26-21: Paget Disease of Bone (Osteitis Deformans)

ESSENTIALS OF DIAGNOSIS

GENERAL CONSIDERATIONS

Paget disease of bone is manifested by one or more bony lesions having high bone turnover and disorganized osteoid formation. The involved bone first has increased osteoclast activity, causing lytic lesions that may progress at about 1 cm/year. Increased osteoblastic activity follows, producing a high rate of disorganized bone formation. Involved bones become vascular, weak, and deformed. Eventually, there is a final burned-out phase with markedly reduced bone cell activity and abnormal bones that may be enlarged with skeletal deformity.

The prevalence of Paget disease has declined by about 36% over the past 20 years. It is most common in the United Kingdom and in areas of European migration, and it is rare in Africa, India, Asia, and Scandinavia. In the United States, Paget disease affects about 1% of White persons over age 55 years, with its prevalence increasing with age over 40 years. Most cases are discovered incidentally during radiology imaging or because of incidentally discovered elevations in serum alkaline phosphatase.

Paget disease of bone may be due to a viral infection in genetically susceptible individuals, but the precise cause is unknown. About 20% of cases are familial and transmitted as an autosomal dominant trait with incomplete penetrance. Mutations in the SQSTM1 gene have been discovered in about 35% of patients with familial Paget disease and in 7% of patients with apparently sporadic Paget disease.

CLINICAL FINDINGS

A. Symptoms and Signs

Paget disease is often mild and asymptomatic. Only 27% of affected individuals are symptomatic at the time of diagnosis. Paget disease involves multiple bones (polyostotic) in 72% and only a single bone (monostotic) in 28%. It occurs most commonly in the pelvis, vertebrae, femur, humerus, and skull. The disease typically involves affected bones simultaneously and tends not to involve additional bones during its course. Pain, often described as aching, deep, and worse at night, is the usual initial symptom. It may occur in the involved bone or in an adjacent joint, which can be involved with degenerative arthritis. Paget disease typically affects long bones proximally and then advances distally, with bone pain at the osteolytic front being aggravated by weight bearing. Joint surfaces (such as the knee) can be involved and cause arthritic pain. The bones can become soft, leading to bowed tibias, kyphosis, and frequent “chalkstick” fractures with slight trauma. If the skull is involved, the patient may report headaches and an increased hat size; half such patients have dilated scalp veins, the “scalp vein sign.” Involvement of the petrous temporal bone frequently damages the cochlea, causing hearing loss (mixed ...