Paget’s Disease of the Bone is a disorder where resorption of bone by hyperactive osteoclasts outpaces the ability of osteoblasts to keep up (ie, laying down strong organized bone).
This results in focal lytic lesions affecting one or many bones, as well as areas of proliferation of soft, disorganized bone.
This xray of the pelvis shows earlier signs of Paget's disease: thickening of the femoral neck and diffuse sclerosis of bone.
This xray shows more advance deformity:
The disease runs in families and though the etiology is not entirely clear, it is commonly thought to have both a genetic and a viral component. It is a disease of older patients; those younger than 40 years are rarely affected, with incidence increasing thereafter with age. It is also more common among people of European descent and has a slight predilection for males over females.
Aching bone pain is the most common presenting symptom, but patients are often asymptomatic early in disease, and frequently picked up by incidental radiographic findings or due to blood work that reveals an elevated alkaline phosphatase.
A bone scan will be "hot" because of the increased remodeling activity
Mr. Smith is right to be happy that cancer hasn’t been found. (Paget’s Disease of the Nipple, a rare form of breast cancer, is unrelated except by name.) Nonetheless, Paget’s is associated with increased risk of bone malignancy, affecting about 1% of people with disease and with osteosarcomas of the pelvis, femur, humerus and skull seen most frequently.
Additionally, he should not be dancing for joy (or anything else for that matter!) too aggressively because in addition to accelerated OA, another complication of Paget’s is increased fracture risk.
Fortunately for him, remission (understood as normalizing of x-ray findings, serum alk phos and relief of pain–not "cure") can be achieved in more than 90% of patients via IV bisphosphonate therapy. He’ll need good follow up and continued monitoring for recurrence or malignancy going forward.