Primary intraosseous Rosai-Dorfman disease: Clinicopathological features and an assessment of a possible relationship with IgG4-related disease.

Rosai-Dorfman disease (RDD) is a rare proliferative disorder of histiocytes, and primary solitary RDD of the bone is extremely rare. Some RDDs exhibit increased immunoglobulin (Ig)G4 positive (IgG4+) plasma cell infiltration and the histopathological features of IgG4-related disease (IgG4-RD). However, the association between RDD and IgG4-RD remains unclear. Therefore, this study aimed to investigate the relationship between primary intraosseous RDD and IgG4-RD. We collected data on 11 primary intraosseous Rosai-Dorfman diseases to summarize their clinicopathological features and to investigate their relationship with IgG4-RD. The most common sites were the long bones, followed by the vertebrae. The age of onset was higher in our Chinese cohort as compared with Western patients reported in the literature, with an average age of 39.2 and a median age of 34 years. Sclerosis was present in seven cases and storiform arrangement was observed in only one case. Obliterative phlebitis was not observed in any patient. The number of IgG4+ plasma cells ranged from 5 to 50 cells per high-power field, with IgG4/IgG ratios ranging from 5 to 25 %. Primary intraosseous RDD may show fibrosis and increased IgG4+ plasma cell infiltration, but does not meet the criteria for IgG4-RD. We concluded that RDD did not belong to the IgG4-RD spectrum.