Paget disease of bone. Diagnosis and indications for treatment

BACKGROUND

Paget disease was first described in 1877 by Sir James Paget. It is a focal disorder of bone remodelling, involving increased bone resorption and formation. The aetiology is uncertain but both environmental and genetic factors are thought to be involved in pathogenesis.

OBJECTIVE

This article outlines the clinical presentation, diagnosis and treatment of Paget disease.

DISCUSSION

Paget disease is associated with musculoskeletal pain, significant disability and impaired quality of life. Complications include pathological fracture, arthritis in adjacent joints, hearing loss, other neurological complications, heart failure and, rarely, osteosarcoma. Recent clinical trial data has demonstrated histological and radiological improvements in bone of patients treated with bisphosphonates. There is little data evaluating the long term effect of therapy on the risk of complications, however, restoration of normal bony architecture offers the prospect that complications related to deformity and increased bone fragility might be reduced by effective therapy.

Paget's disease of bone

Paget's disease of bone is characterized by an anarchic bone remodelling, associated with morphological and functional abnormalities of osteoclasts. Its prevalence and incidence rates decreased gradually over the past two decades; the reason for this remains unclear. The aetiology of the disease is still obscure, the paramyxoviral theory being very controversial. Recent advances in understanding of the disease come from genetic studies, with the identification of specific mutations in the p62-sequestosome gene, which could be involved in pathogenetic mechanisms leading to increased osteoclast activity. The disease affects one or several bone pieces, leading to bone pain, deformities, characteristic imaging features, and increased markers of bone remodelling. The long-lasting disease activity leads to complications, including arthropathies, neurological compressions, fissures or fractures and, rarely, osteosarcomatous transformation of a pagetic lesion. Potent bisphosphonates have proven their efficacy in reducing symptoms and disease activity. They are currently used as the first-line treatment with the goal of normalizing bone remodelling and, hopefully, preventing late complications.

Principles of management of osteometabolic disorders affecting the aging spine

Osteoporosis is the most common contributing factor of spinal fractures, which characteristically are not generally known to produce spinal cord compression symptoms. Recently, an increasing number of medical reports have implicated osteoporotic fractures as a cause of serious neurological deficit and painful disabling spinal deformities. This has been corroborated by the present authors as well. These complications are only amenable to surgical management, requiring instrumentation. Instrumenting an osteoporotic spine, although a challenging task, can be accomplished if certain guidelines for surgical techniques are respected. Neurological deficits respond equally well to an anterior or posterior decompression, provided this is coupled with multisegmental fixation of the construct. With the steady increase in the elderly population, it is anticipated that the spine surgeon will face serious complications of osteoporotic spines more frequently. With regard to surgery, however, excellent correction of deformities can be achieved, by combining anterior and posterior approaches. Paget's disease of bone (PD) is a non-hormonal osteometabolic disorder and the spine is the second most commonly affected site. About one-third of patients with spinal involvement exhibit symptoms of clinical stenosis. In only 12-24% of patients with PD of the spine is back pain attributed solely to PD, while in the majority of patients, back pain is either arthritic in nature or a combination of a pagetic process and coexisting arthritis. In this context, one must be certain before attributing low back pain to PD exclusively, and antipagetic medical treatment alone may be ineffective. Neural element dysfunction may be attributed to compressive myelopathy by pagetic bone overgrowth, pagetic intraspinal soft tissue overgrowth, ossification of epidural fat, platybasia, spontaneous bleeding, sarcomatous degeneration and vertebral fracture or subluxation. Neural dysfunction can also result from spinal ischemia when blood is diverted by the so-called "arterial steal syndrome". Because the effectiveness of pharmacologic treatment for pagetic spinal stenosis has been clearly demonstrated, surgical decompression should only be instituted after failure of antipagetic medical treatment. Surgery is indicated as a primary treatment when neural compression is secondary to pathologic fractures, dislocations, spontaneous epidural hematoma, syringomyelia, platybasia, or sarcomatous transformation. Five classes of drugs are available for the treatment of PD. Bisphosphonates are the most popular antipagetic drug and several forms have been investigated.

Paget's disease and fibrous dysplasia

Paget's disease and fibrous dysplasia are benign disorders that can involve the temporal bone and skull base. They commonly lead to otolaryngologic symptoms such as impingement of cranial nerves or the orbit or blockage of the external auditory canal or paranasal sinuses, although they can often be a challenge to diagnose because of their insidious presentation. Their benign nature and common presentation within the difficult-to-access confines of the skull base should lead the clinician to exercise caution in their treatment, reserving surgical intervention for either diagnosis or the relief of symptoms. As a better understanding of the etiology of these conditions develops and new pharmacotherapeutic agents are tested, it is likely that physicians will be able to turn to medical rather than surgical techniques to treat these disorders.

The current status of Paget's disease of the bone

Paget's disease is a metabolic bone disease characterized by abnormalities of bone turnover, structure and architecture. The disease is of unknown aetiology, although both genetic and environmental factors have been implicated. Treatment is indicated for patients with active disease and currently bisphosphonates are the first-choice management option.

Osteosarcoma over the age of forty

The European Musculo Skeletal Oncology Society (EMSOS) has carried out a retrospective review of patients over the age of 40 years with osteosarcoma. 481 patients from 12 centres or multicentric groups were included. 42 patients had osteosarcoma arising in Paget's disease, median survival was 9 months. Patients with axial or metastatic tumours also did badly whilst 41 patients with radiation-induced osteosarcoma had a prognosis paralleling conventional osteosarcoma matched for patient age and site of the tumour. 238 patients had high grade non-metastatic osteosarcoma and had a survival of 46% at 5 years. Older patients had less chemotherapy and fared worse. Osteosarcoma in the elderly is a curable condition and warrants intensive treatment with chemotherapy and surgical resection.

From the archives of the AFIP. Radiologic spectrum of Paget disease of bone and its complications with pathologic correlation

Paget disease of bone is a common disorder affecting approximately 3%-4% of the population over 40 years of age. The pathologic abnormality in Paget disease is excessive and abnormal remodeling of bone. Three pathologic phases have been described: the lytic phase (incipient-active), in which osteoclasts predominate; the mixed phase (active), in which osteoblasts cause repair superimposed on the resorption; and the blastic phase (late-inactive) in which osteoblasts predominate. Radiographic appearance of Paget disease reflects these pathologic changes and is often characteristic. Initially, there is osteolysis, particularly affecting the skull (osteoporosis circumscripta) and subchondral long bones, with subsequent development of trabecular and cortical thickening and enlargement of bone in the mixed phase of the disease. Finally, areas of sclerosis may develop in the blastic phase. Frequent sites of involvement include the skull (25%-65% of cases), spine (30%-75%), pelvis (30%-75%), and proximal long bones (25%-30%). Bone scintigraphy typically demonstrates marked increased uptake of radionuclide in all phases of Paget disease. Computed tomography and magnetic resonance imaging often show changes similar to those seen radiographically in noncomplicated Paget disease with maintenance of yellow marrow. Complications of Paget disease include the effects of osseous weakening (deformity and fracture), arthritis, neurologic symptoms, and neoplastic involvement. Sarcomatous transformation is the most feared complication, occurring in approximately 1% of cases, and is seen on images as focal bone destruction extending through the cortex with an associated soft-tissue mass. Recognition of the radiologic spectrum of the appearances of Paget disease usually allows prospective diagnosis and differentiation of its associated complications, which helps guide therapy and improve patient management.

Diagnosis and treatment of Paget's disease of bone

Paget's disease of bone (also known as osteitis deformans) is a nonmalignant disease involving accelerated bone resorption followed by deposition of dense, chaotic, and ineffectively mineralized bone matrix. The origin of the disease is unknown, and it is frequently asymptomatic; however, the patient may present with symptoms depending on the bones involved. The most common symptom is pain in the affected bone; neurologic, hearing, vision, cardiac, and oncologic complications are possible. Diagnosis is primarily made by radiographs. Bisphosphonates are the most common treatment.

Osseo-integration in Paget's disease: the bone-anchored hearing aid in the rehabilitation of Pagetic deafness

The first report of a patient with gross Paget's disease and progressive hearing loss who successfully underwent hearing rehabilitation with an osseo-integrated hearing aid is presented. The otological manifestations of Paget's disease and the principles of osseo-integration are discussed. The use of a bone-anchored hearing aid (BAHA) in selected patients with Paget's disease can provide useful amplification and hearing rehabilitation.

Paget's disease of the spine and its management

A review of the literature was conducted to study the pathomechanics by which Paget's Disease of bone (PD) alters the spinal structures that result in distinct spinal pathologic entities such as pagetic spinal arthritis, spinal stenosis, and other pathologies, and to assess the best treatment options and available drugs. The spine is the second most commonly affected site with PD. About one-third of patients with spinal involvement exhibit symptoms of clinical stenosis. In only 12-24% of patients with PD of the spine is back pain attributed solely to PD, while in the majority of patients back pain is either arthritic in nature or a combination of a pagetic process and coexisting arthritis. Neural element dysfunction may be attributed to compressive myelopathy by pagetic bone overgrowth, pagetic intraspinal soft tissue overgrowth, ossification of epidural fat, platybasia, spontaneous bleeding, sarcomatous degeneration and vertebral fracture or subluxation. Neural dysfunction can also result from spinal ischemia, when blood is diverted by the so-called "arterial steal syndrome". Because the effectiveness of pharmacologic treatment for pagetic spinal stenosis has been clearly demonstrated, surgical decompression should only be instituted after failure of antipagetic medical treatment. Surgery is indicated as a primary treatment when neural compression is secondary to pathologic fractures, dislocations, spontaneous epidural hematoma, syringomyelia, platybasia, or sarcomatous transformation. Since, in the majority of cases with pagetic spinal involvement, there are also coexisting osteoarthritic changes, antipagetic medical treatment alone may be disappointing. Therefore, one must be careful before attributing low back pain to PD alone. Five classes of drugs are available for the treatment of PD: bisphosphonates, calcitonins, mithramycin (plicamycin), gallium nitrate, and ipriflavone. Bisphosphonates are the most popular, and several forms have been investigated, but only the following forms have been approved for clinical use: disodium etidronate, clodronate, aledronate, risedronate, neridronate, pamidronate, tiludronate, ibadronate, aminohydroxylbutylidene bisphosphonate, olpadronate, and zoledronate. Several of these forms are still under investigation.

Paget's disease of the elderly

Paget's disease of bone affects 10% of those surviving to the eighth decade of life. Relatively easy to diagnose, treatment decisions are more complex. Surgery and immobilization present unique challenges often requiring prophylaxis to prevent activation/exacerbation of the disease.

Sarcomatous transformation of the orbit in a patient with Paget's disease

OBJECTIVE

To report the clinical and pathologic features of sarcomatous transformation of the skull with involvement of the orbit, in Paget's disease.

DESIGN

Interventional case report.

PARTICIPANT

An 83-year-old woman with Paget's disease who experienced progressive proptosis of the left eye.

INTERVENTION

Fine-needle aspiration biopsy of the orbital mass.

RESULTS

Cytologic examination revealed round to oval malignant cells with wispy cytoplasm, consistent with the diagnosis of sarcoma. The patient died shortly after institution of orbital radiation therapy and systemic steroid therapy.

CONCLUSIONS

Proptosis related to Paget's disease is uncommon, and only rarely is it a result of sarcomatous transformation. Sarcomatous transformation of the skull involving the orbit should be included in the differential diagnosis of progressive proptosis in patients with Paget's disease.

Goals of treatment for Paget's disease of bone

The goals of treatment of Paget's disease must be readdressed in the context of the availability of potent bisphosphonate compounds, including pamidronate and, more recently, alendronate and risedronate. These agents differ from the traditional mainstays of therapy, salmon calcitonin and etidronate, in several respects. First, they achieve a reduction in the elevated indices of pagetic bone turnover of about 80%, in contrast with the 50% reduction seen with the older agents. Second, a majority of patients (in the range of 50-75%, depending on the series) achieve biochemical remission, and the duration of remission may exceed 1 year or more after a single course of therapy. Third, with the newer bisphosphonates the quality of newly forming bone after successful treatment is lamellar in appearance (as was the case with etidronate) but there is no clinically significant mineralization abnormality associated with these more recent agents. With prior therapies, the primary goal of treatment was to relieve symptoms. In the absence of complete suppression of abnormal turnover, disease progression was not completely halted in many patients, increasing the risk of long-term complications. The characteristics of the newer agents, however, suggest that in those patients who achieve remission there is a possibility, albeit not yet proven, of arresting progression and reducing the risk of later complications. Many patients have no symptoms at presentation but have active disease at locations where progression could cause bone enlargement and deformity over time. These patients may be considered to be at increased risk of future complications if untreated. Thus, it is recommended that such individuals receive therapy with a potent bisphosphonate with the goal of attaining normal (or near normal) biochemical indices after initial treatment and/or retreatment. Patients should be followed with measurement of serum alkaline phosphatase every 4-6 months after a course of therapy, and retreatment is suggested when indices rise above the upper limit of normal or by 25% above the previous nadir. The uncommon possibility of secondary resistance to a given agent after more than one treatment course should be assessed in all patients.