Dynamic bone studies of the labyrinthine capsule in relation to otosclerosis

The pathological perilabyrinthine bone remodelling of otosclerosis is associated with a genetic predisposition and triggered by mechanisms so far unknown. A proposed viral aetiology of otosclerosis originates from a similar concept of Paget's disease. However, at present, it is not clear why a virus should cause otosclerosis, confined to the bony otic capsule with no effects on the general skeleton in some patients, and systemic Paget's disease with only occasional involvement of the bony otic capsule in others. Moreover, the extent and distribution of pathological bone remodelling is different in Paget's disease of the temporal bone and in otosclerosis. Bone resorption and consequently bone remodelling which turns over the general skeleton at a rate of 10% per year is normally highly restricted in perilabyrinthine bone to a minimum of 0.13% per year except in otosclerosis, and systemic remodelling rates are normal even in otosclerotic patients. This suggests the existence of a local inner ear mechanism in control of capsular remodelling activity, which is either overruled, bypassed or most likely defective in otosclerosis, no matter what may have triggered the disease process. We present experimental data related to this mechanism, which may offer a truly local pathogenetic factor in otosclerosis.