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Paget Disease



General Considerations

  • Multifocal chronic skeletal disease due to chronic paramyxoviral infection
  • Prevalence
    • 3% of individuals >40 years
    • 10% of persons >80 years
    • Unusual <40 years
    • M:F = 2:1
  • Histology
    • Increased resorption and increased bone formation
    • Newly formed bone is abnormally soft with disorganized trabecular pattern
  • Active or Osteolytic phase
    • Aggressive bone resorption with lytic lesions
    • Replacement of hematopoietic bone marrow by fibrous connective tissue with numerous large vascular channels
  • Inactive or Quiescent phase
    • Decreased bone turnover with skeletal sclerosis and thickening of the cortex
  • Mixed pattern
    • Lytic and sclerotic phases frequently coexist

Clinical findings

  • Asymptomatic (1/5)
  • When symptomatic, symptoms may include
    • Fatigue
    • Enlarged hat size
    • Peripheral nerve compression
    • Neurologic disorders from compression of brainstem (basilar invagination)
    • Hearing loss, blindness
    • Facial palsy (narrowing of neural foramina) - rare
    • Pain from(a)primary disease process is rare so think of
      • Pathologic fracture
      • Malignant transformation
      • Secondary degenerative joint disease aggravated by skeletal deformity
    • High-output congestive heart failure from markedly increased perfusion (rare)
    • Increased alkaline phosphatase (increased bone formation)
    • Hydroxyproline increased (increased bone resorption)
    • Normal serum calcium + phosphorus

Sites of involvement

  • Usually polyostotic and asymmetric
    • Pelvis (75%) most common, followed by
      • Lumbar spine
      • Thoracic spine
      • Proximal femur
      • Calvarium
      • Scapula
      • Distal femur
      • Proximal tibia
      • Proximal humerus

Imaging Findings

  • Classical triad
    • Thickening of the cortex
    • Accentuation of the trabecular pattern
    • Increased size of bone
  • Cyst-like areas
  • Skull (involvement in 29-65%)
    • Inner and outer table involved
      • Leads to diploic widening
    • Osteoporosis circumscripta is well-defined lysis, most commonly in frontal bone producing well-defined geographic lytic lesion in skull
      • Represents early destructive phase of disease active stage)

      Paget skull

Osteoporosis circumscripta of frontal bone in lytic phase of Paget's disease

    • "Cotton wool" appearance represents mixed lytic and blastic pattern of thickened calvarium (later stage)
    • Basilar invagination with encroachment on foramen magnum
    • Deossification and sclerosis in maxilla
    • Sclerosis of skull base
  • Long bones (almost invariably starts at end of bone)
    • "Candle flame" or "blade of grass" pattern of lysis is the advancing tip of V-shaped lytic defect in diaphysis of long bone originating in subarticular site
    • Lateral curvature of femur
    • Anterior curvature of tibia (commonly resulting in fracture)
  • Pelvis
    • Thickened trabeculae in sacrum, ilium
    • Rarefaction in central portion of ilium (looks like a large lytic lesion)
    • Thickening of iliopectineal line
    • Acetabular protrusio with secondary degenerative joint disease
  • Spine (upper cervical, low dorsal, midlumbar most common sites)
    • Coarse trabeculations at periphery of bone
    • "Picture-frame vertebra" mimics bone-within-bone appearance
      • Enlarged vertebral body with reinforced peripheral trabeculae and more lucent center, typically in lumbar spine
    • "Ivory vertebra" is a blastic vertebra with increased density
    • Ossification of spinal ligaments, paravertebral soft tissue, disk spaces can occur

Bone scan

  • Sensitivity
    • Scintography and radiography (60%)
      • Scintography only (27%)
      • Radiography only (13%)
  • Usually markedly increased uptake (symptomatic lesions strikingly positive)
  • Normal scan may occur in some burned-out lesions
  • Marginal uptake can be seen in lytic lesions

Bone marrow scan

  • Sulfur colloid bone marrow uptake is decreased (marrow replacement by cellular fibrovascular tissue)

MRI Findings

  • Hypointense area / area of signal void on T1WI + T2WI (cortical thickening, coarse trabeculation)
  • Widening of bone
  • Reduction in size and signal intensity of medullary cavity due to replacement of high-signal-intensity fatty marrow by medullary bone formation
  • Focal areas of higher signal intensity than fatty marrow (from cyst-like fat-filled marrow spaces)
  • Areas of decreased signal intensity within marrow on T1WI and increased intensity on T2WI (= fibrovascular tissue resembling granulation tissue)

Complications

  • Associated neoplasia (0.7-20%)
  • Sarcomatous transformation into osteosarcoma (22-90%), fibrosarcoma /malignant fibrous histiocytoma (29-51%), chondrosarcoma (1-15%)
  • Sarcomas are usually osteolytic in pelvis, femur, humerus
  • Giant cell tumor occurs in 3-10%
    • Lytic expansile lesion in skull, facial bones
  • Lymphoma or plasma cell myeloma are reported
  • Fracture
    • "Banana fracture" = tiny horizontal cortical infractions (“Looser lines”)on convex surfaces of lower extremity long bones (lateral bowing of femur, anterior bowing of tibia)
    • Compression fractures of vertebrae
  • Early-onset osteoarthritis

Treatment

  • Calcitonin, diphosphonate, mithramycin
  • Detection of recurrence:
    • In 1/3 detected by bone scan
    • In 1/3 detected by biomarkers (alkaline phosphatase, urine hydroxyproline)
    • In 1/3 by scan and biomarkers simultaneously

DDx

  • Depends on the bone in which it occurs
  • Skull
    • Osteolytic or osteoblastic metastases
  • Long bones
    • Metastases
    • Chronic osteomyelitis (thickened cortex)
    • Old trauma (thickened cortex)
    • Hodgkin’s disease
  • Spine
    • Hemangioma
    • Metastases

Paget's Disease -- pelvis. Frontal radiograph of the pelvis demonstrates the classical triad of thickening of the cortex (blue arrow), accentuation of the trabecular pattern (red circle) and increased density of the bone.
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Paget Disease, Left Hemipelvis. The entire left hemipelvis demonstrates increased bone density with thickening of the cortex and accentuation of the trabecular markings characteristic of paget Disease.