Otopathology in Osteogenesis Imperfecta
BACKGROUND: Osteogenesis Imperfecta (OI) is a genetic disorder of connective tissue matrix. OI is caused by mutations that affect type I collagen. The hearing loss in OI is characterized by onset in early adulthood and can be conductive, sensorineural, or mixed. OBJECTIVES: To describe the temporal bone histopathology in 9 individuals with OI. MATERIALS AND METHODS: Four adult, 1 pediatric, and 4 infant specimens were identified. Temporal bones were removed at autopsy and studied using light microscopy. RESULTS: All adults and 1 pediatric specimen showed otosclerotic lesions. The findings included examples of clinical, histologic, and cochlear otosclerosis. The temporal bones of infants showed delayed ossification of the endochondral layer of bone and of the ossicles. There were no infant specimens with otosclerotic lesions. CONCLUSION: Hearing loss in OI may be the result of clinical or cochlear otosclerosis. Fracture or atrophy of the ossicles may also be present in OI. A third unidentified mechanism of hearing loss may lead to cochlear degeneration. The described findings of otosclerotic lesions have implications for the observed heterogeneity of hearing loss patterns and for the surgical management of hearing loss in OI.
Available from: Tamara Alliston
- "The importance of this crosstalk is evident in bone syndromes where these pathways are disrupted. For example, otosclerosis and osteogenesis imperfecta tarda are characterized by sensorineural, conductive, and mixed forms of hearing loss –. "
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ABSTRACT: Normal hearing requires exquisite cooperation between bony and sensorineural structures within the cochlea. For example, the inner ear secretes proteins such as osteoprotegrin (OPG) that can prevent cochlear bone remodeling. Accordingly, diseases that affect bone regulation can also result in hearing loss. Patients with fibrous dysplasia develop trabecular bone overgrowth resulting in hearing loss if the lesions affect the temporal bones. Unfortunately, the mechanisms responsible for this hearing loss, which could be sensorineural and/or conductive, remain unclear. In this study, we used a unique transgenic mouse model of increased Gs G-protein coupled receptor (GPCR) signaling induced by expression of an engineered receptor, Rs1, in osteoblastic cells. These ColI(2.3)+/Rs1+ mice showed dramatic bone lesions that histologically and radiologically resembled fibrous dysplasia. We found that ColI(2.3)+/Rs1+ mice showed progressive and severe conductive hearing loss. Ossicular chain impingement increased with the size and number of dysplastic lesions. While sensorineural structures were unaffected, ColI(2.3)+/Rs1+ cochleae had abnormally high osteoclast activity, together with elevated tartrate resistant acid phosphatase (TRAP) activity and receptor activator of nuclear factor kappa-B ligand (Rankl) mRNA expression. ColI(2.3)+/Rs1+ cochleae also showed decreased expression of Sclerostin (Sost), an antagonist of the Wnt signaling pathway that normally increases bone formation. The osteocyte canalicular networks of ColI(2.3)+/Rs1+ cochleae were disrupted and showed abnormal osteocyte morphology. The osteocytes in the ColI(2.3)+/Rs1+ cochleae showed increased expression of matrix metalloproteinase 13 (MMP-13) and TRAP, both of which can support osteocyte-mediated peri-lacunar remodeling. Thus, while the ossicular chain impingement is sufficient to account for the progressive hearing loss in fibrous dysplasia, the deregulation of bone remodeling extends to the cochlea as well. Our findings suggest that factors regulating bone remodeling, including peri-lacunar remodeling by osteocytes, may be useful targets for treating the bony overgrowths and hearing changes of fibrous dysplasia and other bony pathologies.
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ABSTRACT: Bilateral hearing loss in a 44-year-old mother and her 17-year-old daughter was thought to be related to osteogenesis imperfecta (OI), although the other typical clinical signs and symptoms were scarce. Both showed a normal stature and no bone deformities. The mother has been followed up for 7 years as a case of sensorineural hearing loss, with one episode of acute deterioration in the lower frequencies about one year ago. She gave a history of suffering from bone fractures four times. The daughter showed bilateral mixed hearing loss and a blue sclera, but no history of bone fractures. CT images of the daughter showed extensive decalcified foci, suggestive of otosclerotic changes, in the otic capsule, however, no such changes were confirmed in the mother’s CT.In diagnosing the cause of sensorineural hearing loss, careful checkup of the family and past history and physical signs of OI, such as bone deformities and blue sclera, and CT should be considered. We should be aware that sensorineural hearing disorders in cases of OI may occur in the absence of the characteristic physical features.
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