Paget’s disease most commonly occurs in England, Australia, New Zealand, Scandanavia, Canada and the northern U.S. The average age of onset is between 50 and 55 years. It is twice as common in men as women. The cause is unknown. Pathologically, it is characterized by destruction of bone (lysis) followed by attempts at repair (blastic) which are often disorganized.

Paget’s disease may affect any bone in the body. It may affect a single bone and never extend to others, or it may spread. In order of frequency, the following bones are affected: pelvis, vertebrae, femur, skull, tibia, clavicle, humerus, ribs, and rarely the sternum, calcaneous, talus, phalanges, metatarsals, mandible, patella, and other sesamoid bones. Only 20% of the patients are symptomatic, usually complaining of ill-defined pain at the site. Characteristically, there is an elevation of alkaline phosphatase (15-20x normal). Serum calcium and phosphorous are usually normal, but serum calcium may be elevated in an immobilized patient.

The radiographic appearance is dependent on the phase of the disease: lytic, reparative or mixed. The principle radiographic findings are thickening of the cortex, coarsening of the trabeculae, enlargement of bone, areas of lucency, pathces of dense bone described as “cotton wool” or “cotton ball,” and evidence of bone softening. In the long bone, the process almost always involves the end of the bone extending into the diaphysis. In the pelvis, it usually involves some portion of the acetabulum. Healing of the lytic phase has been described as a result of treatment with diphosphonates and calcitonin.

Pagetic bone takes up all radionuclide bone scanning agents avidly. The diagnosis of Pagets’s disease can be made on the basis of a bone scan because of thie intense activity and the pattern of bone involvement (the end of the bone with variable extension into the shaft and often evidence of softening manifested by bowing of the long bones and flattening of vertebrae. CT images mirror the findings on plain film radiography: cortical thickening, coarsening of the trabeculae, and focal sclerotic densities in intramedullary bone (“cotton balls”). The osteolytic phase demonstrates considerable thinning of the cortex of long bones and tables of the skull. The classic expression of the lytic phase in the skull is known as osteoporosis circumscripta. During the reparative stage, the skull becomes markedly thickened with a coarsened inner and outer table and widened diploic space.