Paget's disease

(Sir James Paget, 1814 -1899, English surgeon), an osteitis deformans of unknown cause characterized by excessive and abnormal bone remodelling. Active pagetic bone is characterized by the presence of giant osteoclasts containing large numbers of nuclei and intranuclear inclusion bodies. The radiographic features of this disease are virtually diagnostic; an initial osteolytic phase occurs, most noteable in the skull and tubular bones, with a subsequent osteosclerotic phase, particularly evident in the axial skeleton (Fig.1 and Fig.2). In the skull, the initial osteolytic changes in the skull are termed osteoporosis circumscripta. Later bone tissue that is formed is abnormal architecturally, consisting of primitive or woven bone with increased vascularity and a pronounced connective tissue reaction. Bones are enlarged and show increased radiodensity and accentuated trabecular pattern. (Also, calcaneus (III:1), Fig. 2.) Characteristic radiographic signs include the cotton wool appearance of the cranial vault and the picture frame vertebral body (Fig.3) (Fig.4). Skeletal deformities include kyphosis and bowing of the long bones of the extremities. Bone involvement may lead to pathologic fracture.

Scintigraphy is valuable in the diagnosis of Paget's disease, as areas of skeletal involvement show increased uptake of bone-seeking radiotracers and sometimes marrow replacement. These changes sometimes precede radiographic changes. Scintigraphy can also document the extent of the initial lytic phase of Paget's disease, and serial bone scintigraphs may provide help in determining the effectiveness of various therapeutic agents.

Although CT scanning is generally not required, it may be of value in the further delineation of a number of complications of Paget's disease.

MR imaging best reveals alterations in patients with long-standing inactive phases of Paget's disease, such as cortical thickening, coarse trabeculation, enlargement of the bone, reduction in the size of the medullary cavity and bowing of tubular bones. In the active stage the MR imaging findings are variable. In this stage, the haematopoietic marrow is replaced by fibrous connective tissue with large vascular channels, accounting for the MR imaging features, which may simulate those of tumour or infection. On spin-echo images, the signal intensity of the involved bone marrow may be decreased on the T1-weighted sequences and increased on the T2-weighted sequences.

Complications associated with Paget's disease include insufficiency fractures, neurologic symptoms and signs, skeletal deformities, neoplasms and joint alterations. Neoplastic involvement in Paget's disease includes malignant degeneration, giant cell tumour and superimposition of another tumourous condition, such as metastatic disease, plasma cell myeloma and lymphoma. Osteosarcoma and fibrosarcoma are most common, although chondrosarcoma may also be found. Bone destruction, a soft tissue mass, cortical disruption, bone spiculation and a persistent fracture without evidence of healing are typical in patients with sarcomatous degeneration (Fig.5). Giant cell tumours associated with Paget's disease are almost always confined to regions of the skeleton involved in the pagetic process, such as the skull or the facial bones. A lytic, expansile lesion with a soft tissue mass is observed.

Among the articular abnormalities in Paget's disease are deposition of monosodium urate and calcium pyrophosphate dihydrate crystal deposition disease and osteoarthritis.

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