I write with regard to the paper by Zuber and colleagues that purports to demonstrate a case of pigmented villonodular synovitis (PVNS).1

The pathology material presented by the authors, however, is not diagnostic of PVNS, in that the cellular infiltrate did not demonstrate the large polyhedral cells—usually dubbed histiocytes—that are requisite for the diagnosis of PVNS. Villi, nodules, giant cells, and haemosiderin are not specific, and may be seen in a variety of conditions other than PVNS. It is the histiocyte that renders the pathology of PVNS unique and diagnostic. Indeed, Lichtenstein has described PVNS as a ‘histiocytosis’ of the synovial membrane.2

In addition, the authors suggest that in their patient PVNS was found to affect the second to fifth MCP joints. However, the diffuse form of PVNS is nearly always monarticular; documented cases …