Decline in clinical severity of Paget's disease of bone: Comparison between a contemporary cohort and a historical cohort.

Background: European and Australian studies have reported a decrease in the prevalence, incidence and clinical severity of Paget's disease of bone (PDB). There are no studies on the current clinical characteristics of PDB in Quebec, Canada.

Aims: The purpose of this study was to describe the characteristics of unrelated patients with PDB diagnosed after the year 2000 in our region and to compare them to a historical cohort diagnosed before 2000.

Methods: In this retrospective descriptive cohort study, socio-demographic data and clinical characteristics for the contemporary cohort were collected from electronic medical records of patients with PDB followed at our university hospital. For the historical cohort, the same data were collected from the research files of PDB participants in our research program. Inclusion criteria were: age > 18 years, having PDB diagnosed by a rheumatologist, and being followed in our hospital. Exclusion criteria were: having a relative with PDB participating in this study. Variables were reported as mean, standard deviation, frequency and percentage. Chi-square tests were used to compare categorical variables. Continuous values were compared with Wilcoxon-Mann-Whitney tests. Unadjusted p-values and adjusted p-values with the Bonferroni correction method were calculated. A p-value <0.05 was considered statistically significant.

Results: Among the 195 patients with PDB in the contemporary cohort, 53.3 % were men, 60.5 % had monostotic involvement, 14.2 % were symptomatic at diagnosis. In comparison to the historical cohort of 173 patients, patients in the contemporary cohort were older at diagnosis (68.7  10.7 vs. 58.5  10.1; p < 0.0001) and had less family history of PDB (13.8 % vs. 33.6 %; p = 0.0024). They also had lower total alkaline phosphatase levels at diagnosis (118.0 (85.0-184.0)) vs. 184.0 (115.0-312.0)); p = 0.0006), a lower pagetic bone number (1.0 (1.0-3.0) vs. 2.0 (1.0-5.0); p < 0.0001), lower pagetic bone fractures (6.7 % vs. 36.7 %; p = 0.0078) and lower bone deformities (13.0 % vs. 54.0 %; p < 0.0001). There was no significant difference for pagetic bone pain (52.0 % vs. 52.6 %; p = 1.0000), percentage of patients who had orthopedic surgery related to PDB complications (8.8 % vs. 28.6 %; p = 1.0000), secondary osteoarthritis (43.0 % vs. 51.6 %; p = 1.0000), and hearing impairment (51.9 % vs. 61.1 %; p = 0.1000).

Conclusion: The contemporary cohort is characterized by an older age at diagnosis, a majority of monostotic disease and fewer complications of PDB. This decline in clinical severity of PDB in Quebec is consistent with studies reported in other countries.