Prevalence of Paget’s disease of bone in Lancaster: time for an update

Rheumatology key message There is a striking decline in the overall prevalence of Paget’s disease of bone in Lancaster. Sir, between 1970 and 1977, a survey of Paget’s disease of bone (PDB) [1, 2] provided comprehensive data on the radiological prevalence of the disease in men and women >55 years of age in 31 British towns. Around 30 000 abdominal radiographs, undertaken for various reasons, were evaluated against set radiographic criteria [3, 4]. The results of this survey revealed 6.2 and 3.9% prevalence rates for men and women, respectively, and an overall prevalence of 5%. A remarkable variation in the prevalence was noted, with the highest rates in the Lancashire area and a sharp decline outside it. The highest prevalence was found in Lancaster, with an overall rate of 8.3% (male 6.5%, female 10%; male:female ratio 0.65). A second survey carried out between 1993 and 1995 [5] using similar sampling and radiographic methodology looked at the prevalence of the disease in 10 towns among those surveyed in the original study, including Lancaster. The abdominal radiographs of ∼10 000 patients were examined and the results showed a steep decline in prevalence rates, with an overall rate of 2% (male 2.5%, female 1.6%). The decline in prevalence was most marked in those centres with higher rates in the original study. Although Lancaster was still the highest in prevalence, the overall rate was less than half that previously reported (3.7%), with different gender-adjusted values (male 3.7%, female 3.8%; male:female ratio 0.97). As there have been no further studies in the Lancashire area since, we undertook a survey to update the prevalence of PDB in Lancaster 20 years later. Institutional ethical review was granted for this study by the Head of Research and Development, Clinical Director of Core Services and the Clinical Lead for Rheumatology. Using the same criteria for radiological diagnosis of PDB [3, 4], we retrospectively evaluated 1000 abdominal and pelvic CT scans undertaken for various reasons in patients ⩾55 years of age who resided in Lancaster. Each scan covered the whole pelvis, all lumbar vertebrae, sacrum, coccyx and upper femurs. Scans were analysed in the axial, sagittal and coronal formats using bone windowing. The results showed a higher male:female ratio (3) and a striking decline in the overall prevalence to 0.8% (male 1.2%, female 0.4%), in keeping with the previously seen declining rates in PDB. We chose to use CT scans rather than abdominal radiographs, as used in the previous studies, because clinically CT has superseded abdominal radiographs in most circumstances. Therefore there was a risk that using plain abdominal radiographs would have resulted in skewing the population included to a small number of conditions. CT is more sensitive than abdominal radiographs in detecting early and subtle bone changes related to PDB. With a higher sensitivity, the declining rates seen in our study are made even more valid than if plain radiographs been used for assessment. The epidemiological findings of our study in tandem with the previously published literature have implications on the current understanding of the causation of PDB. Previous studies tried to explain the geographic variation in different parts of Britain. The latitude and industrialized nature of the Lancashire area do not seem to be playing a part [1], neither does the nature of the drinking water [2]. Studies also tried to explain the decline in disease prevalence. Little is known about the pathogenesis of PDB. Genetic predisposition plays a role; this is supported by the fact that PDB is transmitted vertically in affected families [6] and the higher prevalence of the disease in areas of the world colonized by people of British descent who inherited a predisposition to develop the disease, like New Zealand [4]. Environmental triggers, namely chronic paramyxovirus infection, are also postulated [7]. However, this hypothesis has been debated in the literature and many studies fail to support it [8]. Other environmental factors have been implicated in disease aetiology and possibly the changing trend of the disease, including childhood diet, physical activity, oral bacteria, viruses, zoonotic infections and occupational exposure [4]. Overall, the most likely pathogenesis is a combination of environmental factors affecting genetically predisposed individuals, which changes disease prevalence in different areas and within the same area over time. Funding: No specific funding was received from any bodies in the public, commercial or not-for-profit sectors to carry out the work described in this article. Disclosure statement: The authors declare no conflicts of interest.