Paget Disease Imaging

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Paget disease of bone (osteitis deformans) is a metabolic disorder characterized by abnormal osseous remodeling. Sir James Paget first described Paget disease in 1877 as a chronic inflammatory remodeling disease of bones. He termed the condition osteitis deformans. ^{[1, 2, 3]}  Paget disease of bone is caused by a localized increase in osteoclastic and osteoblastic activity and can progress to involve the entire bone. Deformed, enlarged bones is a common feature, especially in weight-bearing areas. ^[4]  Genetic factors play an important role in pathogenesis, with evidence that susceptibility may be determined by variants in or near genes that regulate osteoclast function. ^[5]

Paget disease is depicted in the images below.

Paget disease evolves through 3 stages: (1) an early lytic or hot phase; (2) an intermediate or mixed phase; and (3) a final or cold phase, marked by dense bone formation

Paget disease rarely is diagnosed in the initial lytic phase. At this early point of the disease, osteoclastic activity is predominant. Paget disease usually begins at the end of a bone, except when it occurs in the tibia. A characteristic sharply demarcated zone of osteolysis may begin in the subcortical bone and advance along the diaphysis. Osteoblastic activity lags behind; thus, radiolucent fibrous tissue replaces normal bone.

The intermediate or mixed phase reveals evidence of osteolytic and disorganized osteoblastic activity. New bone forms abnormally and demonstrates characteristically coarsened trabecula and cortical thickening in the cancellous and compact bone, respectively. Characteristic intracytoplasmic inclusions may be observed microscopically, supporting evidence for the viral etiology theory.

The final or cold phase demonstrates less evidence of continual osseous remodeling. Previously laid down woven bone is converted to dense lamellar bone. Histologic features of disorganized bone are prominent. The intersecting lines of remodeled bone have a characteristic mosaic pattern histologically.

Insufficiency fractures in patients with Paget disease may present with pain that can last up to several weeks. If pain is focal and severe, it may be a sign of an impending, complete fracture, and radiographic evaluation is warranted. Insufficiency fractures most frequently affect the femur and tibia. Involvement in critical weight-bearing locations may lead to fracture or severe secondary arthritis. ^{[6, 7, 8]} See the images below.

The radiographic findings of Paget disease are diagnostic in many patients. ^{[9, 10, 11]} The lytic stage most commonly is observed in the skull and long bones. The typical appearance in the long bones is osteolysis, which begins in the epiphysis and advances along the diaphysis. Trabecular coarsening and distortion and cortical thickening are observed in the sclerotic phase, typically involving the axial skeleton.

Radiographic findings in Paget disease often are pathognomonic, particularly in the lytic phase. However, given the variable imaging appearance of Paget disease in different stages, as well as the many different bones involved, the differential diagnosis may vary substantially among patients.

In the skull, the lytic phase (osteoporosis circumscripta) typically involves the frontal or occipital bones and progresses to a mixed pattern with multifocal sclerotic patches in the intermediate stage of the disease, referred to as a cotton wool appearance. ^[12] See the images below.

The vertebral bodies typically become enlarged with a prominent cortical margin (picture frame vertebrae) or become densely sclerotic, mimicking lymphoma or metastatic disease (ivory vertebra). See the images below.

In the pelvis, typical findings include thickening of the iliopectineal line in early stages, progressing to patchy sclerosis and lucency in later stages. See the image below.

Weakening of the pagetic acetabular bone may lead to protrusio acetabuli and insufficiency fracture. See the image below.

In the long bones, early involvement consists of lysis of the subarticular bone, which advances along the diaphysis with the characteristic shape of a blade of grass. Long bones are affected first in the epiphyseal region, with the exception of the tibia, where Paget disease frequently begins in the tubercle.

Later stages of disease show development of enlarged, sclerotic, deformed bones with thickened coarse trabeculae. The weakened femur and tibia eventually may become bowed under the stress of weight bearing. Insufficiency fractures may occur, characteristically involving the convex cortical surface. Conversely, Looser zones of osteomalacia typically occur on the concave cortical surface. See the images below.

Development of secondary sarcoma in pagetic bone is the most lethal complication of Paget disease, occurring in 1% or fewer of patients with Paget disease (see the image below). These sarcomas are aggressive and may be multicentric. Short-term interval follow-up and/or cross-sectional imaging may prevent diagnostic errors and initiate prompt attention to a newly developing lesion. ^{[13, 14, 15]}

Cross-sectional MRI and CT demonstrate the altered bone structure seen in Paget disease, such as coarsened trabeculae, thickened cortices, and bone hypertrophy. Findings that are present on plain radiography are often better displayed on CT. MRI does not depict the changes in mineralization as well as traditional radiography or CT. MRI, however, can show alterations in marrow characteristics that can mirror the pathologic changes occurring during the course of the disease. Thus, earlier in the disease, marrow signal can be normal or hypervascular, while later changes can show fatty replacement of the marrow. ^[16]

The anatomy is well demonstrated by cross-sectional imaging in complex structures, such as the spine, where spinal or nerve root compression may be an issue. Cross-sectional imaging also helps delineate the pathology in complicated Paget disease, which includes nerve or spinal cord compression, as well as basilar invagination at the skull base and osseous encroachment involving cranial nerve foramina.

Secondary sarcomatous development also is better evaluated with cross-sectional imaging. Additionally, should biopsy be indicated for the diagnosis of sarcoma, CT typically is the guidance modality of choice. See the images below.

In a study of the use of MRI in patients with Paget disease of the spine, MRI showed a mixed pattern of increased/decreased T1 signal (fine trabecular or coarse) of the vertebral bodies. Band-like decreased T1 and T2 signal of the endplates was also present, correlating with the mixed osteolytic and blastic phase of the disease. Subtle or conspicuous picture-frame appearance was also noted. In most cases, there was expansion of the vertebral body and/or posterior elements/spinous process. ^[17]

See the images below.

Skeletal scintigraphy is useful. Radionuclide bone scans are more sensitive than radiographs for the diagnosis of Paget disease. Additionally, bone scans help survey the different sites of involvement with polyostotic disease.

Characteristically, a marked uptake of radiopharmaceutical in the involved bones is observed. However, late-stage involvement may not reveal intense radiopharmaceutical uptake, and osteoporosis circumscripta may demonstrate only a peripheral rim of increased uptake. Scintigraphy tends to follow the physiologic activity of disease and may monitor treatment.

Polyostotic Paget disease often can be distinguished from multiple metastatic lesions, although occasional difficulties occur. Perform radiographic correlation when this situation arises. Furthermore, the diagnosis of fracture or sarcoma may be challenging, often requiring multimodality correlation. See the images below.

Paget J. On a form of chronic inflammation of bones (osteitis deformans). Med Chir Tr. 1877. 60:37.

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Tan A, Ralston SH. Clinical presentation of Paget’s disease: evaluation of a contemporary cohort and systematic review. Calcif Tissue Int. 2014 Nov. 95(5):385-92. [Medline].

Singer FR. Bone Quality in Paget’s Disease of Bone. Curr Osteoporos Rep. 2016 Mar 4. [Medline].

Vallet M, Ralston SH. Biology and Treatment of Paget’s Disease of Bone. J Cell Biochem. 2016 Feb. 117 (2):289-99. [Medline].

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Harrington KD. Surgical management of neoplastic complications of Paget’s disease. J Bone Miner Res. 1999 Oct. 14 Suppl 2:45-8. [Medline].

Zuffetti F, Bianchi F, Volpi R, Trisi P, Del Fabbro M, Capelli M, et al. Clinical application of bisphosphonates in implant dentistry: histomorphometric evaluation. Int J Periodontics Restorative Dent. 2009 Feb. 29(1):31-9. [Medline].

Guañabens N, Rotés D, Holgado S, Gobbo M, Descalzo MÁ, Gorordo JM, et al. Implications of a new radiological approach for the assessment of Paget disease. Calcif Tissue Int. 2012 Dec. 91(6):409-15. [Medline].

Farpour F, Tehranzadeh J, Donkervoort S, Smith C, Martin B, Vanjara P, et al. Radiological features of Paget disease of bone associated with VCP myopathy. Skeletal Radiol. 2012 Mar. 41(3):329-37. [Medline].

Ferris-James DM, Iuanow E, Mehta TS, Shaheen RM, Slanetz PJ. Imaging approaches to diagnosis and management of common ductal abnormalities. Radiographics. 2012 Jul-Aug. 32(4):1009-30. [Medline].

Sandford A, Jawad AS. The ‘cotton wool’ sign in paget’s disease of the skull. QJM. 2016 Feb. 109 (2):131. [Medline].

Smith J, Botet JF, Yeh SD. Bone sarcomas in Paget disease: a study of 85 patients. Radiology. 1984 Sep. 152(3):583-90. [Medline].

Deyrup AT, Montag AG, Inwards CY, Xu Z, Swee RG, Krishnan Unni K. Sarcomas arising in Paget disease of bone: a clinicopathologic analysis of 70 cases. Arch Pathol Lab Med. 2007 Jun. 131(6):942-6. [Medline].

Sharma H, Mehdi SA, MacDuff E, Reece AT, Jane MJ, Reid R. Paget sarcoma of the spine: Scottish Bone Tumor Registry experience. Spine (Phila Pa 1976). 2006 May 20. 31(12):1344-50. [Medline].

Dohan A, Parlier-Cuau C, Kaci R, Touraine S, Bousson V, Larédo JD. Vertebral involvement in Paget’s disease: morphological classification of CT and MR appearances. Joint Bone Spine. 2015 Jan. 82 (1):18-24. [Medline].

Morales H. MR Imaging Findings of Paget’s Disease of the Spine. Clin Neuroradiol. 2015 Sep. 25 (3):225-32. [Medline].

Paul A Cripe, MD Resident Physician in Diagnostic Radiology, Department of Radiology, Naval Medical Center San Diego

Paul A Cripe, MD is a member of the following medical societies: Alpha Omega Alpha, American College of Radiology, Radiological Society of North America

Disclosure: Nothing to disclose.

Charles Egan, DO Lieutenant Commander, US Navy; Staff Neuroradiologist, MRI Director, Naval Hospital Camp Lejeune

Charles Egan, DO is a member of the following medical societies: American College of Radiology, American Medical Association, American Roentgen Ray Society, American Society of Neuroradiology, Radiological Society of North America

Disclosure: Nothing to disclose.

Bernard D Coombs, MB, ChB, PhD Consulting Staff, Department of Specialist Rehabilitation Services, Hutt Valley District Health Board, New Zealand

Disclosure: Nothing to disclose.

Wilfred CG Peh, MD, MHSc, MBBS, FRCP(Glasg), FRCP(Edin), FRCR Clinical Professor, Yong Loo Lin School of Medicine, National University of Singapore; Senior Consultant and Head, Department of Diagnostic Radiology, Khoo Teck Puat Hospital, Alexandra Health, Singapore

Wilfred CG Peh, MD, MHSc, MBBS, FRCP(Glasg), FRCP(Edin), FRCR is a member of the following medical societies: American Roentgen Ray Society, British Institute of Radiology, International Skeletal Society, Radiological Society of North America, Royal College of Physicians, Royal College of Radiologists

Disclosure: Nothing to disclose.

Felix S Chew, MD, MBA, MEd Professor, Department of Radiology, Vice Chairman for Academic Innovation, Section Head of Musculoskeletal Radiology, University of Washington School of Medicine

Felix S Chew, MD, MBA, MEd is a member of the following medical societies: American Roentgen Ray Society, Association of University Radiologists, Radiological Society of North America

Disclosure: Nothing to disclose.

Leon Lenchik, MD Program Director and Associate Professor of Radiologic Sciences-Radiology, Wake Forest University Baptist Medical Center

Leon Lenchik, MD is a member of the following medical societies: American College of Radiology, American Roentgen Ray Society, Radiological Society of North America

Disclosure: Nothing to disclose.

Mitchell J Kline, MD Consulting Staff, Department of Diagnostic Radiology, University of Louisville, Clark Memorial and Floyd Memorial Hospitals

Mitchell J Kline, MD is a member of the following medical societies: Alpha Omega Alpha, American College of Radiology, American Roentgen Ray Society, Radiological Society of North America, and Society of Skeletal Radiology

Disclosure: Nothing to disclose.

The views expressed in this presentation are the authors’ and do not necessarily reflect the official policy or position of the Department of the Navy, Department of Defense, or the U.S. Government.

Paget Disease Imaging

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