Initiating antiresorptive therapy in this patient with symptomatic Paget disease of bone is the most appropriate next step in management. Paget disease of bone is characterized by focal areas of accelerated bone remodeling that ultimately causes overgrowth of bone at one or more sites that may impair the integrity of affected bone. Areas commonly affected include the skull, spine, pelvis, and long bones of the lower extremities, such as in this patient who has thickened cortical bone and coarsening of the trabecular bone of the femur. The main indications for antiresorptive therapy in most patients include pain caused by increased bone metabolic activity (as in this patient) and hypercalcemia due to multiple affected sites. The most commonly used treatment agents are nitrogen-containing bisphosphonates (alendronate, pamidronate, risedronate, and zoledronic acid); these are the newer bisphosphonates and have been the most extensively studied for treatment of Paget disease of bone. Bisphosphonates stabilize bone turnover by suppressing bone resorption and new bone formation with a resulting reduction in serum alkaline phosphatase levels. There is no evidence that antiresorptive therapy is beneficial in asymptomatic patients.

Bone biopsy is rarely needed to establish the diagnosis of Paget disease of bone when there are characteristic radiographic findings of bone turnover (concurrent osteolytic and osteoblastic changes) and consistent laboratory studies (such as elevated serum alkaline phosphatase levels). Bone biopsy may be useful in certain situations in which bone lesions are primarily osteoblastic (suggesting possible metastatic disease) or osteolytic (possibly indicating multiple myeloma), neither of which are present in this patient.

The bone lesions of multiple myeloma are primarily osteolytic, in which case further evaluation for that diagnosis with a serum and urine protein electrophoresis would be appropriate. However, this patient's radiographic findings are not consistent with a diagnosis of multiple myeloma, and further evaluation for this disorder would therefore not be indicated.

Most patients with Paget disease of bone are asymptomatic and are identified only by elevated serum alkaline phosphatase levels detected on laboratory studies obtained for other reasons. In many patients with mild disease, clinical observation without initiation of therapy is appropriate. However, in this patient with symptomatic disease in a critical weight-bearing skeletal area, clinical observation without treatment would not be appropriate.