Paget Disease of Bone

OBJECTIVES

The learner will be better able to:
1) Explain the principles reflected in the history and discovery of Paget Disease of Bone
2) Generate a differential diagnosis given a patient case
3) Describe the distinct features of a radiological image of a patient with Paget Disease of Bone
4) Explain factors that influence the incidence of Paget Disease of Bone in a given population
5) Identify classic features of Paget Disease of Bone given a patient case

INTRODUCTION

Paget Disease of Bone, or osteitis deformans, is a condition of older individuals characterized by progressive skeletal deformation due to problems in bone resorption and remodeling. Likely due to a viral infection, it stimulates an increase in osteoclast activity. This leads to increased bone resorption coupled with abnormal and excessive bone remodeling.

EPIDEMIOLOGY

In the United States it occurs in approximately 3% to 5% of the population over 50 years of age. In some studies, the incidence approaches 10% of the population over 80 years of age. The disease is rarely reported among patients under 40, likely because of the asymptomatic nature of its initial presentation. The disease is commonly diagnosed as an incidental finding on X-rays for chronic bone pain or arthritis. The particular geographic distribution of the disease suggests that genetic and environmental factors play a role in its development. Paget Disease is fairly common in the United States, England, Australia, New Zealand, France and Germany. In addition, countries with heavy immigration from Western Europe have higher incidence than countries without. On the other hand, Paget Disease is uncommon in African, Asian and Middle Eastern countries.

ETIOLOGY

Recent studies suggest Paget Disease is due to a viral infection. A metabolic disorder or mechanism does not seem likely because of the way that the disease manifests itself. It is not uncommon for skeletal deformities to develop in certain bones, while proximal structures remain unaffected. In the cases in this series the tibia is affected but the fibula was completely spared. The growth of one bone while it remained tethered to another bone, such as the tibia in its relationship to the fibula, gives the characteristic bowing of the limb, a secondary response to the biomechanic constraints of the skeleton.

CLINICAL DIAGNOSIS AND MANIFESTATIONS

Paget Disease is often asymptomatic and may take months to years to diagnose. Skeletal bone deformity and enlargement may be the first presentation. Disease which is clinically evident usually affects the entire bone, typically the long bones and skull. When pathologic fractures develop, malunion or nonunion often ensue due to the abnormal bone remodeling.

As the name suggests, Paget Disease of Bone affects the musculoskeletal system. Most patients will complain of arthritis, bone tenderness or joint pain as the bones become increasingly deformed. Back pain is very common when vertebral bodies are affected and can be debilitating in older patients. In more severe cases, bone fractures and spinal column deformities can develop.

Non-skeletal manifestations of Paget Disease are secondary findings, typically from advanced disease. However, these outcomes can be traced back to skeletal abnormalities. Vertebral body enlargement can lead to spinal cord or peripheral nerve compression. When the skull is allowed to deform and become enlarged, it can lead to increased intra-cranial pressure, hydrocephalus or even cranial nerve deficits such as loss of hearing. Increased cardiac output results from increased bone vascularity, a cause of cardiovascular disease in some patients. Osteosarcomas, chondrosarcomas, malignant fibrous histiocytoma and giant cell tumors have been observed in patients with Paget Disease.

DIFFERENTIAL DIAGNOSIS

Paget Disease of bone is fairly common, though there is evidence that it is becoming less so. It is a condition of late middle age and old age. If the patient is under 40 years of age you are almost certainly dealing with something else.

Some instances of osteomalacia resemble Paget disease. However the entire skeleton is involved which excludes Paget Disease. Occasionally the skeletal system may be involved with Paget Disease and some other disease and it may be impossible to tell the two conditions apart. Most notable confusion is in a patient with Paget Disease who also has blastic metastases from carcinoma of the prostate. Combined involvement with metastases from other primaries and with some infections may present much difficulty in diagnosis. History, laboratory work, and review of prior examinations and viewing of roentgenograms of other parts of the skeletal system help in solving the problem.

SUMMARY

Paget Disease of Bone is characterized by increased bone growth and irregular bone remodeling. It is more common in elderly patients and rarely diagnosed before the age of 40. The disease is fairly asymptomatic and can take years to diagnose. Oftentimes, it is incidentally diagnosed on patients receiving X-rays for back pain or arthritis. Complications include skeletal deformity, bone fractures and nerve compression. Bone tenderness and joint pain can be accompanied by decreased mobility, affecting the daily function and quality of life of patients. Surgical and rehabilitative procedures are available in managing such complications.

REFERENCES

1. Kaplan FS, Singer FR: Paget's disease, in Morley JE, Korenman SG (eds): Endocrinology and Metabolism in the Elderly. Boston: Blackwell Scientific Publications, 1992, pp 230-240.

2. Ankron MA, Shapiro JR: Paget's Disease of Bone (Osteitis Deformans): Journal of the American Geriatrics Society 1998;46:1025-1026.

3. Barker DJP: The epidemiology of Paget's disease of bone: Brittish Medical Bulletin 1984;40:396-400.

4. Kaplan FS: Surgical management of Paget's disease: Journal of Bone and Mineral Research 1999;14:34-38