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# Paget disease of bone

A bone disease in which old bone is broken down and rebuilt too fast and in disorder, making bones large, weak and painful. Often found by chance.

Updated 2026-11-01

## Structures involved

Tap one to see what it is and open it in 3D.

- [Hip bone](https://durgical.com/en/anatomy/hip-bone/)
- [Frontal bone](https://durgical.com/en/anatomy/frontal-bone/)
- [Femur](https://durgical.com/en/anatomy/femur/)
- [Tibia](https://durgical.com/en/anatomy/tibia/)
- [Parietal bones](https://durgical.com/en/anatomy/parietal-bone/)
- [Vestibulocochlear nerve (VIII)](https://durgical.com/en/anatomy/vestibulocochlear-nerve/)
- [Cochlea](https://durgical.com/en/anatomy/cochlea/)

## Why it happens

- [Bone remodeling](https://durgical.com/en/physiology/bone-remodeling/)
- [Alkaline phosphatase (ALP) as a lab test](https://durgical.com/en/biochemistry/topics/alkaline-phosphatase-as-a-lab-test/)
- [Bone tissue: cells, compact and spongy bone](https://durgical.com/en/histology/bone-tissue-cells-compact-and-spongy-bone/)

## What it is

A localised disorder of bone remodelling in which overactive osteoclasts are followed by disorganised new bone formation. The affected bones become enlarged, deformed and mechanically weak. It most often affects the [pelvis](https://durgical.com/en/anatomy/region/pelvis/), [spine](https://durgical.com/en/anatomy/region/spine/), skull, [femur](https://durgical.com/en/anatomy/femur/) and [tibia](https://durgical.com/en/anatomy/tibia/).

## Who gets it

Mainly a disease of people over 50 and more common in those of British and Northern European ancestry; it appears less common in Latin America, but cases occur and many are found incidentally. Its frequency has fallen in recent decades.

## Causes

- Genetic predisposition: mutations in SQSTM1 in many familial cases
- A possible environmental trigger, such as an earlier viral infection, has been proposed but not proven
- Cause unknown in most people

## Risk factors

- Age over 50
- Family history of Paget disease
- Northern European ancestry

## Pathophysiology

Large, overactive osteoclasts resorb bone; osteoblasts respond by laying down new bone quickly and chaotically, giving a mosaic pattern of woven bone. In the late stage, bone is thick and sclerotic but weak. Increased vascularity can raise cardiac output, and expanded bone can compress nerves.

## Classification

- Monostotic: one bone affected
- Polyostotic: several bones affected
- Phases: lytic, mixed and sclerotic

## Symptoms and signs

- Often asymptomatic; found by a raised alkaline phosphatase or on an X-ray
- Deep, aching bone pain, often worse at night
- Bowing of the femur or tibia and warmth over the affected bone
- Enlarging skull with headache and an increasing hat size
- Hearing loss from skull involvement
- Secondary osteoarthritis of the hip or knee

## Red flags

- New or rapidly worsening pain with swelling at a pagetic site (sarcomatous change)
- Pathological fracture
- Leg weakness, bladder or bowel changes ([spinal cord](https://durgical.com/en/anatomy/spinal-cord/) compression)
- High-output heart failure in extensive disease

## Diagnosis

**Clinical**
Bone pain or deformity in an older adult, or an incidental finding. Examination of long bones, skull and hearing.

**Tests**
Raised serum total or bone-specific alkaline phosphatase with normal calcium and phosphate; alkaline phosphatase is also used to monitor activity. [Liver](https://durgical.com/en/anatomy/liver/) tests to exclude a hepatic source.

**Imaging**
Plain X-rays show thickened cortices, coarse trabeculae, bone enlargement and lytic areas (osteoporosis circumscripta in the skull). A radionuclide bone scan maps the extent of disease.

## Differential diagnosis

- Osteoblastic bone metastases (e.g. [prostate](https://durgical.com/en/anatomy/prostate/) cancer)
- Primary hyperparathyroidism
- Osteomalacia
- Fibrous dysplasia
- Osteosarcoma

## Goal of treatment

Relieve bone pain, suppress abnormal bone turnover and prevent or manage complications such as deformity, fracture and osteoarthritis.

## Treatment

**Medical**
Bisphosphonates (zoledronic acid as a single infusion is highly effective) are first-line; vitamin D and calcium status is corrected first to avoid hypocalcaemia. Calcitonin is a second-line option.

**Medical**
Analgesics and non-steroidal anti-inflammatory drugs for pain and associated osteoarthritis.

**Surgical**
Fixation of fractures, osteotomy for severe bowing and joint replacement for advanced arthritis; bisphosphonates beforehand reduce bleeding from vascular bone.

**Follow-up**
Alkaline phosphatase periodically to detect relapse; hearing assessment when the skull is involved.

## Complications

- Pathological fractures
- Secondary osteoarthritis
- Conductive or sensorineural hearing loss
- Spinal stenosis and nerve compression
- High-output heart failure
- Osteosarcoma (rare)

## Prognosis

Usually good: treatment controls pain and bone turnover in most patients. The outlook is poor in the rare cases complicated by osteosarcoma.

## Test yourself

Think of the answer, then tap the question to see it.

## What is the typical laboratory finding in Paget disease of bone?

Isolated raised alkaline phosphatase with normal calcium and phosphate.

## Which cell is primarily abnormal in Paget disease?

The osteoclast, which is enlarged and overactive, followed by disorganised osteoblastic bone formation.

## What is the first-line drug class for symptomatic Paget disease?

Bisphosphonates, such as zoledronic acid.

## Which rare malignant complication should be suspected with new pain and swelling in pagetic bone?

Osteosarcoma.

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## Related conditions

- [Osteosarcoma](https://durgical.com/en/conditions/osteosarcoma/)
- [Hearing loss (conductive and sensorineural, including sudden hearing loss)](https://durgical.com/en/conditions/hearing-loss/)
- [Hip Osteoarthritis](https://durgical.com/en/conditions/hip-osteoarthritis/)
- [Knee Osteoarthritis](https://durgical.com/en/conditions/knee-osteoarthritis/)
- [Heart failure](https://durgical.com/en/conditions/heart-failure/)
- [Lumbar spinal stenosis](https://durgical.com/en/conditions/lumbar-spinal-stenosis/)
- [Osteoporosis](https://durgical.com/en/conditions/osteoporosis/)
- [Primary hyperparathyroidism](https://durgical.com/en/conditions/primary-hyperparathyroidism/)

Educational information, not medical advice. For any symptom, see a health professional.

Sources: [Paget disease of the bone](https://medlineplus.gov/ency/article/000414.htm) (MedlinePlus Medical Encyclopedia (U.S. National Library of Medicine), 2025).

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Source: https://durgical.com/en/conditions/paget-disease-of-bone/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/conditions/paget-disease-of-bone/