Paget’s disease (of bone) is of uncertain etiology . There is a monostotic and polyostotic (most common) form of the disease. Paget's disease is rare in patients under the age of 40 and uncommon in those between 40 to 55 years old. While the prevalence of disease in the US population is uncertain it is estimated to be at least 1% and increases with age. There is a slight male predominance. The disease is commonly asymptomatic and discovered incidentally on plain radiography done for other reasons. Symptoms however may occur due to a variety of reasons and depends to a large extent on the location of bony involvement and the activity of the disease. Bone pain is the most common complaint. Within the cranium and spinal regions symptoms due to nerve entrapment may prompt the patient to seek medical care. It is noteworthy that active Pagetic bone is hyperemic to the extent that patients may present with congestive heart failure when there is extensive involvement. It follows that the active lesions are "3 phase positive" on bone scanning.

General distribution of disease:
-pelvis 30-75%
-sacrum 30-60%
-spine 30-75% (mostly lumbar)
-skull 25-65%
-proximal long bones 25-35% (especially femur)
-other sites: proximal humerus, scapula, and clavicle

There are 3 well described stages of Paget’s disease although all 3 phases may coexist in a single bone at the same time. In general the disease progresses from a "lytic" to a mixed "lytic/sclerotic " and finally a "sclerotic " stage. The radiographic findings mirrors the underlying pathophysiologic process affecting osteoclasts and osteoblasts residing in the involved bone at the time of imaging.

While the radiographic findings vary with the stage of disease several characteristic lesions are worth noting as these have some increased specificity for Paget's. "Osteoporosis circumscripta" is a geographic lucent zone with sharply defined borders between lucent bone and normal bone usually identified in the cranium. As the disease progresses the bone becomes increasingly sclerotic, thickened and develops a “cotton wool” appearance. The “blade of grass” lesion, seen in long bones, appears as a distinct "V" shaped demarcation between healthy and Pagetic bone. The "brim sign" is radiographically apparent thickening of the ileopectineal line. Vertebral involvement causes a thickening of the vertebral body with peripheral sclerosis or “picture-framing.” The “ivory body” is a radiologic term used to describe an entirely sclerotic vertebral body.

Complications from Paget’s disease:

-neoplasms associated with Paget’s disease are sarcomatous degeneration and giant cell tumors
-deformity of bone, fracture, or neurologic compromise secondary to bone expansion and compression of neurologic structures (cord, nerve roots, cranial nerves)
-hypercalcemia especially in immobilized patients.

-arthridities:

crystalline deposition (gout, CPPD), rheumatoid, ankylosing spondylitis, degenerative joint disease


Finally it is important to note that in patients with stable disease, significant changes in biochemical markers or symptoms should prompt oncologically focused radiographic evaluation. Late stage fractures should be considered to be pathologic until proven otherwise.

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