[How to evaluate the activity of Paget's disease in clinical practice and which patients should be treated?].

In patients with Paget's disease, the alkaline phosphatase level (AP) is a measure of the phosphatase activity throughout the skeleton, i.e. the activity of normal bone tissue as well as that of Pagetic bone, in proportion to their respective volumes. This test therefore greatly under-estimates the activity of Pagetic bone in localized forms of the disease. To accurately evaluate the activity of Pagetic bone, the value of AP needs to be expressed in terms of the percentage of bone tissue affected by the disease. Two tables enable us to assess this percentage approximately. It is therefore possible to evaluate the activity of Pagetic bone on the basis of the tables presented by the authors. We can see that localized forms of Paget's disease may have an alkaline phosphatase activity of 2 000 or 3 000 I.U., while the AP levels in the blood are less than 200. So, in the presence of localized forms of the disease, we are unable to say that the disease is barely active on the basis of very low values for AP. It is important to treat localizations which have a "functional" risk for the future, especially when there localizations are highly active. The histopathological and scintigraphic data are compatible with areas of ery high activity. A similar rationale should be applied to the figures obtained for urinary hydroxyproline and the results of 45Ca kinetic studies.