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Osteoporosis Circumscripta

Paget’s Disease

 

  • 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

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
      • Scintigraphy and radiography (60%)
        • Scintigraphy 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)
  • MR
    • 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

 

Dahnert 4th Edition

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