Current aspects of etiology, diagnosis and therapy of otosclerosis

Otosclerosis is a circumscribed disease of the enchondral bone of the otic capsule. It is characterized by alternating phases of bone resorption followed by replacement with dense sclerotic bone. The first identification of this disease was made by Valsalva in 1704 in a description of the bony obliteration of the oval window in a patient with an aquired deafness [64]. The term otosclerosis was introduced by Anton von Tröltsch in 1872, remarkably no difference was made between otosclerosis and tympanosclerosis [66]. Politzer introduced the term otosclerosis as a separate entity in 1894 as the final stage of the disease with sclerotic plaques in the otic capsule [44]. Otosclerosis is a disease with a pathologic remodeling of the bone at a place where remodeling is uncommon in adults. Up to present knowledge usually there is no activity of osteoblasts and osteoclasts in the healthy otic capsule. However in otosclerosis there is pathologic bone resorption of the enchondral bone by osteoclasts in the first stage of the disease (otospongiosis) followed by bony formation made by osteoblasts (otosclerosis in the actual sense). Mosty otosclerotic plaques are found in the anterior part of the oval window (fissula ante fenestram). E. g. Schuknecht and Barber showed a fixation the footplate in the anterior part in 96% of their patients [50]. The term “obliterative otosclerosis” is used in cases with a complete ossification of the oval window accompanied by a severe conductive hearing loss. Otosclerosis is a disease limited to the temporal bone and never found in any other bone of humans [68]. The “malignant otosclerosis” is a term of the otosclerotic remodeling which is not restricted only to the oval and round window but the complete temporal bone including the inner ear which can be followed by a progressive combined severe hearing loss up to nearly complete deafness [52]. The etiology of otosclerosis is not definitely clarified up to now. Currently different hypotheses are discussed: