Snapshot A 60-year-old man presents to his primary care physician with hip pain and hearing loss. He denies any trauma to the hip or any recent changes in his medications. He also notes his hat fits tighter than before. Physical examination is unremarkable. Laboratory testing is significant for an elevated alkaline phosphatase level in the setting of normal serum calcium, phosphate, and parathyroid hormone. Introduction Clinical definition a progressive metabolic bone disorder of abnormal bone remodeling excessive bone resorption and formation is present Epidemiology incidence second most common metabolic bone disorder (osteoporosis is first) age > 55 years of age Etiology Unknown Pathogenesis increased multinucleated osteoclastic and osteoblastic activity leads to a high bone remodeling rate resulting in abnormal bone architecture (lytic and blastic lesions) Presentation Symptoms usually asymptomatic bone and/or joint pain bone deformity bowing deformity hearing loss with skull involvement that leads to narrowing of the auditory foramen Physical exam typically unremarkable Imaging Radiography indication to identify osteolytic, osteoblastic, and sclerotic bone changes Bone scintigraphy indication to determine the extent of Paget disease of bone and to assess for other sites of involvement Studies Labs normal serum phosphate, calcium, and parathyroid hormone elevated alkaline phosphatase Histology mosaic pattern of lamellar bone with prominent cement lines Differential Laboratory Abnormalities in Select Bone DisordersEtiologySerum PhosphateSerum CalciumSerum Alkaline PhosphataseParathyroid HormoneOsteomalacia/ricketsDecreasedDecreasedIncreasedIncreasedOsteoporosisNormalNormalNormalNormalOsteopetrosisNormalNormal or decreasedNormalNormalPaget disease of the boneNormalNormalIncreasedNormalOsteitis fibrosa cysticaPrimaryhyperparathyroidism• decreasedSecondaryhyperparathyroidism• increasedPrimaryhyperparathyroidism• increasedSecondaryhyperparathyroidism• decreasedPrimary and secondary hyperparathyroidism• increasedPrimary and secondary hyperparathyroidism• increasedHypervitaminosis DIncreasedIncreasedNormalDecreased Treatment Medical bisphosphonates indication first-line treatment for Paget disease of bone Surgical orthopedic surgery (e.g., joint/knee arthroplasty) indication to manage symptomatic complications of Paget disease of bone (e.g., osteoarthritis, pathologic and pseudofractures, and spinal stenosis) Complications Neurologic nerve root compression hearing loss spinal stenosis Orthopedic pathologic fractures secondary osteoarthritis Oncologic osteosarcoma Cardiovascular high-output heart failure abnormal bone deposition leads to increased bony vascularization, which decreases systemic vascular resistance (afterload), leading to high-output heart failure Prognosis Expansion of untreated Paget lesions