A 77-year-old woman presented with pain in the right elbow of several years duration. There was no history of trauma, immunocompromise, or known malignancy. Blood chemistry tests revealed an alkaline phosphatase level of 93 U/L (1.6 μkat/L) (30-120 U/L [0.5-2.0 μkat/L]), a sodium level of 139 mmol/L (135-147 mmol/L), a potassium level of 4.4 mmol/L (3.4-5.0 mmol/L), a calcium level of 2.38 mmol/L (2.2-2.55 mmol/L), a phosphate level of 1.81 mmol/L (0.85-1.5 mmol/L), a C-reactive protein level of less than 5 mg/L (47.6 nmol/L), and an erythrocyte sedimentation rate of 41 mm/h (0-15 mm/h). Hematologic findings were normal. Imaging included plain film radiography, computed tomography (CT), and magnetic resonance (MR) imaging of the right humerus. Bone biopsies were obtained 3 months and 4 years after initial presentation.