When idiopathic retroperitoneal fibrosis mimics Castleman disease: a challenging differential diagnosis

Idiopathic retroperitoneal fibrosis (I-RPF) can occur either in the spectrum of IgG4-related disease or as a non-IgG4-related form. I-RPF, especially the IgG4-related forms, can sometimes mimic clinically and/or histologically Castleman disease; to the best of our knowledge, this is the first case of non-IgG4 I-RPF with Castleman-like features described in the literature. In this scenario, differentiating I-RPF and Castleman disease can be difficult, and additional serum data such as C reactive protein, interleukin-6 and platelet count are needed.