Idiopathic multicentric Castleman disease in a patient with an IgG4-related disease phenotype.

In this article, we report a case of idiopathic multicentric Castleman disease (iMCD) with an atypical manifestation in a man in his early 50s, whose first symptoms included recurrent episodes of pancreatitis, retroperitoneal fibrosis and lymphadenopathy. These features are more commonly associated with IgG4-related disease (IgG4-RD). Although clinical findings were suggestive of IgG4-RD, IgG4 levels were within the normal range, along with a histopathological examination, ultimately leading to an iMCD diagnosis, showing characteristic vascular hyperplasia and a polyclonal plasma cell infiltrate showing no signs of IgG4+ plasma cells. In addition, the patient showed improvement with siltuximab, an interleukin-6 inhibitor drug specific for iMCD. This challenging case enhances the importance of combining clinical evaluation, serological testing and histopathological analysis to establish a definitive diagnosis.