Non-IgG4-related Multifocal Fibrosclerosis.

Multifocal fibrosclerosis (MFS), which causes systemic and chronic connective tissue inflammation, has been associated with IgG4 and regarded as an identical entity with "IgG4-related disease (IgG4-RD)". Although a few cases of MFS mimicking IgG4-RD histopathologically, despite the absence of a serum IgG4 elevation and IgG4-positive plasma cell infiltration, have been reported, there is, so far, little information regarding such exceptional cases. We herein demonstrate a case of non-IgG4-related MFS presenting with periaortitis and parotiditis, whose histological findings were consistent with IgG4-RD despite the absence of elevated serum and tissue IgG4 levels.