[Pathogenesis of otosclerosis. "State of the art"]

Women suffer from otosclerosis 1.6 times more often than males. Histologically, otosclerotic foci can be found in temporal bones of females 1.9 times more often than in those of males. Characteristic topographic regions are the oval window, round window niche and promontory. Otosclerosis can also occur principally in any area of the enchondral/periosteal layer of the otic capsule. Evidence is presented that otosclerosis is an inflammatory tissue reaction associated with macrophages, T- and B-lymphocytes, HLA-DR positive cells and plasma cells. Dependent on the stage of the osteolytic bone disease present deposits of complement and immunoglobulins (IgG, IgA) can be found. These immunoglobulins have been identified as antibodies to measles virus proteins. Using the polymerase chain reaction we were successful in demonstrating RNA sequences of measles viruses in otosclerotic bone from footplates removed during stapes surgery. Since most of the otosclerotic lesions were in direct contact to the perilymphatic space, it may be expected that the endolymphatic sac--as the immune competent organ of the inner ear--specifically reacts to antigens delivered from the otosclerosis focus into the perilymph. Perilymph samples from patients were collected during stapes surgery and their antibody titers against measles were compared with that in corresponding blood serum. All samples revealed a significantly elevated-specific anti-measles IgG amount which was significantly higher than in the corresponding serum. In contrast, antibody titer in the perilymph against herpes simplex or cytomegalo viruses did not differ from that of the serum. These findings indicate that otosclerosis is a measles virus associated inflammatory osteolytic disease of the temporal bone. Since women suffer from severe measles virus infections more often than males, it can be hypothesized that females have a higher susceptibility of their cochleo-vestibular tissues to these infections (organotropism). In addition, estrogens are well-known stimulators of osteocytic activity and may play a dominant role during ossification of an otospongeotic bone lesion. This may explain the onset of a conductive hearing loss due to otosclerosis during pregnancy.