All the following are true of Paget disease Except

Paget disease is a disorder of unknown origin, which occurs in older people and involves either a single bone or several bones. It is not associated with systemic metabolic disturbances, and some pas of the skeleton are always spared. The bones show marked thickening, owing to excessive osteoblastic and reduced osteoclastic activity. Although only a few persons suffering from Paget disease develop sarcoma of bone, in adults the disease remains an impoant predisposing condition for this tumor in long bones. The skull and veebrae are viually never the sites of secondary osteogenic sarcomas. Ref: Maheshwari 6e pg 317.