Paget’s disease - Metabolic bone disorders

Paget’s disease

Definition

A disorder of bone remodelling with accelerated rate of bone turnover.

Prevalence

Common with 10% of adults affected by age 90.

Age

Rare before 40 years.

Sex

M = F

Aetiology

There may be a genetic component as there is a familial tendency. There are families with an autosomal dominant inheritance of Paget’s disease. Viral infections may also be involved in the aetiology, including canine distemper virus and measles. Paget’s disease may be due to a latent infection in a genetically susceptible individual.

Pathophysiology

Osteoclastic overactivity causes excessive bone resorption. There follows osteoblast activation in an attempt to repair the lesion. The resultant bone is larger than normal, but abnormal architecture predisposes to fractures.

Clinical features

Most patients are asymptomatic and the disease is discovered incidentally on routine X-ray. Patients may complain of a dull pain, which is worse at night. On examination the bone may be bent and thickened, most obvious if the tibia is affected (sabre tibia). With widespread bone involvement there may be a bowing of the legs and considerable kyphosis.

Complications

Nerve compression may cause pain. Skull involvement may lead to compression of the VIIIth nerve resulting in deafness. High output cardiac failure may occur due to shunting of blood through the vascular bone. Fractures are common especially in the weight-bearing long bones. Osteogenic sarcoma may occur due to Paget’s disease and carries a poor prognosis. It may cause a marked increase in bone pain.

Investigations

Characteristically there is a very high serum alkaline phosphatase with a normal serum calcium and phos-phate reflecting the high bone turnover. However, during periods of immobilisation in active disease the serum calcium level may rise dramatically. Imaging shows enlargement of bone, osteolysis and sclerosis.

Management

Asymptomatic Paget’s disease requires no treatment, patients with persistent bone pain, repeated fractures, neurological complications or high cardiac output are treated with calcitonin and/or bisphosphonates, which suppress bone turnover. Surgical intervention may be required.