Makindo Medical Notes

Related Subjects: | Bisphosphonates | Osteoporosis

Paget’s disease of bone is a chronic disorder of bone remodelling, with focal areas of increased osteoclastic resorption followed by disorganized osteoblastic repair. The result is structurally weak, enlarged, and deformed bone. It is the second most common metabolic bone disease after osteoporosis.

About 🔎

• Disorder of bone remodelling → excessive osteoclastic activity followed by compensatory, poorly organized bone formation.
• Incidence increases with age: rare <50 years, but affects ~5% of people >55 years in the UK.
• Strong geographic clustering: more common in the UK, Western Europe, and North America.
• Often discovered incidentally on blood tests (raised ALP) or X-rays for another reason.

Aetiology 🧬

• Exact cause uncertain; evidence for both genetic and environmental triggers.
• Mutations in SQSTM1 gene in some familial cases.
• Possible viral link (paramyxovirus particles found in osteoclasts in some studies).
• Increased osteoclast number and size with inclusion bodies is a hallmark finding.

Clinical Features 🦴

• Often asymptomatic, detected incidentally on raised ALP.
• Bone pain – dull, constant, often worse at night, not relieved by rest.
• Bone deformity: bowed tibia (“sabre tibia”), skull enlargement → increasing hat size, kyphosis.
• Neurological: Deafness (conductive + SNHL), cranial nerve palsies, spinal stenosis.
• Complications: Pathological fractures, secondary osteoarthritis, high-output cardiac failure (rare).
• Malignant transformation: Osteosarcoma or fibrosarcoma (~1% of patients, poor prognosis).

Investigations 🧪

• Bloods: Isolated raised ALP (normal Ca, phosphate, LFTs).
• Urinary markers: Hydroxyproline ↑ (bone resorption marker).
• X-ray: Mixed lytic and sclerotic lesions, cortical thickening, bone enlargement, “cotton wool skull.”
• Bone scan (Tc-99m): Highly sensitive – shows disease extent, though not specific.

Management 💊

Exam Tips 🎓

• Think of Paget’s when you see isolated high ALP in an older adult with normal calcium.
• “Cotton wool skull” on X-ray is a classic buzzword.
• Bone pain + deformity + deafness = Paget’s triad.
• Differentiate from osteoporosis (normal ALP, diffuse bone thinning) and osteomalacia (low Vit D, low Ca/phosphate, raised ALP).

References 📚

• UK Paget’s Association Clinical Guidelines
• BMJ Best Practice: Paget’s Disease