paget's disease: uncommon presentations

PAGET'S DISEASE: UNCOMMON PRESENTATIONS Timothy E. Moore, M.D., Mary H. Kathol, M.D., and Georges Y. El-Khoury, M.D.

Department of Radiology The University of Iowa Hospitals and Clinics Iowa City, IA 52242. INTRODUCTION There are numerous accounts describing the classic features of Paget's disease, dating back to 1876 when Sir James Paget presented his meticulous description to the Royal Medical Chirurgical Society of London9. The aim of this paper is to bring attention to some of the lesser well known radiographic features of this disorder. PATIENTS AND METHODS Clinical histories and radiographs of patients with unusual aspects of Paget's disease were retrospectively reviewed. The cases were chosen from the Middlemore Hospital Bone Tumor Registry and Film Museum in Auckland, New Zealand and from the University of Iowa Hospitals and Clinics. Representative cases were chosen to demonstrate features of unusual sites, bone to bone progression, post-immobilization lysis and metastases to Pagetic bone.

RESULTS Unusual Sites Hand films of six patients with Paget's disease of the phalanges were reviewed. Although the historical information for some of these patients is scanty, hand lesions were incidental findings. Paget's disease in the hand has only occasionally been reported. The majority of cases have been in the proximal phalanges and occasionally the middle phalanges" 3'4. Five of our cases involved proximal phalanges; one occurred in a middle phalanx. Five showed typical appearances of moderately advanced blastic Paget's disease with thickening of the cortex, coarsening of trabeculae, and a generalized increase in bone density (Fig. la). Another was in the proximal phalanx of the thumb and demonstrated less advanced changes of mixed lytic and blastic Paget's disease of the proximal and ventral aspects of the bone (Fig. lb). The Pagetic changes in phalanges are virtually identical to those seen in larger long bones. Yet, because of the infrequency of Paget's disease in the hands, the correct diagnosis may not always be considered. Another unusual site is the patella5'8. The patient whose radiograph is illustrated in Figure 2 experienced sudden knee pain when walking down stairs and was found to have a pathologic fracture of the lower pole of the patella through moderately advanced Paget's disease.

Figure 1A

Figure lB Figure 1 Paget's disease in phalanges. (la) Typical thickened cortices, coarsened trabeculae, increased density, and generalized enlargement of the proximal phalanx in established blastic Paget's disease in an as'ymptomatic 58 year old woman. (lb) Less advanced changes in the proximal phalanx of the thumb with the lytic front progressing diagonally across the bone and not yet affecting the distal dorsolateral aspect. The blastic phase has already started at the base. This was an incidental finding in a 62 year old man with symptomatic Paget's disease in his femur.

In additiop to unusual bones affected by Paget's disease, there are unusual sites within bones. When long bones are involved with Paget's disease, the process typically starts at one end and progresses through the shaft until the

Figure 2 Pathologic fracture through the lower pole of the patella secondary to Paget's disease.

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entire bone is involved8. There have been occasional reports of Paget's disease starting in the mid shaft and extending towards the ends8 10. Such a case is illustrated in Figure 3. Although polyostotic Paget's disease is very common, involvement of two separate parts within the same bone is uncommon8. Figure 4 shows Paget's disease in the proximal and distal tibia with a section of the intervening shaft still unaffected. Typical V-shaped fronts are seen advancing towards one another.

Progression from Femur to Tibia Despite the frequent polyostotic nature of Paget's disease, the process should not cross joints. This rule does not, however, apply after the joint has been surgically fused. The patient whose films are illustrated in Figure 5 developed degenerative disease of his knee secondary to advanced Paget's disease of the femur. There was no Paget's disease in the tibia until after arthrodesis of the knee joint, when the Pagetic process could be seen extending across the fusion and into the previously unaffected tibia.

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Figure 3B

Figure 3 Diaphyseal Paget's disease. (3a) 1941. Mainly lytic phase of Paget's disease but with some coarsened trabeculae and enlargement of the affected segment. (3b) 1952. A lytic front of Paget's disease is progressing distally through the lower tibial shaft. The proximal lytic front has encompassed the whole proximal tibia. (3c) 1967. The entire tibia has been replaced with blastic Pagetic bone.

Figure 5A

Figure 5B

Figure 5 Bone to bone progression. (5a) Advanced Paget's disease is seen in the femur. The tibia is unaffected. (5b) Some years later the Pagetic process has crossed the arthrodesis and is advancing down the tibia. (Courtesy of Prof. R. Gibson, Christchurch, New Zealand) Figure 4 Two foci of Paget's disease in one bone. V-shaped lytic Pagetic fronts are seen approaching one another from either end of the tibia.

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Post-Immobilization Lysis Despite the markedly increased turnover of bone in active Paget's disease, serum calcium and phosphate are usually normal. However, after fractures or prolonged immobilization, urinary calcium excretion may be increased and rarely hypercalcemia may be encountered7. This is due to an increase in bone resorption in excess of bone formation. Radiographs of two patients with proximal tibial Paget's disease and tibial shaft fractures were reviewed. In both patients, advanced osteopenia developed proximal to the fracture and involved only the Pagetic bone. In the case illustrated in Figure 6, a biopsy was taken from the tibia in the center of the lytic region eight weeks after the fracture occurred. The histologic appearances confirmed the generalized osteoclastic resorption of Pagetic bone with no evidence of infection or neoplasm. This patient's

Paget's Disease: Uncommon Presentations

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Figure 7B

Figure 7A

Figure 6A

Figure 6B

Figure 6: Post-immobilization lysis. (6a) Acute fractures of the tibial and fibular shafts. Note the thickened anterior cortex of the tibia. (6b) Eight weeks after the fracture, there appears to be a destructive lesion of the proximal tibia with a well demarcated oblique junction between abnormal and normal bone. serum calcium levels remained within normal limits. His alkaline phosphatase level was double the normal value. In both cases, the differentiation from reflex sympathetic dystrophy or disuse osteoporosis was easy because the Pagetic bone occurred proximal to the fracture sites. The preservation of essentially normal bone density distal to the fractures would exclude these forms of acute osteoporosis. Metastases to Pagetic Bone It has been suggested that the increased vascularity of bone affected by Paget's disease makes it more susceptible to hematogenous metastases6. Blastic metastases, particularly prostatic carcinoma metastatic to the pelvis and lumbar spine, can sometimes be confused with blastic Paget's disease2. The tendency for Paget's disease to affect specific bones and to produce coarse trabeculae, thickened cortices, and expanded bone, allows differentiation between blastic metastases and Pagetic bone. However, metastatic disease superimposed upon Paget's disease can cause a greater diagnostic dilemma. An example is a 78 year old man with pain in his mid back who was found to have radiographic changes of Paget's disease in the first lumbar vertebra in addition to loss of the left pedicles of T12 and Li (Fig. 7a,b). On computerized tomography, Li showed the typical thickened cortex, coarse trabeculation, and well corticated small rounded lytic regions of Paget's disease. In addition to destruction of the left pedicle associated with a soft-tissue mass, there were also other lytic

Figure 7C

Figure 7: Metastases to Pagetic bone. (7a,b) AP and lateral lumbar spine radiographs demonstrate the typical "picture frame" appearance of Paget's disease of Li and the not well defined right Li pedicle. (7c) CT through Li shows thickened cortices and coarsened blastic appearances typical of Paget's disease. In addition, there is a metastatic lesion partially destroying the right pedicle and completely destroying the left pedicle. There is also a soft tissue mass adjacent to the left pedicle (arrow).

lesions showing ill-defined margins suggestive of a more aggressive process (Fig. 7c). A biopsy confirmed the coexistence of Paget's disease of bone and a poorly differentiated metastatic prostate carcinoma. In this case, the radiologic diagnosis was made easier by the purely lytic metastasis. The cases presented demonstrate uncommon presentations of Paget's disease. Because we are unaccustomed to seeing Paget's disease in unusual sites such as the hands and patellae, the correct diagnosis may not be considered. The diagnosis may also be overlooked if it presents in the diaphysis or two separate sites within a frequently affected bone 10. The phenomenon of post-immobilization lysis in Paget's disease is well known, yet it does not usually Volume 9

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T E. Moore, M. H. Kathol, G. Y El-Khoury produce the dramatic changes seen in Figure 6. This case was initially thought to be an aggressive neoplastic process, but review of the initial films revealed considerable thickening of the anterior cortex of the tibia typical of blastic Paget's disease. Because both Paget's disease and bone metastases are found more in the older age group, these conditions can be expected to occasionally co-exist, irrespective of the susceptibility of Pagetic bone for metastases. Blastic metastatic deposits are usually round or oval lesions which do not resemble Paget's disease. However, widespread blastic metastases can be more confusing. They are generally more symmetrically distributed than Paget's disease and should not coarsen the trabeculae or increase the size of affected bones8. Lytic metastases do not usually cause confusion with Paget's disease although occasionally a large metastasis can mimic the lytic phase of Paget's disease8 (Fig. 8). .~~~~~~~~~~~~~~~~

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Figure 8 Large solitary lytic metastasis to proximal femur from breast carcinoma The V-shaped inferior margin (arrow) gave the mistaken impression of lytic Paget's disease.

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BIBLIOGRAPHY 1 Barry, H. C.: Paget's Disease of Bone. E. & S. Livingstone Ltd, Edinburgh and London, 1969. 2- Frame, B., and Marel, M.: Paget's Disease: A Review of Current Knowledge. Radiology, 141:21-24, 1981. '- Friedman, A. C.; Orcutt, J.; and Madewell, J. E.: Paget Disease of the Hand: Radiographic Spectrum. AJR, 138:691693, 1982. 4- Haverbush, I.J., and Wilde, A. H. The Hand in Paget's Disease of Bone: Report of Two Cases. J Bone and Joint Surg. (Am), 54-A: 173-175, 1972. 5- Heuck, H. and Buck, J.: Rare Localizations of Paget's Disease in the Skeleton. Radiology, 24:422-427, 1984. 6. Jacobson, H. G., and Siegelman, S.S.: Some Miscellaneous Solitary Bone Lesions. Semin. Roentgenol., 1:314335, 1966. 7- Krane, S.M.: Paget's Disease of Bone. In Harrison's Principles of Internal Medicine, 11th Edition. Editors Braunwald, E., Isselbachet, K.J., Petersdorf, R. G., et al. McCraw-Hill, New York, 1987, pp. 1900-1902. 8- Levine, R. B.; Rae, V. M.; Karasnick, D.; and Greenberg, S. B.: Paget Disease: Unusual Radiographic Manifestations. CRC Crit. Rev. Diagn. Imaging, 25:209-232, 1986. 9 Paget, J.: On a Form of Chronic Inflammation of Bones (Osteitis Deformans). Med. Chir. Trans., 60:37, 1877. 10. Schubert, F.; Siddle, K.J.; and Harper, J. S.: Diaphyseal Paget's Disease: An Unusual Finding in the Tibia. Clinical Radiology, 35:71-74, 1984.