Paget's Disease

Question 1

Define Paget’s Disease of the bone

Answer 1

Chronic bone disorder characterised by focal areas of increase bone remodelling, resulting in overgrowth of poorly organised bone

Monostotic: involves only one bone (femur most common)

Polyostotic: involves more than one bone (usually femur, pelvis, skull or tibia)

Question 2

Aetiology of Paget’s Disease of the bone

Answer 2

Unknown
May be due to autosomal dominant disease, infection or environmental exposure to arsenic, cattle or dogs

1. An initial, short-lived burst of multinucleate osteoclastic activity causing bone resorption
2. A mixed phase of both osteoclastic and osteoblastic activity, with increased levels of bone turnover leading to deposition of structurally abnormal bone
3. A final chronic sclerotic phase, during which bone formation outweighs bone resorption.

Continued process of excessive, abnormal bone-forming activity + creation of microfractures -> deformities -> change in the biomechanical milieu of the adjacent joints. + old age = predisposition to arthritis.

Question 3

Symptoms of Paget’s Disease of the bone

Answer 3

Asymptomatic in most patients

Most commonly affects the femur and pelvis (75% of patients) and skull (37% of patients)

Long-bone or back pain (due to microfractures)
Pain - Pathological fractures (weakened pagetoid bone)
Bony deformities
Have to increase the size of their headwear
Progressive enlargement of the jaw
Increased local temperature (increased metabolic activity)
Hearing loss (CN VIII)
Facial pain (CN V)
Loosening teeth or disturbance in chewing
Deterioration of visual acuity (CN II)

Question 4

Signs of Paget’s Disease of the bone on examination

Answer 4

Spinal stenosis (due to narrowing of the spinal canal or by the blood-supply-steal mechanism)
Bony deformities: frontal bossing, prognathism, bone bowing
Deterioration of visual acuity (CN II involvement)

Question 5

Investigations for Paget’s Disease of the bone

Answer 5

Plain X-ray: abnormal pelvis, long bone and skull (early = lytic changes, advancing V-shaped lytic lesion in long bones, occasional fracture | later = sclerotic)

Bone scan: areas of dense uptake

Total serum alk phos: elevated or normal
Bone specific alk phos: elevated
Serum calcium: normal
Serum procollagen 1 N-terminal peptide (P1NP): initially elevated
Serum C-terminal propeptide of type 1 collagen (CTX): initially elevated
LFTs: normal
Serum 25-hydroxyvitamin D: normal

CT/MRI: pagetoid bone = capacipus and disorganised on cross-sectional studies

Bone biopsy: presence of osteoclasts with multiple nuclei/ Wide canaliculi with disorganised matrix in bone + mosaic pattern