Osteolytic form of Paget's disease. Differential diagnosis and pathogenesis.

Of fourteen patients with Paget's disease for whom adequate roentgenograms and pathological material were available, six had lesions showing significant or predominant osteolysis. Based on a study of these six patients and a review of the literature, the following mechanisms were identified as causes of the so-called osteolytic type of the disease: (1) an "early" destructive Paget's lesion; (2) "advanced" Paget's disease with secondary degenerative changes; (3) "seeding" of an independent osteolytic lesion, particularly tumor in pre-existing Paget's disease; (4) sarcomatous transformation; and (5) immobilization after fracture. An osteolytic lesion in a patient without other bone disease may be due to Paget's disease, while an associated lytic lesion may be the result of a variety of conditions. Accurate pathological diagnosis is essential.