Paramyxoviruses and Paget's disease

Failure to detect measles virus ribonucleic acid in bone cells from patients with Paget's disease

BACKGROUND

Paget's disease is a condition of focal accelerated bone turnover. Electron-microscopy investigations of osteoclasts from pagetic lesions have identified nuclear inclusion bodies that have a similar appearance to viral nucleocapsid particles. Subsequently, RNA from several paramyxoviruses has been detected in pagetic tissue, and it was suggested that these viruses, in particular measles, might play a role in the etiology of Paget's disease. We have tested for measles virus sequences in osteoblasts and bone marrow cells collected from pagetic lesions and healthy bone.

METHODS

Bone and bone marrow samples were taken from Paget's patients and control subjects, and cells were cultured from each of these tissues. RNA was extracted from 13 osteoblast cultures and 13 cultures of bone marrow cells derived from pagetic lesions, and from 26 and 23 control osteoblast and bone marrow cultures, respectively. These samples were sourced from 22 patients with Paget's disease and 31 controls. RT-PCR-nested PCR amplification was used for the detection of the genes for the measles nucleocapsid and matrix proteins.

RESULTS

Measles virus sequences were not detected in any of the pagetic or control samples. However, measles virus sequences were identified in samples of a measles virus culture isolate included as a positive control, and in a brain sample from a patient with subacute sclerosing panencephalitis, a condition associated with chronic measles infection.

CONCLUSION

The results of the study do not support the hypothesis that measles virus plays a role in the pathogenesis of Paget's disease.

Placement and restoration of dental implants in a patient with Paget's disease in remission: literature review and clinical report

Paget's disease is a disorder of bone that results in the replacement of normal bone with highly vascularized, low density bone. The diminished bone quality associated with Paget's disease is a relative contraindication to the use of dental implants, as it interferes with achievement of osseointegration. There is no current literature on the success of dental implants in patients with Paget's disease. Furthermore, there is no current literature on dental implant success in patients with remissive Paget's disease or in bone that appears to be unaffected by the disease in patients with Paget's. This case report follows the treatment of a patient with a partially edentulous maxilla and mandible (ACP PDI Classification III) who presented with remissive Paget's disease. Definitive treatment included the placement of four endosseous implants used to retain full veneer crowns. Despite the radiographic appearance of adequate bone quality, upon surgical placement it was discovered that the quality of bone was poor, yet implant survival was achieved through careful surgical management and rigid splinting of some of the endosseous implants.

Osteosarcoma arising in Paget's disease of the mandible

Although osteosarcoma is a well-known complication of Paget's disease of bone, it uncommonly develops in the jaw bones. We present an osteosarcoma arising in Paget's disease of the mandible with unique features of a normal serum alkaline phosphatase level, and histologic features of telangiectatic change in the osteosarcoma and association with cemento-osseous dysplasia. Sixteen reported cases of osteosarcoma arising in Paget's disease of the jaw bones (OPJ) are also reviewed and compared to osteosarcoma arising in Paget's disease occurring in the entire skeleton (OPS) and osteosarcoma arising de novo in the jaw bones (OJ). Females are more commonly involved in OPJ in contrast to a male predominance in OPS and OJ. OPJ also has a distinctively higher percentage involving blacks compared to OPS. The prognosis of OPJ is poor, with 69% of patients dying within two years after diagnosis. Early recognition, early and aggressive treatment are important to improve the prognosis and are hence emphasized.

Bilateral enophthalmos associated with paget disease of the skull: a case report

PURPOSE

To describe a case of familial Paget disease of bone associated with bilateral enophthalmos and mild exposure keratopathy.

METHODS

Case report and literature review.

RESULTS

A 71-year-old woman with familial Paget disease of bone had a long history of "receding eyes," headaches, and moderately dry eyes. She had bilateral enophthalmos with mild exposure keratopathy. Radiologic and endocrinologic investigation confirmed Paget disease of bone affecting the skull.

CONCLUSIONS

Enophthalmos in association with Paget disease of bone is rare and is likely to result from differential expansion of the cranium compared with the orbital bones.

Sequence analysis of measles virus nucleocapsid transcripts in patients with Paget's disease

It has been debated for almost 30 years whether Paget's disease of bone results from paramyxoviral infection of osteoclasts (OCs). Paramyxoviral-like nuclear inclusions are found in OCs from patients with Paget's disease, and measles virus (MV) or canine distemper virus (CDV) messenger RNA (mRNA) transcripts have been detected by in situ hybridization in bone cells from pagetic lesions. Furthermore, immunocytochemical studies have shown the presence of several paramyxoviral species in OCs from patients with Paget's disease. However, others have been unable to detect paramyxoviral transcripts in bone samples from patients with Paget's disease or marrow cultures from involved sites of patients with Paget's disease. Furthermore, no one has been able to isolate an infectious virus from pagetic bone samples or marrow cells from patients with Paget's disease, and a full-length viral gene has not been sequenced from pagetic samples. In this study, we have obtained the full-length sequence for the MV nucleocapsid (MVNP) gene in bone marrow from an involved site from a patient with Paget's disease and more than 700 base pairs (bps) of MVNP sequence in 3 other patients with Paget's disease. These sequences were undetectable in four normal marrow samples studied simultaneously. The sequences from the patients contained multiple mutations that differed from the Edmonston strain MVNP gene. These findings are consistent with the presence of a chronic MV infection in affected sites from these patients with Paget's disease.

Paget disease of bone: mapping of two loci at 5q35-qter and 5q31

Paget disease of bone is characterized by focal increases of the bone-remodeling process. It is the second most common metabolic bone disease after osteoporosis. Genetic factors play a major role in the etiology of Paget disease of bone, and two loci have been mapped for the disorder: PDB1 and PDB2. The gene(s) causing the typical form of the disorder remains to be characterized. To decipher the molecular basis of Paget disease of bone, we performed genetic linkage analysis in 24 large French Canadian families (479 individuals) in which the disorder was segregating as an autosomal dominant trait. After exclusion of PDB2, a genomewide scan was performed on the three most informative family nuclei. LOD scores >1.0 were observed at seven locations. The 24 families were then used to detect strong evidence for linkage to chromosome 5q35-qter. Under heterogeneity, a maximum LOD score of 8.58 was obtained at D5S2073, at straight theta= .1. The same characteristic haplotype was carried by all patients in eight families, suggesting a founder effect. A recombination event in a key family confined the disease region within a 6-cM interval between D5S469 and the telomere. The 16 other families, with very low conditional probability of linkage to 5q35-qter, were further used, to map a second locus at 5q31. Under heterogeneity, a maximum LOD score of 3.70 was detected at D5S500 with straight theta=.00. Recombination events refined the 5q31 region within 12.2 cM, between D5S642 and D5S1972. These observations demonstrate the mapping of two novel loci for Paget disease of bone and provide further evidence for genetic heterogeneity of this highly prevalent disorder. It is proposed that the 5q35-qter and 5q31 loci be named "PDB3" and "PDB4," respectively.

Familial Paget's disease of bone: nonlinkage to the PDB1 and PDB2 loci on chromosomes 6p and 18q in a large pedigree

Paget's disease of bone is a common condition characterized by bone pain, deformity, pathological fracture, and an increased incidence of osteosarcoma. Genetic factors play a role in the pathogenesis of Paget's disease but the molecular basis remains largely unknown. Susceptibility loci for Paget's disease of bone have been mapped to chromosome 6p21.3 (PDB1) and 18q21.1-q22 (PDB2) in different pedigrees. We have identified a large pedigree of over 250 individuals with 49 informative individuals affected with Paget's disease of bone; 31 of whom are available for genotypic analysis. The disease is inherited as an autosomal dominant trait in the pedigree with high penetrance by the sixth decade. Linkage analysis has been performed with markers at PDB1; these data show significant exclusion of linkage with log10 of the odds ratio (LOD) scores < -2 in this region. Linkage analysis of microsatellite markers from the PDB2 region has excluded linkage with this region, with a 30 cM exclusion region (LOD score < -2.0) centered on D18S42. These data confirm the genetic heterogeneity of Paget's disease of bone. Our hypothesis is that a novel susceptibility gene relevant to the pathogenesis of Paget's disease of bone lies elsewhere in the genome in the affected members of this pedigree and will be identified using a microsatellite genomewide scan followed by positional cloning.

Absence of measles virus and canine distemper virus transcripts in long-term bone marrow cultures from patients with Paget's disease of bone

The presence of intranuclear inclusions in pagetic osteoclasts with similar characteristics to those seen in some slow viral diseases has lead to the hypothesis that Paget's disease is caused by a similar infection. Bone marrow aspirates from seven patients with hemipelvic Paget's disease were taken from both sides of the pelvis and cultured under identical conditions. RNA was extracted after approximately 2 weeks of culture and reverse transcriptase-linked polymerase chain reaction used to investigate the expression of measles and canine distemper virus RNA. We were unable to detect the presence of measles virus (MV) or canine distemper virus (CDV) transcripts in bone marrow cultures from either affected or unaffected sites in any of our patients. The results of this study do not support a role for MV or CDV in the pathogenesis of Paget's disease of bone.

Paget's disease of bone: indications for treatment and goals of therapy

Paget's disease of bone is a common disorder of unknown etiology characterized by increased bone remodeling and abnormal bone architecture. The pathologic process is initiated by an increase in osteoclast-mediated bone resorption, accompanied by a compensatory increase in bone formation. The increased bone remodeling results in a disorganized mosaic of woven and lamellar bone. This bone is highly vascular and gradually becomes enlarged and structurally weakened. Paget's disease is generally diagnosed in patients older than 40 years of age, usually as an incidental finding. The disease may be monostotic or polyostotic. The pelvis, femur, spine, tibia, skull, and humerus are most commonly involved. Most patients with Paget's disease are asymptomatic. Pain is the most common presenting symptom. Complications of the disease include bowing deformity of the long bones, fracture, and a variety of nerve compression syndromes. Malignant degeneration of Paget's disease is a rare complication. As safer, more effective therapies have become available, the indications for treatment and goals of therapy have changed. The difficult issue that clinicians are currently facing is whether to treat patients with asymptomatic disease. The progressive nature of the disease, the severity of its complications, its potential negative impact on quality of life, and the availability of therapy capable of controlling its activity have led many experts in the field to recommend treatment of asymptomatic patients who have active disease at sites where complications are likely to develop. There are, however, no data to prove that complications can be prevented by decreasing the rate of bone remodeling in Paget's disease, nor any data to define who is at risk for complications. Until more information is available, the management of patients with Paget's disease will continue to be based on clinical observation and theoretical considerations. This review examines the present understanding of Paget's disease, the rationale for the proposed indications for treatment and the goals of therapy.

In situ hybridization and its diagnostic applications in pathology

In situ hybridization (ISH) is a technique by which specific nucleotide sequences are identified in cells or tissue sections. These may be endogenous, bacterial or viral, DNA or RNA. On the basis of research applications, the technique is now being translated into diagnostic practice, mainly in the areas of gene expression, infection and interphase cytogenetics. Diagnostic applications are most often based on short nucleotide sequences (oligomers) labelled with non-isotopic reporter molecules, and sites of binding may be localized by histochemical or immunohistochemical methods. The technique can be applied to routinely fixed and processed tissues; with some targets, it is even possible to obtain hybridization in autopsy material. ISH has been used to detect messenger RNA (mRNA) as a marker of gene expression, where levels of protein storage are low; for example, to confirm an endocrine tumour as the source of excess hormone production. Its application in infectious diseases has to date been mainly in viral infections, such as the typing of human papillomavirus (HPV) or the detection of Epstein-Barr virus by the presence of small nuclear RNAs (EBERs). The expression of mRNAs for histone proteins has been used to detect cells in S phase, and related methods may be applied to detect apoptotic cells. Using probes to chromosome-specific sequences, it is possible to detect aneuploidy, and to document changes in specific chromosomes, which may have prognostic significance in some tumours, such as B-cell chronic lymphatic leukaemia. Using sequence-specific probes, translocations can be identified, such as the t(11;12) of Ewing's sarcoma. This review presents an outline of the technique of in situ hybridization and discusses areas of current and potential diagnostic application.

Paget bone disease involving young adults in 3 generations of a Korean family

Although the etiology of Paget bone disease (PBD) is unknown, increasing evidence implicates a "slow virus" infection of the skeleton, perhaps in genetically predisposed individuals. PBD is rare in Asia. We describe a Korean family with PBD. The propositus noticed bowed limbs at approximately 25 years of age. Radiologic studies made when he was 55 years old revealed essentially panostotic PBD. Serum alkaline phosphatase (ALP) activity and osteocalcin (OC) levels were markedly elevated. An iliac crest specimen showed classic histopathologic changes of PBD. Additionally, palpable swellings were first observed at age 45 years at his occiput, pubic ramus, ileum, and facial bones. They contained numerous multinucleated cells and were originally diagnosed as giant cell tumors. However, we found that, like osteoclasts, these cells expressed considerable tartrate-resistant acid phosphatase activity. These "extraskeletal osteoclastomas" resolved rapidly with dexamethasone treatment. Two daughters, 20- and 24-years-of-age, were discovered by study of his 5 children to have elevated serum ALP activity and OC levels and widespread PBD. Both women, however, are without palpable masses and are asymptomatic. The propositus' father, who died at age 55 years, had similar skeletal deformities beginning at age 20 years, but was not examined. Leukocytopenia was found in the 3 living family members with PBD. There was no evidence for linkage of the PBD to HLA loci. The condition appears to be transmitted as an autosomal dominant trait and is manifest in young adult life. Multicentric extraskeletal osteoclastomas with remarkable sensitivity to dexamethasone treatment appear to be another unusual feature of this family's disorder. In this family, the stimulus for PBD is so great that the PBD is apparent at an early age, affects essentially the entire skeleton, and leads to the formation or extension of osteoclast-like cells into nonosseous tissues (extraskeletal osteoclastomas). This 3-generation kindred in Korea, where PBD is rare, shows a strong clustering of PBD compatible with autosomal dominant inheritance. Leukocytopenia appears to distinguish affected family members, but any role for this abnormality in the pathogenesis of PBD is unclear. Our findings support a heritable diathesis for PBD, perhaps mediated by an immune deficiency.

Paget's disease of bone: clinical, pathogenetic and therapeutic aspects

Paget's disease of bone is a focal disorder of bone remodelling due to abnormally increased osteoclast-mediated bone resorption. It rarely presents before the age of 35 years and its prevalence increases with age affecting 2-5% of the population above 50 years, making Paget's disease the most common skeletal disorder after osteoporosis. Its aetiology is not known but available evidence favours an infection of genetically predisposed individuals with a paramyxovirus. Affected bones change in shape, size and direction causing considerable morbidity but the majority of patients are asymptomatic. In Paget's disease increased bone resorption is tightly linked to increased bone formation which are reflected in the proportional increases in biochemical indices of bone turnover. Because the primary abnormality lies in the osteoclasts, inhibitors of bone resorption are used for its therapy and bisphosphonates are currently the treatment of choice. These decrease bone turnover effectively and their effect lasts after stopping treatment. With available bisphosphonates clinical and biochemical, long-lasting, remissions can be obtained in the majority of patients. Symptomatic disease and preparation for orthopaedic surgery are no longer the only indication for treatment, but asymptomatic patients with localizations at sites likely to induce complications should be considered candidates for bisphosphonate therapy.

Acquired osteosclerosis associated with intravenous drug use and hepatitis C infection

Hepatitis C has recently been recognized as a secondary cause of osteosclerosis; a further example, the first outside of North America, is described. A 37-year-old man with a history of intravenous drug use and known to be hepatitis C antibody positive presented with bone pain. Radiographs and magnetic resonance imaging demonstrated an increase in cortical and trabecular bone that on biopsy was of a normal lamellar pattern but markedly sclerotic. Biochemical markers of bone formation (serum osteocalcin) and resorption (urinary hydroxyproline excretion rate) were both markedly elevated. Pain lessened following administration of pamidronate. Biochemical markers of bone turnover fell towards their reference ranges 12 months after initiating pamidronate therapy but without significant change in bone mineral density. Osteosclerosis is a rare complication of hepatitis C infection, the symptoms of which are controllable with diphosphonate therapy.

Paget's disease of bone and unvaccinated dogs

The etiology of Paget's disease is unknown, but several observations suggest a viral cause. Since canine distemper virus is among those proposed to be a causal agent, we investigated the hypothesis that dog ownership may increase the risk of Paget's disease of bone by means of a case control study. One hundred and fifty patients with Paget's disease and 185 controls were interviewed using a structured questionnaire administered by the same interviewer. Participants were asked about their socioeconomic background and their exposure to pets. The risk of Paget's disease was not significantly increased in individuals. However, ownership of a mongrel dog was associated with a significant increase in risk (OR = 1.6; 95% CI = 1.0-2.4) and the risk increased still further with the ownership of an unvaccinated dog (OR = 2.8; 95% CI = 1.8-4.5). Additionally, ownership of cats and birds excluding dog owners, increased the risk of Paget's disease (OR = 2.5; 95% CI = 1.0-5.0; OR = 2.3; 95% CI = 1.0-5.3, respectively). These data suggest that previous exposure to cats, birds, and dogs unvaccinated for canine distemper may increase the risk of an individual developing Paget's disease of bone.

Histologic and immunocytochemical characterization of canine distemper-associated metaphyseal bone lesions in young dogs following experimental infection

The proximal metaphyses of the humerus of weanling gnotobiotic dogs experimentally infected with canine distemper virus (CDV) were investigated histologically and immunocytochemically between 4 and 41 days after infection. Viral antigen was demonstrated in hematopoietic marrow and bone cells at postinfection day (PID) 5 and PID 7, respectively. Between PID 8 and 27, CDV antigen was abundantly present in marrow cells, osteoclasts, and osteoblasts and less frequently in osteocytes. Immunopositive cells in both osseous tissues and bone marrow declined between PID 29 and PID 36 and were absent by PID 41. Chondrocytes of the growth plate were negative for viral antigen throughout the observation period. In bone, viral antigen was more frequently observed in bone cells of the primary spongiosa than in the secondary spongiosa. There was a strong correlation between occurrence of CDV antigen and osseous changes. Associated metaphyseal bone lesions were mild and most prominent between PID 8 and PID 32. Lesions consisted of necrosis of osteoclasts, which was associated with subsequent persistence of the primary spongiosa (growth retardation lattice). Atrophy and necrosis of osteoblasts and marrow cells were also noted. Infection of metaphyseal bone cells appears to be common in young dogs with experimental systemic distemper. Bone cell infection is preceded by infection of marrow cells, and infected bone cells may experience degeneration and necrosis. This subtle viral effect may result in defects in bone modeling in CDV-infected dogs.

Canine bone marrow cell cultures infected with canine distemper virus: an in vitro model of Paget's disease

We have previously shown that the canine paramyxovirus, canine distemper virus (CDV), is a possible aetiologic agent in Paget's disease of bone and in the canine bone disorder, metaphyseal osteopathy. More recently, we have examined the effects of CDV on the formation of multinucleated, tartrate resistant acid phosphatase positive, calcitonin receptor positive, osteoclast-like cells in cultures of canine bone marrow mononuclear cells, and shown that both in vitro and in vivo infection with CDV produced a dose dependent increase in the number and size of osteoclast-like cells. We have now extended these results to show that CDV infection induces interleukin-6 and c-Fos mRNA in these cells, similar to our recent findings in pagetic bone cells. These results further support the hypothesis that CDV might be involved in the aetiopathogenesis of Paget's disease and metaphyseal osteopathy and suggest that canine marrow culture systems will prove useful as an in vitro model to examine the disease processes in more detail.

Osteoclast function in Paget's disease and multiple myeloma

Paget's disease of bone and multiple myeloma are characterized by increased numbers of osteoclasts and markedly increased bone resorption at the sites of the disease. In Paget's disease the osteoclasts are abnormal morphologically and contain viral-like nuclear inclusions, but in multiple myeloma the osteoclasts are normal. The bone lesions in both Paget's disease and multiple myeloma appear to be due to local stimulation of osteoclast formation and bone resorption. In situ hybridization techniques, bone marrow cultures, and cytokine assays have been used to examine osteoclast function in Paget's disease and multiple myeloma. Interleukin-6 (IL-6) has been implicated as a potential mediator for the increased osteoclast activity in both diseases. In Paget's disease, IL-6 is produced by the osteoclasts, the osteoclasts express IL-6 receptors and IL-6 mRNA, and increased levels of IL-6 are present in the marrow plasma and serum of these patients. Similarly, increased levels of IL-6 have been detected in sera from some patients with multiple myeloma. Multiple myeloma cells do not produce IL-6 in vivo but marrow stromal cells or the osteoclasts may be the source of IL-6 in multiple myeloma. IL-6 is a growth factor for multiple myeloma cells, and treating patients with anti-IL-6 decreases the tumor burden in some patients. Thus, IL-6 may be an autocrine/paracrine factor in both Paget's disease and in multiple myeloma. Multiple myeloma cells also produce osteoclast activating factors (OAFs) that can stimulate osteoclast formation and activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Generation of multinucleated osteoclast-like cells from canine bone marrow: effects of canine distemper virus

Recent evidence has implicated canine distemper virus (CDV) as a possible aetiologic agent in Paget's disease of bone and the canine bone disorder, metaphyseal osteopathy. We have therefore examined the effects of CDV on the formation of multinucleated osteoclast-like cells in cultures of canine bone marrow mononuclear cells. Marrow cells from a distemper-infected dog and from five uninfected dogs were cultured in the presence of 1 alpha, 25-(OH)2 vitamin D3 and the number of tartrate resistant acid phosphatase positive multinucleated cells (MNCs) was determined. The presence of calcitonin (CT) receptors was confirmed by autoradiography with 125I-labeled human CT. Cultures from the distemper-infected dog contained a higher level of MNCs than those from the normal dogs. The in vitro addition of CDV to the cultures from all the dogs produced a dose-dependent increase in the number of MNCs, and an increase in size of these cells in the cultures from the infected dog. Cells infected with CDV were hyperresponsive to 1 alpha,25-(OH)2 vitamin D3. The presence of the virus in the relevant samples was confirmed using molecular techniques. In situ hybridization studies also revealed a significant increase in the level of infection following in vitro addition of the virus to the culture from the distemper-infected dog, suggesting that further infection had taken place. Resorption pits were formed on bone slices, although the number of pits was not significantly altered by viral infection.(ABSTRACT TRUNCATED AT 250 WORDS)

Frequency and characteristics of familial aggregation of Paget's disease of bone

The cause of Paget's disease of bone (PDB) is unknown. In an attempt to ascertain the proportion of familial cases and evaluate the influence of genetic factors on the occurrence of the disease, a study was undertaken based on 35 PDB patients from our Unit. Their families were investigated, with the participation of a total of 128 first-degree relatives. Fourteen (40%) of these 35 index cases had at least one other first-degree relative affected with PDB and were defined as "familial." The remaining 21 (60%) were considered "sporadic." The frequency of males in the familial cases (79%) was significantly higher than among the sporadics (29%; p < or = 0.01). Mean age at diagnosis (63.1 +/- 12.6 vs. 71.3 +/- 8.7; p < or = 0.02), proportion of polyostotic cases (85.7% vs. 52.4%, p < or = 0.05), and mean number of involved bones per patient (4.36 +/- 2.50 vs. 2.33 +/- 1.93, p < or = 0.01) differ significantly in the familial and sporadic groups. The disease appears to be transmitted via both paternal and maternal sides, and pedigree analysis suggested an autosomal dominant inheritance or multifactorial mechanism. Apart from green-and-blue eye color, which was clearly associated with familial grouping (OR 6.25, 95% CI 1.15-37.16, p < or = 0.01), crude analysis on several genetically based traits and environmental variables revealed no other significant differences between the groups. The adjusted odds ratio estimated for green-and-blue eye color was 2.92 (95% CI 0.38-22.74).(ABSTRACT TRUNCATED AT 250 WORDS)

Multiple osteomas in mice

Osteomas (dense compact neoplasms of mature bone tissue) are rare in nearly all strains and stocks of mice. Of 224 Him:OF1 mice maintained until natural death or until terminally ill, 116 (51.8%) had one or more osteomas. Osteomas had a predilection for the skull and the larger bones of the limbs. Plasma alkaline phosphatase concentrations were elevated significantly in osteoma-bearing mice (446 +/- 153 U/liter versus 206 +/- 65 U/liter in age-matched controls without osteomas). Only very large osteomas resulted in clinical signs, and longevity was not shortened. Histologic examination showed clearly separated dense bony tissue irregularly arranged and forming a mosaic pattern, with distinct cement lines and medullary spaces filled with fibroreticular connective tissue. Electron microscopic examination revealed virus-like structures in osteoblasts, osteocytes, and fibroblasts and in the place of remnants of necrotic cells.

Dogs, distemper and Paget's disease

The cause of Paget's disease is still unknown, despite many years of intensive study. During this time, evidence has sporadically emerged to suggest that the disease may result from a slow viral infection by one or more of the Paramyxoviruses. More recently, epidemiologic and molecular studies have suggested that the canine paramyxovirus, canine distemper virus, is the virus responsible for the disease. If true, then along with rabies, this would be a further example of a canine virus causing human disease. Studies in the natural host have now supported these findings. Further investigations have proposed that the bony abnormalities seen in Paget's disease are due to the effects of the virus on osteoclastic interleukin-6 and c-FOS production, possibly via the transcription factor NF-kappa B.