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Key Features

Essentials of Diagnosis

  • Often asymptomatic

  • Bone pain may be first symptom

  • Kyphosis, bowed tibias, large head, deafness

  • Frequent fractures

  • Serum calcium and phosphate normal; alkaline phosphatase elevated; urinary hydroxyproline elevated

  • Dense, expanded bones on radiograph

General Considerations

  • Common condition manifested by one or more bony lesions having high bone turnover and disorganized osteoid formation

  • Involved bones

    • Have increased osteoclast activity, causing lytic lesions in bone that may progress at about 1 cm/yr

    • Increased osteoblastic activity follows, producing a high rate of disorganized bone formation

    • Become vascular, weak, and deformed

    • Eventually, there appears to be a final burned-out phase with markedly reduced bone cell activity and abnormal bones that may be enlarged with skeletal deformity

  • Most often discovered incidentally during radiographic imaging or evaluation of serum alkaline phosphatase elevation

  • Cause is unknown; about 20% of cases are familial and transmitted as an autosomal dominant trait with incomplete penetrance

Demographics

  • Most common in the United Kingdom and in areas of European migration, particularly New Zealand, Australia, the United States, South Africa, Quebec, and Brazil

  • It is uncommon in Africa, Asia, and Scandinavia

  • Affects 3% of whites over age 55 years; prevalence increases with age

Clinical Findings

Symptoms and Signs

  • Often mild and asymptomatic; only 27% symptomatic at diagnosis

  • Involves multiple bones (polyostotic) in 72% and only a single bone (monostotic) in 28%, occurring most commonly in the pelvis, vertebrae, femur, humerus, and skull

  • Pain is usual first symptom

    • Usually described as aching and deep

    • Often worse at night

  • Bones become soft, leading to bowed tibias, kyphosis, and frequent fractures with slight trauma

  • If skull is involved, patient may report headaches, increased hat size, and deafness

  • Increased vascularity over involved bones causes increased warmth

  • Sarcomatous change suggested by marked increase in bone pain

Differential Diagnosis

  • Bone tumor, eg, osteosarcoma

  • Plasma cell myeloma (formerly multiple myeloma)

  • Metastatic cancer

  • Fibrous dysplasia

  • Osteitis fibrosa cystica

  • Fibrogenesis imperfecta ossium

  • Myelofibrosis

  • Intramedullary osteosclerosis

  • Erdheim-Chester disease

  • Langerhans cell histiocytosis

  • Sickle cell disease

Diagnosis

Laboratory Tests

  • Serum alkaline phosphatase markedly elevated

  • Other markers of bone turnover are also usually elevated, particularly

    • Serum procollagen type-I N-terminal propeptide (PINP)

    • Urine N-telopeptide of type 1I collagen cross-links (NTx)

  • Serum calcium may be elevated, particularly if patient is at bed rest

  • A serum 25-OH vitamin D should be obtained to screen for vitamin D deficiency, which

    • Can present with an increased serum alkaline phosphatase and bone pain

    • Should be corrected before prescribing a bisphosphonate

  • Sarcomatous change is suggested by sudden rise in serum alkaline phosphatase

Imaging Studies

  • Bone radiographs show involved bones as expanded and denser than normal

  • Multiple fissure fractures in long bones

  • Initial lesion may be destructive and radiolucent, ...

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