Fine structure of nuclei and cytoplasm of osteoclasts in Paget's disease of bone

Abstract

To investigate the fine structural features of nuclei and cytoplasm in osteoclasts from patients with Paget''s disease of the bone, 8 bone biopsies were examined. Unusual paracrystalline filamentous formations were found within the nuclei of actively resorbing and degenerating osteoclasts. These formations were made up of parallelly arranged filaments which usually clustered together regularly. The filaments were slightly argyrophilic and this helped to differentiate them from the surrounding nuclear matrix, even when they were not aggregated in clusters. Argyrophilic filaments were also found loosely aggregated inside the cytoplasm of osteoclasts. In 3 biopsies 2 additional and unusual cytoplasmic inclusions were found. The first consisted of irregularly branching, highly argyrophilic membranous strands which were located inside membrane-bound vacuoles. The second consisted of spindle-shaped structures enclosed by 2 membranes and containing 3 or more tubules. These results stand as further morphological evidence in favor of the view that a virus, possibly of the paramyxovirus class, has a pathogenic role in Paget''s disease of the bone.