Paget's disease of bone.

Paget's disease of bone is characterized by an anarchic bone remodelling, associated with morphological and functional abnormalities of osteoclasts. Its prevalence and incidence rates decreased gradually over the past two decades; the reason for this remains unclear. The aetiology of the disease is still obscure, the paramyxoviral theory being very controversial. Recent advances in understanding of the disease come from genetic studies, with the identification of specific mutations in the p62-sequestosome gene, which could be involved in pathogenetic mechanisms leading to increased osteoclast activity. The disease affects one or several bone pieces, leading to bone pain, deformities, characteristic imaging features, and increased markers of bone remodelling. The long-lasting disease activity leads to complications, including arthropathies, neurological compressions, fissures or fractures and, rarely, osteosarcomatous transformation of a pagetic lesion. Potent bisphosphonates have proven their efficacy in reducing symptoms and disease activity. They are currently used as the first-line treatment with the goal of normalizing bone remodelling and, hopefully, preventing late complications.