Enchondral cartilage rests collagen-induced autoimmunity: a possible pathogenetic mechanism of otosclerosis

Immunohistochemical analysis of Otic Capsule Osteogenesis in the Palmerston North Autoimmune Mouse

Autoimmunity and the immune complex disease associated with it have been hypothesized to be the cause of several idiopathic diseases of the inner ear—including the new bone formation associated with otic capsule osteogenesis and otosclerosis. The Palmerston North (PN) autoimmune mouse strain, which exhibits both spontaneous systemic autoimmune disease and otic capsule bone formation, has been proposed as a model relating these two disease processes. To investigate the potential role of immunopathologic processes in PN otic capsule lesion formation, inner ears from PN mice were immunostained for the presence of IgG and complement (C3), two immunologic markers involved in the development of the vascular and perivascular changes associated with immune complex deposition. Both systemic autoimmune disease and otic capsule bony lesions were confirmed in all animals. However, immunohistochemical analyses did not establish a direct relationship between the two conditions as complement was absent in all lesions and IgG stained positive in only one instance. These results suggest that immune complex deposition is not directly involved in the otic capsule lesions of the PN mouse, and alternate mechanisms relating autoimmune disease and otic capsule osteogenesis must be explored.

The hypodense focus in the petrous apex: a potential pitfall on multidetector CT imaging of the temporal bone

BACKGROUND AND PURPOSE

Hypoattenuated foci in the otic capsule are routinely identified on multidetector CT (MDCT), particularly in pediatric patients. We aimed to describe and characterize the hypoattenuated focus in the anterior otic capsule.

MATERIALS AND METHODS

We first reviewed histologic sections of the temporal bone from 8-month-old fetuses to determine the nature of the hypoattenuated focus in the anterior otic capsule. A cadaver collection of skull bases from fetuses and neonates (n = 19), infants (n = 24), and young children (n = 23) were then studied with MDCT to determine the developmental evolution of this hypoattenuated focus in relation to the petrous apex. We specifically looked for the hypoattenuated focus in the anterior otic capsule, the development of the petrous apex, and the presence of other hypoattenuated foci in the fissula ante fenestram and middle otic layer.

RESULTS

The hypoattenuated focus in the anterior otic capsule corresponded histologically to a cancellous bone trabecula emanating from the middle otic layer and directed toward the petro-occipital fissure. At this level it was covered with a cartilaginous cap. The hypoattenuated focus was observed in all of the fetuses and in all of the postnatal subjects younger than 4 months of age and was always associated with hypoattenuated foci of the middle otic layer and the fissula ante fenestram. This hypoattenuated focus became less obvious as the petrous apex developed.

CONCLUSION

The hypoattenuated focus in the anterior otic capsule should be recognized as a normal variant in pediatrics. It could represent a relic from the development of the petrous apex.

Activated Osteoclasts with CD51/61 Expression in Otosclerosis

HYPOTHESIS

Stapes ankylosis is supposed to be a disease with variable histopathology caused by otosclerosis or pseudo-otosclerosis. Persistent measles virus infection of the otic capsule could induce reactivation of quiescent embryonic osteoclasts in otosclerosis.

BACKGROUND

Presence of measles virus RNA was demonstrated in the footplates of otosclerotic patients by reverse-transcription polymerase chain reaction (RT-PCR). Histology of active otosclerosis is featured by the presence of numerous osteoclasts with unknown phenotype.

METHODS

Nucleic acid was extracted from stapes footplates of clinically otosclerotic patients (n = 261). Genomic RNA of measles virus was amplified by RT-PCR. Amplification results were correlated to postoperative histologic and CD51/61 specific immunohistologic findings. A parallel alcalic phosphatase activity assessment was performed to evaluate the metabolic activity of osteoclasts in each section.

RESULTS

Among 261 stapes fixation cases, 175 otosclerotic stapes contained measles virus RNA. Histology for virus negative stapes (n = 86) represented nonotosclerotic, degenerative disorders. Histologically confirmed otosclerosis was featured by the presence of osteoclasts with renewed, embryonic phenotype. In otosclerosis, alcalic phosphatase activity was significantly higher compared with nonotosclerotic stapes ankylosis (P < .001).

CONCLUSION

The presence of CD51/61 positive osteoclasts in otosclerotic bone containing viral sequences provides the basis for an inflammatory bone remodeling disorder. Otosclerosis is a disease caused by persistent measles virus infection and reactivation of resting embryonic osteoclasts in the otic capsule.

Monogenic nonsyndromic otosclerosis: audiological and linkage analysis in a large Greek pedigree

OBJECTIVE

The aim of our study was to characterize the hearing impairment in a large multigenerational Greek family with autosomal dominant nonsyndromic otosclerosis and to perform genetic linkage analysis to known otosclerosis loci and collagen genes. In addition, we looked for mutations in the NOG gene to rule out congenital stapes ankylosis syndrome.

METHODS

Audiological analysis of the affected persons was based on multiple linear regression (MLR) analysis and construction of age-related typical audiograms (ARTA). Genotyping of microsatellite DNA polymorphisms for known otosclerosis (OTSC) loci or collagen genes and linkage analysis using the MLINK computer program were performed. The coding region of the NOG gene was screened for mutations by direct DNA sequencing.

RESULTS

The hearing loss in this family appears in childhood as conductive, but soon becomes mixed. Because the additional sensorineural component is progressive, this finally has lead to a pure sensorineural hearing loss in some family members, as the conductive component is masked. Audiological analysis showed an age-independent conductive component and a progressive frequency-specific sensorineural component. Linkage analysis excluded linkage to the four known otosclerosis loci (OTSC1, OTSC2, OTSC3, and OTSC5), as well as to the COL1A1 and COL1A2 genes. Mutation analysis of the coding region of the NOG gene did not reveal any disease causing mutation.

CONCLUSIONS

This study represents the first description of a detailed audiological analysis in a large pedigree segregating otosclerosis as a monogenic autosomal dominant trait. Exclusion of the four known otosclerosis loci in this family shows that monogenic otosclerosis is a genetically heterogeneous disease involving at least five different genes. A mutation in the NOG gene is not the underlying molecular mechanism of the early onset otosclerosis segregating in this family.

Increased Activity of the Diastrophic Dysplasia Sulfate Transporter in Otosclerosis and Its Inhibition by Sodium Fluoride

HYPOTHESIS

This study investigates the function of the diastrophic dysplasia sulfate transporter (DTDST) in otosclerotic bone and the effect on it of sodium fluoride (NaF).

BACKGROUND

Otosclerosis is a localized bone dystrophy with increased bone turnover. DTDST is implicated in the regulation of the bone turnover.

MATERIALS AND METHODS

Primary cultures of cells were obtained from the stapes and external auditory canal (EAC) of 26 patients with otosclerosis and from nine control patients. Sulfate uptake was quantified under basal conditions and with NaF. The NaF signaling pathways were investigated using forskolin and verapamil.

RESULTS

The relative initial rates of sulfate uptake and the apparent Vmax values were: otosclerotic stapes > EAC > control stapes = control EAC. The sulfate uptake by the otosclerotic stapes was correlated with the loss of sensorineural hearing. The amounts of DTDST mRNA (RNase protection assay) in the four subgroups did not differ. NaF (10(-6)M, 1 hr) inhibited sulfate uptake by the otosclerotic stapes and EAC cells but not by control samples.

CONCLUSION

The authors believe that whether the increased DTDST activity is a cause or an effect of otosclerosis, it appears to be a specific target for NaF treatment.

[Possible benefits of calcitonin in the treatment of otosclerosis]

This study shows the results obtained after treatment with intranasal calcitonin in 23 patients (36 ears) suffering from otosclerosis. 19.4% showed a hearing improvement upper of 10 dB. The gain was 32 dB in air conduction thresholds and 23 dB. In bone conduction. Tinnitus disappeared in 25% of cases suffering from tinnitus. Calcitonin tolerance was good, 8.7% of patients reported migraine. Authors recommended additional studies in order to evaluate the efficacy of this drug in the treatment of otosclerosis.

Antimeasles immunoglobulin G in sera of patients with otosclerosis is lower than that in healthy people

BACKGROUND

There is some evidence for an inflammatory process as a driving force in otosclerosis. Two popular hypotheses for the induction of this chronic inflammation have been proposed: an autoimmune phenomenon induced by an otic capsule specific antigen and measles virus infection.

METHODS

Antibodies against measles virus hemagglutinin, polymerase, nucleocapsid, and matrix proteins were evaluated in sera from otosclerotic patients and in sera from healthy age-and sex-matched controls by use of the Western blot analyses.

RESULTS

Significant differences were not detected between healthy men and women or between otosclerotic men and women. There were significantly stronger reactions against all viral proteins in the group of healthy women as compared with otosclerotic women despite a high standard deviation. The group of healthy male blood donors demonstrated significantly stronger reactions against polymerase and nucleocapsid proteins. Healthy blood donors again demonstrated stronger reaction compared with respective otosclerotic patients in a separate reaction for viral matrix protein.

CONCLUSION

Our observation is consistent with viral participation in otosclerotic pathogenesis, but it is difficult to say if the diminished antimeasles humoral response is a consequence or the cause for a local measles infection. In light of the present data, we can discuss autoantibodies in otosclerosis as a sign of autoimmunity triggered by measles virus.

Altered immunoregulations in otosclerosis: presence of autoantibodies in otosclerotic sera samples

A current concept of the etiopathogenesis of otosclerosis is an immune response. The purpose of this study was to determine if autoantibodies were present in sera samples from patients with known otosclerosis. Organ non-specific total antinuclear antibodies (tANA) were determined in 98 sera samples by the immunofluorescent method in 47.9% of otosclerotic patients versus 5% in controls. The most frequent specific antinuclear antibody was antibody to native deoxyribonucleinic acid and antibody to ribonucleoprotein. Tissue-specific antibodies to native-collagen type II molecule (ACA II) were determined by counter-immunoelectrophoresis in the same sera samples and were detected in 54% versus none in healthy sera. There was no correlation between the presence of these two autoantibodies. In patients with tANA present, a statistically significant depletion of cochlear function was noted. The presence of ACA II showed no connection with hearing loss. The present study showed some alteration in immunoregulatory markers in otosclerotic patients and the possibility that ANA may play a role in the pathogenesis of otosclerosis-induced perceptive deafness.

Composition of the otosclerotic stapes: electron microprobe analyses

For the first time, otosclerotic stapes have been distinguished from unafflicted controls at a high level of significance by using a spectrum of elements measured by energy-dispersive spectrometer-electron probe microanalyses (EDS/EPMA). Discriminant analyses of the maximum concentration of 13 elements measured at several sites within each of 32 stapes differentiated otosclerotic from unafflicted individuals well above the 95% confidence level. Eight of the 9 control (unafflicted) and 21 of the 23 afflicted stapes were correctly classified. In descending order of contribution to the discriminant function, the elements are Zn > Cr > K > Ca > Si > Mn > Na > Al > Mg > P > Fe > S > Ti. Zinc and chromium account for much of the difference, but discriminant analyses excluding them still distinguish the two groups at the 95% confidence level. These results are consistent with previous reports of high levels of alkaline phosphatase, a zinc-containing enzyme, in afflicted stapes. But the broad spectrum of elements capable of distinguishing otosclerotic stapes warrants study of additional zinc-containing and other metal-containing or metal-activated moieties.

Inner ear basic fibroblast growth factor in CBA/J, C3H/HeJ, and autoimmune Palmerston north mice

Basic fibroblast growth factor (bFGF) has a mitogenic effect on fibroblasts and osteoblasts for matrix proliferation and on endothelial cells for neovascularization. Because otic capsule osteogenesis in autoimmune disease subjects often involves abnormal matrix and vascular changes, bFGF may serve as a potential mediator for such bone disorders. To investigate this relationship, bFGF was evaluated in the Palmerston North autoimmune strain mouse, which develops otic capsule sclerotic lesions during the progression of its systemic disease. Inner ears from PN mice, along with control CBA/J and C3H/HeJ mice, were immunohistochemically stained with antibodies against bFGF to identify its presence and possible role in otic capsule disease. Although cells reactive for bFGF were observed along the lining of the otic capsule in all three strains, a significantly higher frequency was observed in the PN mice. Other sites of staining included connective tissue around the tensor tympani muscle and the geniculate ganglion. This identification of bFGF in the otic capsule raises the possibility that it may play some role in normal bone maintenance, as well as abnormal bone or connective tissue remodeling in autoimmune disease.

Histochemistry of otic capsule sclerotic lesions in Palmerston North autoimmune strain mice

Otic capsule osteogenesis is a common finding in temporal bones from autoimmune disease individuals. However, the underlying cellular mechanisms are poorly understood. Therefore, to better understand this relationship of autoimmune disease and otic capsule pathology, inner ear sclerotic lesions of the Palmerston North autoimmune disease mouse were histochemically stained to identify their content and potential osteogenic processes. Lesions stained positive for calcium, amyloid, fibrinoid, and glycoproteins (PAS), but negative for collagen, calcium oxalate, reticular fibers and glycosaminoglycans (Alcian Blue). Amyloid and fibrinoid deposition are associated with other immune disease, which suggests these local processes may provide a protein substructure that calcifies in lesion progression. Similar cellular mechanisms may underlie certain types or phases of human autoimmune otic capsule disease.

Pathology of the otic capsule

The otic capsule is unique in retaining calcified cartilage, known as globuli interossei, throughout life and shows changes consequently, which are peculiar to it. In Paget's disease of bone, the otic capsule appears resistant to involvement and this occurs with extensive disease at a late stage. In contrast, otosclerosis is a new bone formation of unknown cause that is limited to the otic capsule. In osteogenesis imperfecta, the poor formation of collagen leads to abnormally thin bony trabeculae with a poorly formed otic capsule. In osteopetrosis, the otic capsule is greatly expanded by increased globuli interossei, as a result of defective osteoclast function. When fractured the middle layer of the otic capsule does not form callus, but heals by fibrosis.

Type II collagen distribution in the ear of the guinea pig fetus

By using monoclonal antibodies to type II collagen and immunohistochemical techniques, we studied the distribution of type II collagen in the developing guinea pig ear. Type II collagen appearance and disappearance corresponded to cartilage development and resorption. Type II collagen was identified in Meckel's and Reichert's cartilages, the cartilage plate of the auricle and external acoustic meatus, the ossicles, eustachian tube cartilage, and the otic capsule. Type II collagen also appeared with the development of structures in noncartilaginous parts including the tympanic membrane, tympanic annulus, basilar membrane, spiral limbus, spiral ligament, and osseous spiral lamina, Rosenthal's canal, the maculae of the utricle and saccule, and the semicircular canal membrane, crista ampullaris, and endolymphatic duct. Type II collagen is distributed widely in the ear after the early stages of development. Thus, type II collagen should be considered an important structural component of the ear.

Autoimmune disease and cochlear pathology in the C3H/lpr strain mouse

The C3H/lpr autoimmune strain mouse is a model for spontaneous systemic lupus erythematosus. Inner ear structure and function were examined during systemic autoimmune disease progression to identify correlated auditory system pathology. Onset of the systemic disease occurred at 2-3 months of age and was characterized by elevated serum immune complexes, cryoglobulins, and antinuclear antibodies. Coincident with the onset of autoimmune disease was degeneration of the stria vascularis. Early edema of the stria occurred in the apex and progressed basalward with duration of the disease. By 10 months of age, stria vascularis area was smaller and auditory brainstem response thresholds were elevated. No degeneration of hair cells was seen at any age, suggesting that the stria vascularis may be the primary anatomic site of autoimmune auditory damage in this mouse model.

Otosclerosis--an inflammatory disease of the otic capsule of viral aetiology?

Fragments of otospongiotic and otosclerotic footplates were investigated by immunohistochemical methods. Antibodies IgG, IgA, IgM were found to be bound to the vascular connective tissue of the resorption lacunae, IgG also to osteocytes. The application of antibodies against mumps, measles and rubella antigens showed the expression of the relevant viral antigens in the large cells of the resorption lacunae, in the vascular connective tissue, and in osteocytes, osteoclasts and chondrocytes, present in or around the otospongiotic areas. In the sclerotic stage only the perivascular connective tissue and chondrocytes have expressed viral antigens whereas IgG was restricted to the osteocytes of the sclerotic focus and to the residual perivascular tissue. Two footplates with postinflammatory sclerosis serving as controls revealed only IgG in some chondrocytes. Healthy footplates showed neither a deposition of antibodies nor any expression of viral antigens. These results favour a viral aetiology of otosclerosis as an inflammatory vascular reaction of the otic capsule initiated or caused by the viruses of measles, rubella and mumps.

Thirty years of stapes surgery

The modern stapedectomy with prosthesis insertion and living oval window seal, like the modern cataract extraction with lens replacement, is now performed, very much the same, throughout the world. I have reviewed the evolution of stapes surgery during these last thirty years and tried to gain some agreement for several important facts about otosclerosis and several basic principals of stapes surgery. While a well-performed stapedectomy can eliminate the conductive component, the sensorineural hearing loss continues and, in about one-third, will progress till the patient, after age 65, must return to a hearing aid. A piston prosthesis gives the best hearing results: 0.6 mm diameter, when half the footplate is removed and a living oval window seal interposed, and 0.6 mm diameter when a small opening is made in the footplate obliterated by otosclerosis. I prefer a teflon prosthesis to stainless steel because it can be altered by the surgeon at operation, and vein as an oval window seal. I have presented a rare group of patients who develop facial palsy 5-1/2 days after uncomplicated stapedectomy, of whom all recover quickly and completely. I am confident that progress will continue to be made in the understanding of otosclerosis, and the performance of stapes surgery, but in these last thirty years we have made a good beginning.

Hyaluronate production by the inner ear during otic capsule and perilymphatic space formation

Otosclerosis has been hypothesized to result from a disorder of the extracellular matrix of the cartilaginous rests present in the adult temporal bone. Matrix relationship to bone formation and remodeling, as well as the fact that the pathogenesis of otosclerosis is expressed by the action of both of these processes, strongly suggests that more knowledge is needed about the process of otic capsule development. In pursuit of this goal, otic complexes were explanted from mouse embryos that ranged in age from 10.5 to 16 days old and were then exposed to 3H-glucosamine (50 microCi/ml) for 6 hours in vitro. Total labeled glycosaminoglycans (GAGs) and labeled hyaluronate content of each age group of otic explants were measured, and the results were compared to a developmental series of the otic regions of whole embryos stained with either toluidine blue or alcian blue. Increases in the synthesis of the total GAGs were observed on embryonic day 11 and for a prolonged period extending from gestation day 13.5 through day 16. The first increase of GAGs occurred at the initiation of metachromasia and positive staining by toluidine blue of the region of aggregated periotic mesenchyme cells that form the otic capsule. The second increase in GAGs was correlated with chondrification of the capsule. Hyaluronate production revealed a different pattern. Synthesis of hyaluronate exhibits peaks at 10.5, 12.5, and for an extended period of from 13.5 to 14.5 days of gestation.(ABSTRACT TRUNCATED AT 250 WORDS)