Paget's disease of bone in New Zealand: continued decline in disease severity

We have reported previously that severe Paget's disease of bone had become less common at our center between 1973 and 1993. Data from several countries support the view that there are important secular trends in the prevalence and severity of Paget's disease. In this paper we describe recent trends in the demography of newly referred patients with Paget's disease to determine if the secular trend toward milder disease has continued. A database of all newly referred patients (n = 1487) with Paget's disease (1973 to 2002 inclusive, 30 years) was examined. Of these, 832 subjects (56%) had scintiscans. Plasma total alkaline phosphatase (total ALP) activity, disease extent on scintiscan, and a derived index of average ALP activity of pagetic bone were used as indices of severity. The number of new referrals with Paget's disease declined sharply from 1994 onward and is currently at half the rate seen 20 years earlier, while the mean age at presentation has progressively increased by 4 years per decade (P < 0.0001). Total ALP at diagnosis, disease extent on scintiscan, and the number of bones involved were all negatively correlated with both date of birth (P < 0.0001) and year of presentation (P < 0.0001), indicating that more recently born and presenting subjects had substantially less severe bone disease. The average activity of pagetic bone was only weakly correlated with year of presentation, but not with year of birth or age at presentation. Although there are a number of potential biases, these data are consistent with a continued secular trend to presentation in older subjects with less extensive skeletal involvement, and a declining prevalence of Paget's disease.