gms | German Medical Science

Introduction: The role of Bone Morphogenetic Proteine (BMP) in various tissue growth and repair mechanisms is an ongoing topic in literature. BMP 2, 4 and 7 are known to be the most important BMP in bone formation and repair in humans. Their role in otosclerotic bone transformation has not been analysed previously.

Method: The posterior parts of the stapedial footplates, collected within the scope of 29 partial stapedectomies in patients with otosclerosis were histologically analysed for otosclerotic lesions after hematoxylin staining. Immunohistochemical analysis was performed using polyclonal IgG antibodies for BMP 2, 4 and 7, as well as biotinylated secondary antibodies, avidin-biotin-peroxidase complex reaction and alkaline phosphatase staining. Attic bone fragments served as control. All specimens were independently rewied by each of the three authors.

Results: 14 specimens contained otospongiotic, 8 sclerotic lesions, thus in total 22/29 cases (76%) of histological otosclerosis. 20 of these 22 specimens were positive for BMP 2, 4 and 7, clearly evident by means of strong immunochemical staining in the nuclei of the numerous osteoblasts and osteoclasts. In one case each only BMP 2 respectivly BMP 2 and 4 have been positive.

Conclusion: Despite the fact that literature reflects a clear predilection site for otosclerosis in the anterior footplate and the fissula ante fenestram in our series the posterior part contained otosclerosis in 76%. This is due to a selection bias, as we only analysed otosclerosis with clinical manifestation instead of unselected series of temporal bones like in most other studies. BMP 2, 4 and 7 seem to play a role in otosclerotic lesions. Further investigations - especially for the phosphorylated Smad proteins within the BMP dependent mediator cascade - will be necessary. This will also verify if there is any therapeutical benefit.