Diagnostic suspicion arises if laboratory and imaging methods reveal elevated serum alkaline phosphatase levels and bone changes. However, in about 10 % of patients, concentration of alkaline phosphatase may be within the reference range. In such case certain markers of bone resorption may be helpful, such as hydroxyproline, pyridinolines, N- or C-telopeptides, P1NP and bone alkaline phosphatase. There is good correlation of bone markers with disease activity, as seen by bone scintigraphy. Calcium and phosphorus levels are commonly within reference ranges, but 20 % of patients may have elevated parathyroid hormone levels, and sometimes elevated uric acid levels.

Due to their typical nature, changes are readily identifiable by imaging techniques. Paget’s disease has several typical features, such as cotton-wool appearance of skull bone, due to enlarged osteolytic region and bone hypertrophy (Fig. 33.1b). Computed tomography and nuclear magnetic resonance imaging are used to assess nerve compression and ill-defined stress fractures and to examine tumour transformation (Fig. 33.1c). Bone scintigraphy is helpful in detecting the scope of the disease (Fig. 33.2). In some patients, scintigraphic changes may appear prior to radiological changes.