. Crucially, the authors suggest that while iMCD-IPL shares features with IgG4-RD, the presence of significant systemic inflammation (fever, high CRP) distinguishes the former. However, clinicians must exercise caution when interpreting biopsies; the authors emphasize that histopathologic features like hypervascularity and plasmacytosis are non-specific and can appear in various reactive conditions. Consequently, the study argues that diagnosis demands rigorous correlation between clinical phenotypes and pathology rather than reliance on histology alone5. This review is vital for rheumatologists to prevent misdiagnosis of these "great mimics" and ensures patients receive appropriate targeted therapies like IL-6 inhibitors rather than ineffective treatments.

Citation: Chen, L.Y.C., Zhang, L. and Fajgenbaum, D.C. Expert Perspective: Diagnosis and Treatment of Castleman Disease. Arthritis & Rheumatology. 2025. DOI: 10.1002/art.43269

Disclaimer: This audio summary is based on personal interpretation and does not guarantee the exact content of the original paper. Please refer to the original article for details.