Paget's Disease of Bone
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Paget's Disease of Bone (Osteitis Deformans) is a chronic disorder of bone remodelling. It involves excessive Resorption (by Osteoclasts) followed by chaotic Formation (by Osteoblasts), leading to disorganized, weak "woven" bone that is prone to deformity and fracture.
Clinical Scenario: The Tight Hat
A 70-year-old man presents with a dull ache in his right hip and deafness in his left ear. He mentions his hat size has increased over the last 5 years. Blood tests show an isolated Alkaline Phosphatase (ALP) of 900 IU/L (Normal <130).
Key Teaching Points
- **Diagnosis**: **Paget's Disease**.
- **Skull Enlargement**: Causes the hat sign and nerve compression (Deafness).
- **Biochem**: **Isolated Raised ALP** is the hallmark. Calcium and Phosphate are usually normal (unlike Osteomalacia).
- **Action**: Isotope Bone Scan to define extent.
Image Integration Plan
| Image Type | Source | Status |
|---|---|---|
| Management Algorithm | AI-generated | PENDING |
| Skull X-Ray (Cotton Wool) | Web Source | PENDING |
| Tibial X-Ray (Sabre Shin) | Web Source | PENDING |
| Histology (Mosaic Pattern) | Web Source | PENDING |
[!NOTE] Image Generation Status: Diagrams illustrating the Osteoclast-Osteoblast uncoupling are queued.
Phases of Disease
- Lytic Phase: Osteoclasts go wild. Resorption.
- Mixed Phase: Osteoblasts try to compensate. Chaotic bone formation.
- Sclerotic Phase: Osteoblasts dominate. Bone is hard, dense, but weak. (Burned out).
- Prevalence: Common in UK/Europe (up to 5% of men >55 years). Rare in Asia/Africa.
- Age: >55 years.
- Sex: Male > Female (3:2).
- Genetics: SQSTM1 mutation in familial cases.
- Osteoclast Defect: Giant multi-nucleated osteoclasts resorb bone rapidly.
- Chaotic Repair: Osteoblasts lay down non-lamellar "woven" bone.
- Vascularity: The marrow becomes highly vascular (can feel warm on palpation).
- Result: Bones are expanded but structurally weak.
Majority (70%) are Asymptomatic (Incidental high ALP).
- Look: Deformity (Bowing)? Skull size?
- Feel: Increased warmth over the affected bone (vascularity).
- Move: Restricted ROM (secondary osteoarthritis).
- Biochemistry:
- ALP: Markedly Elevated. Reflects extent of disease.
- Calcium/Phosphate: Normal (Essential for exclusion of other metabolic bone disease).
- Urine Hydroxyproline: High (marker of collagen breakdown).
- X-Ray:
- Skull: "Osteoporosis Circumscripta" (Lytic) -> "Cotton Wool Spots" (Sclerotic).
- Long Bones: Thickened cortex, coarse trabeculation, bowing.
- Vertebrae: "Picture Frame" Vertebrae.
- Isotope Bone Scan: Most sensitive. Shows "Hot Spots" of activity.
A. Indications for Treatment
Not everyone needs treatment. Treat if:
- Bone Pain.
- Neurological Complications (Deafness/Radiculopathy).
- Deformity.
- High Output Failure.
- Preparation for Surgery (e.g. Hip Replacement) - to reduce bleeding.
B. Pharmacotherapy
Goal: Suppress Osteoclasts.
- Bisphosphonates (Mainstay):
- Zoledronic Acid: 5mg IV infusion (Single dose). Highly effective. Remission can last years. First line.
- Risedronate: Oral (30mg daily for 2 months).
- Calcitonin: Rarely used now (less effective).
C. Analgesia
- NSAIDs / Paracetamol.
D. Surgical
- Joint Replacement (for secondary OA).
- Osteotomy (for severe deformity).
- Osteosarcoma (<1%):
- Suspect if sudden increase in pain or new swelling.
- Very poor prognosis.
- Fractures: Chalk-stick fractures.
- Hypercalcaemia: Only occurs if patient is immobilized.
- Chronic progressive disease.
- Treatment controls symptoms but does not reverse deformity.
- Normal life expectancy (unless Osteosarcoma develops).
- Paget's Association Guidelines (UK).
- PRISM Trial: Intensive vs Symptomatic management (showed intensive Rx didn't reduce fracture risk, but improved pain).
What is Paget's Disease? Your bones are constantly being recycled – old bone is taken away and new bone is laid down. In Paget's, this process goes into overdrive. The "demolition crew" (osteoclasts) works too fast, and the "builders" (osteoblasts) panic and slap down new bone in a messy, chaotic way. The result is bone that is bigger and thicker than normal, but actually weaker and jumbled up.
Is it cancer? No. It is a benign metabolic condition. However, in very rare cases (less than 1 in 100), the active bone cells can turn into a bone cancer called osteosarcoma.
Why is my head getting bigger? The skull is a common place for this "overgrowth" to happen. As the bone thickens, it can make your hat feel tight and can sometimes squeeze the nerve to your ear, causing deafness.
How do we treat it? We use a drip called Zoledronic Acid. It acts like a brake on the "demolition crew", slowing the bone turnover back to normal speeds. One dose can work for years.
- Ralston SH, et al. Diagnosis and management of Paget's disease of bone in adults: A clinical guideline. J Bone Miner Res. 2019.
- Tan A, et al. Long-term randomized trial of intensive versus symptomatic management in Paget's disease of bone: The PRISM-EZ study. J Bone Miner Res. 2017.
- Reid IR, et al. Comparison of a single infusion of zoledronic acid with risedronate for Paget's disease. N Engl J Med. 2005.