Symptomatic and scintigraphic improvement after intravenous pamidronate treatment of Paget's disease of bone in patients with normal serum alkaline phosphatase levels

To describe three patients with symptomatic Paget's disease of bone who presented with normal levels of serum alkaline phosphatase. We present three cases of Paget's disease of bone and chronicle the laboratory, scintigraphic, and clinical findings relative to treatment with intravenously administered pamidronate. Although measurement of serum total alkaline phosphatase usually provides a general indication of bone turnover in Paget's disease, about 15% of patients present with normal serum alkaline phosphatase levels. Nonetheless, these patients may have active Paget's disease when assessed with bone scintigraphy or urinary markers of bone resorption. All three study patients had xray findings characteristic of Paget's disease of bone, increased uptake of radiotracer material on bone scans, and elevated levels of urinary markers of bone resorption but normal alkaline phosphatase levels. They were treated with intravenously administered pamidronate, 60 mg once weekly for 2 to 3 consecutive weeks. After treatment, the serum alkaline phosphatase level decreased by 19 to 36%, markers of bone resorption normalized, bone scans showed improvement, and bone pain resolved. Pagetic activity in bone and related clinical manifestations may be present in the setting of a normal serum alkaline phosphatase level. Appropriate therapy should not be withheld because of the normal alkaline phosphatase.