FFinalistSouthampton · 2027
Endocrine
AKT · Endocrine/Calcium, bone & parathyroidlow yield

Paget's disease of bone

Disordered osteoclast-driven bone remodelling

Overview

Localised disordered bone turnover — excessive osteoclastic resorption followed by disorganised osteoblastic formation, producing enlarged, structurally weak, deformed bone. Often asymptomatic with an isolated raised ALP; can cause bone pain, deformity (bowed tibia, skull enlargement), fractures, deafness, and (rarely) osteosarcoma. Calcium is normal. Treated with a bisphosphonate if symptomatic.

Recognise

  • Often asymptomatic — incidental ISOLATED raised alkaline phosphatase with normal calcium/phosphate
  • Bone pain, deformity (bowing of long bones, enlarging skull/hat size), warmth over affected bone; pathological fracture
  • Complications: deafness (skull/ossicles), high-output cardiac failure (extensive disease), spinal stenosis, rare osteosarcoma

Red flags

  • New severe pain/soft-tissue mass in Pagetic bone → exclude osteosarcoma
  • Pathological fracture; neurological compression (skull base/spine)

Differentials & how to tell them apart

Osteomalaciahigh ALP but with LOW calcium/phosphate/vitamin D and proximal myopathy
Bone metastases / myelomaraised ALP/calcium, lytic lesions, known/occult cancer
Hyperparathyroidismhigh calcium with raised PTH
Liver diseaseraised ALP of hepatic origin — GGT also raised

Investigations

Isolated raised ALP with NORMAL calcium/phosphate; X-ray (lytic + sclerotic, cortical thickening, bowing); isotope bone scan (extent). Exclude other causes of raised ALP (liver — check GGT).

Management

Bisphosphonate (for bone pain/active symptomatic disease)

  1. 1Confirm isolated raised ALP with normal calcium (check GGT to exclude liver source) and X-ray changes. Treat SYMPTOMATIC disease (bone pain) with a bisphosphonate; analgesia.Gate: A new lytic area or soft-tissue mass with rapidly worsening pain in Pagetic bone raises OSTEOSARCOMA — investigate, don't just escalate analgesia
  2. 2Manage complications: hearing aids/ENT (deafness), orthopaedics (fracture/deformity/arthroplasty), spinal decompression; monitor ALP response.
Bisphosphonate (oral risedronate / IV zoledronate) — first-line for symptomatic disease — suppresses bone turnover, relieves pain
Analgesia — for bone pain

Key points

Isolated raised ALP + normal calcium + bone deformity/deafness in an older patient = Paget's. Bisphosphonate for pain. The rare but feared complication is osteosarcoma.

Monitor & prognosis

ALP (response/relapse); complications.

Good; rare malignant transformation.

Source: Society for Endocrinology; Paget's Association