My Clinical Notes

• Can be divided into stages;
  • An initial osteolytic stage
  • Followed by a mixed osteoclastic-osteoblastic stage which ends in a predominance of osteroblastic activity
  • Eventually evolves into a burnt out osteosclerotic stage

 

• Usually begins in middle age and gets more common with increasing age
• Geographical and racial variation

 

Pathogenesis

 

• Current evidence suggests it is caused by a slow virus infection such as paramyxovirus
• Possible that virally infected cells produce IL-6 and M-CSF which are potent recruiters and stimulators of osteoclasts
• Other evidence suggests that osteoclasts may be hyperresponsive to RANKL signalling and vitamin D
• Occasionally it is associated with an inherited component with predisposition linked to a locus on chromosome 18

 

Morphology

 

• It is a focal disease with much variation in the stage of disease at different sites

• Histological hallmark is the mosaic pattern of lamellar bone
• In the initial lytic phase there are waves of osteoclastic activity and numerous reabsorption pits
• Osteoclasts are abnormally large containing more than the normal number of 10-12 nuclei
• The newly formed bone may be woven or lamellar but eventually all is remodelled into lamellar bone
• As the cell activity decreases the fibrovascular tissue that developed in the marrow adjacent to the bone forming surface recedes and is replaced with normal marrow.
• In the end the bone is thickened an composed of course thickened trabeculae and the cortices are soft and porous and lack structural stability

 

Clinical course

 

• Most cases are mild and are discovered incidentally radiologically
• Disease can produce a variety of skeletal, neuromuscular and cardiovcascular complications
• Diagnosis made radiologically and via measurement of high levels of alkaline phosphatase and increased urine secretion of hydroxyproline
• Affects one bone in 15% of cases – tibia, ilium, femur, skull, vertebrae, humerus
• Polystotic disease affects the pelvis, spine and skull
• Pain in the most common feature and is localised to the affected bone
• Pain is caused by microfractures and bone overgrowth that compresses on the spinal and cranial nerve roots
• The overgrowth of the craniofacial skeleton may make the head too heavy for the patient to hold up
• Weakness of the base of the skull may lead to compression of the posterior fossa structures
• Weight bearing can distort the femoral heads and cause secondary osteoarthritis
• Chalkstick type fractures occur in the long bones of the lower linb
• Compression fractures can occur in the spine
• The hypervascularity of Paget bone warms the overlying skin. In severe polyostotis disease the increased blood flow behaves as a arteriovenous shunt leading to high output cardiac failure and exacerbation of underlying disease
• A variety of tumours can develop in Paget bone;
• Benign tumours include giant cell tumour, giant cell reparative granuloma and extraosseous masses of haematopoesis.
• Malignancy – sarcomas, osteosarcomas, malignant fibrous histiocytoma, chondrosarcoma. Arise in the long bones, skull, pelvis and spin

 

• Most patients have mild disease however and are managed with calcitonin and bisphosphonates

This entry was posted on Thursday, November 15th, 2007 at 2:13 pm and is filed under Orthopaedics. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.