Paget’s Disease (of the bone)

Increased osteoclast activity followed by increased but disorganised osteoblast activity, deforming bone. Male > female (approximately 1.4:1); 95% asymptomatic.

Clinical features

Usually asymptomatic. Some have deep aching bone pain, typically at night. May develop unequal leg length, or neuropathies if skull neural foramina are affected. Signs: bowing of the tibia, enlarged skull (hats stop fitting), waddling gait.

Investigations

• Raised serum alkaline phosphatase (often >1000), with normal calcium and phosphate. A normal GGT suggests the ALP is of bone origin; if there is concurrent liver/biliary disease, use bone-specific ALP.
• X-ray — dense, expanded bone, best seen in skull and pelvis.
• Bone scan — maps areas of active disease.

Management

Aim: relief of pain and prevention of neurological complications. Localised, asymptomatic disease needs no treatment.

Bisphosphonates — indicated for age <50, skull/vertebral lesions, active disease in weight-bearing bones or near major joints, neurological symptoms, hypercalcaemia, or planned orthopaedic surgery near an affected bone. IV zoledronic acid (single dose) is most effective; oral risedronate is an alternative if unavailable.

Beware the exceedingly rare osteogenic sarcoma (a progressive rise in ALP despite treatment).