Paget's Disease of Bone

Paget's disease of bone, also known as osteitis deformans, is a chronic condition that affects bone remodelling, leading to deformity and potential complications. The disease is characterised by dysregulated bone remodelling, with excessive bone resorption followed by disorganised new bone formation. This process results in structurally weak and deformed bones, potentially causing pain, fractures, and arthritis.

Signs and Symptoms

Early stages of Paget's disease are often asymptomatic and may be discovered incidentally during investigations for other conditions. When symptomatic, the most common presentation is bone pain. Symptoms can be mistaken for arthritis or other disorders, delaying diagnosis. Involvement of the skull can lead to frontal bossing, increased hat size, headaches, hearing loss due to auditory foramen narrowing, and rarely, vision loss due to nerve compression.

Paget's disease is also associated with various conditions like osteoarthritis, heart failure, kidney stones, nervous system problems, dental issues, and angioid streaks. Unlike osteoporosis, Paget's disease does not affect the entire skeleton and does not spread from bone to bone.

Causes

Paget's disease may have both viral and genetic origins. Viral theories suggest a slow infection by paramyxoviridae, but recent evidence questions the involvement of measles virus due to possible laboratory contamination. Genetically, mutations in SQSTM1 and RANK genes, along with specific regions on chromosomes 5 and 6, have been implicated. About 40–50% of hereditary cases and 10–15% of sporadic cases involve mutations in the SQSTM1 gene.

Pathogenesis

Paget's disease progresses through four stages: osteoclastic activity, mixed osteoclastic-osteoblastic activity, osteoblastic activity, and malignant degeneration. Initially, increased osteoclastic activity leads to bone resorption, followed by compensatory osteoblastic activity creating disorganised bone. This results in a chaotic trabecular bone pattern, known as the "mosaic" pattern. The disease may eventually progress to dense "pagetic bone," characterised by hypervascular fibrous tissue replacing normal bone marrow.

Diagnosis

Diagnosis includes elevated alkaline phosphatase levels in the blood, characteristic X-ray findings, and bone scans. Additional tests like urinary markers of bone turnover and serum hydroxyproline levels support the diagnosis.

Treatment

Treatment aims to relieve pain and prevent disease progression. Bisphosphonates are the primary medications, including risedronic acid, alendronic acid, pamidronic acid, and zoledronic acid. Calcitonin is less commonly used due to potential cancer risks and limited efficacy.

Surgery

Surgical intervention may be necessary for fractures, severe arthritis, and bone deformities. Procedures like joint replacement or osteotomy can improve functionality and reduce pain.

Diet and Exercise

Patients should ensure adequate intake of calcium and vitamin D, especially when on bisphosphonates. Exercise is essential for maintaining skeletal health and joint mobility, but should be discussed with healthcare providers to avoid stress on affected bones.

Prognosis

Paget's disease is progressive but often minimally symptomatic. Treatment focuses on symptom management as there is no cure. Osteogenic sarcoma is a rare but serious complication, occurring in less than 1% of cases.

Epidemiology

Paget's disease is the second most common metabolic bone disorder after osteoporosis. It primarily affects older adults, with a higher prevalence in men and individuals of European descent. Familial cases are inherited in an autosomal dominant pattern, although incomplete penetrance is common.

History

First described by Sir James Paget in 1877, the disease was initially termed osteitis deformans. Paget's observations of mixed bone destruction and regeneration align with modern understanding of the disease.

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Self-assessment MCQs (single best answer)

What is Paget's disease of bone also known as?

Which symptom is most commonly associated with symptomatic Paget's disease?

Which gene mutation is most frequently implicated in hereditary cases of Paget's disease?

What is the characteristic histological pattern seen in Paget's disease of the bone?

Which of the following is NOT a common complication associated with Paget's disease?

Which diagnostic test is most indicative of Paget's disease?

What is the primary medication class used to treat Paget's disease?

Which surgical procedure might be required for patients with severe Paget's disease complications?

What dietary components are important for patients with Paget's disease to ensure adequate intake?

Paget's disease was first described by which scientist?