Pseudosarcoma in Paget's disease.

The authors describe the case of a male patient who had had Paget's disease since 1973 which led to the diffuse swelling of the proximal femur in 1993. The elevated alkaline phosphatase level and the destructive lytic lesions on the X-ray of the femur raised the possibility of malignancy. The bone scan showed increased accumulation in the proximal part of the left femur. On the MR the low T1 and the elevated T2 signal intensity suggested malignity despite that in some regions signals typical of adipose tissue could also be seen, which is usually interpreted as a sign of benignity. In the histological specimens no signs of malignant tumour cells were identified. The patient received bisphosphonate treatment which decreased his pain and swelling and also the alkaline phosphatase level. The patient died because of a rapidly progressing retroperitoneal fibrosarcoma and lung metastasis in 1996. The autopsy did not prove any malignant transformation of Paget's disease of bone in the proximal femur.