ACR Codes: 4.7
Paget disease (osteitis deformans) is a condition of unknown cause affecting approximately 3 per cent of the population over age 40 years. Paget disease appears to be particularly common in Australia, Great Britain and certain areas of Europe.The disease is characterized excessive and abnormal remodeling of bone. The process of osseous resorption produces a diagnostic radiographic appearance of coarsened trabeculae.
In many patients, the disorder is diagnosed as an incidental finding. Other times, the disease is manifested initially with an enlarging head size , severe kyphosis and bowing of the long bones. It can also present with pathologic fracture or neurologic deficits with vertebral compression fractures. Congestive heart failure has been seen because of hyperemia in pagetic bone. Urinary hydroxyproline and elevation in serum alkaline phosphatase and hydroxyproline are laboratory indicators.
Paget disease predominates in the axial skeleton, especially in the pelvis (30-75 percent), sacrum, cranium and proximal femur. In the skull, pagetic changes range from osteolysis (osteroporosis circumscripta) to focal radiodense areas ("cotton wool”) patches. Basilar invagination, seen in up to 1/3 of patients, is characterized by upward protrusion of the foramen magnum and surrounding bone. Paget disease frequently involves the vertebral column and complications include vertebral body collapse, spinal canal stenosis, neural foraminal stenosis and “steal” phenomenon from the spinal cord as result of increased flow in pagetic bone. Before advanced disease, the vertebral bodies may exhibit enlargement and coarsened trabeculae and “picture frame” appearance from condensation of bone in along the periphery of the vertebral body. In the pelvis, manifestations include trabecular thickening and areas of bone resorption seen as lyric areas. In the long bones, most common the femur, tibia and humerus, the findings are characterized by epiphyseal involvement with an advancing wedge or flame-shaped edge with widening and deformity of the affected bone.Bone scintigraphy demonstrates areas of increased radiotracer uptake in affected areas. Scintigraphic abnormalities may precede radiographic changes. Serial bone scans may also provide objective evidence of effects of therapy.
Complications include insufficiency (stress) fractures and sarcomatous degeneration. Cortical stress fractures appear as horizontal radiolucent areas with predilection for convex aspect of the bone (lateral femoral neck, anterior tibia). Neoplastic involvement with sarcomatous degeneration occurs in up to 10 percent of cases. The bones most commonly affected are the femur, pelvis and the humerus. Osterosarcoma (50 %) and fibrosarcoma (25%) predominate. Giant cell tumors may be associated with Paget disease and are almost always confined to the skull or facial bones.
Since the 1950s, effective therapeutic agents have been used. Calcitonin, a potent inhibitor of bone resorption, can lead to pain relief within weeks and a reduction in serum alkaline phosphatase. Disodium etidronate also has been used to inhibit bone resorption by binding to hydroxyapatite crystals. Mithramycin is an antibiotic that has been used successfully in the treatment of Paget disease.
EDITOR'S NOTE: The initial phase of the disease characterized by rapid bone resorption, and the intermediate phase with markedly increased osteoblastic activity both demonstrate very intensely increased accumulation on the delayed phase of bone scans. Osteoporosis circumscripta typically demonstrates a rim of increased activity bordering the lesion. When active remodeling slows or ends, the "third", "late" or "cold" phase begins. Tracer accumulation on the bone scan during this phase is variable. Individual involved bones can simultaneously present more than one stage of the disease process, reflecting variation of the duration of Paget disease at different sites in the bone.
References:
"The Pathophysiological Basis of Nuclear Medicine" by A. Elgazzar and "An Atlas of Planar and SPECT Bone Scans" by Holder, Fogelman and Collier.
Reference(s): 1) Resnick DR. Bone and Joint Imagiong, 2nd Ed. Philadelphia. W.B. Saunders, 1996.
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Disease Topic 3596 
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