Particle disease: cytopathologic findings of an unusual case.

Particle disease is a rare lesion that results from an inflammatory response due to wear debris-induced osteolysis following arthroplasty. Particles resulting from the wear debris cause macrophage activation and phagocytosis. Particle disease often leads to joint loosening and implant failure. Radiologically, it often results in a well-defined osteolytic lesion-mimicking tumor. A 68-year-old man who presented with chronic hip pain following total hip replacement was studied by fine-needle aspiration. An ultrasound-guided aspiration revealed hypercellular smears consisting predominantly of proliferating mesenchymal cells, foamy macrophages, inflammatory cells, and background acellular debris. Numerous multinucleated giant cells were observed as well. Differential diagnosis includes primary or metastatic clear-cell tumors.