Pigmented villonodular synovitis associated with psoriatic polyarthropathy: and electron microscopic and immunocytochemical study.

A case of pigmented villonodular synovitis in a patient with psoriatic polyarthropathy was studied by means of light microscopy, electron microscopy and immunocytochemical techniques. The lesion consisted of mononuclear phagocytes with features intermediate between type A and type B cells, two types of multinucleate giant cells, an abnormal vasculature, extravasated fibrin and erythrocytes. An unexpected feature was the presence of a mononuclear cell whose cytoplasm contained intermediate filaments and reacted strongly to antisera to cytokeratins. Such a cell type has not previously been described in this condition and its significance is unclear. The findings support the theory that the pathogenesis of PVNS involves leakage of blood through abnormal vessels resulting in the local accumulation and proliferation of mononuclear phagocytes, connective tissue cells and unidentified cytokeratin positive mononuclear cells. The aetiology of the vascular damage, however, remains unknown.