Tartrate-resistant acid phosphatase containing cells in nodular fasciitis, proliferative fasciitis, and proliferative myositis.

Five cases of nodular fasciitis, three cases of proliferative fasciitis, and one case of proliferative myositis were investigated by tartrate-resistant acid phosphatase (TRAP) histochemistry on conventional paraffin-embedded material. In all cases varying numbers of enzyme-positive cells were detected. Cytological investigations revealed the presence of small round cells, elongated spindle cells, medium-sized mono- or binucleated cells, and multinuclear giant cells, the latter resembling osteoclasts. However, the typical ganglion-like cells were TRAP-negative in almost all tests. The TRAP-pattern may help to differentiate nodular fasciitis and allied lesions from inflammatory pseudotumours or organising haematomas, as the latter do not contain TRAP-positive cells. As TRAP appears to be a marker for a special population of phagocytizing and non phagocytizing histiocytes, nodular fasciitis and its proliferative variants may be assumed to be fibrohistiocytic tumorous conditions.