Abnormalities of cilia in the middle ear in chronic otitis media

Whole exome sequencing study identifies candidate loss of function variants and locus heterogeneity in familial cholesteatoma

Cholesteatoma is a rare progressive disease of the middle ear. Most cases are sporadic, but some patients report a positive family history. Identifying functionally important gene variants associated with this disease has the potential to uncover the molecular basis of cholesteatoma pathology with implications for disease prevention, surveillance, or management. We performed an observational WES study of 21 individuals treated for cholesteatoma who were recruited from ten multiply affected families. These family studies were complemented with gene-level mutational burden analysis. We also applied functional enrichment analyses to identify shared properties and pathways for candidate genes and their products. Filtered data collected from pairs and trios of participants within the ten families revealed 398 rare, loss of function (LOF) variants co-segregating with cholesteatoma in 389 genes. We identified six genes DENND2C, DNAH7, NBEAL1, NEB, PRRC2C, and SHC2, for which we found LOF variants in two or more families. The parallel gene-level analysis of mutation burden identified a significant mutation burden for the genes in the DNAH gene family, which encode products involved in ciliary structure. Functional enrichment analyses identified common pathways for the candidate genes which included GTPase regulator activity, calcium ion binding, and degradation of the extracellular matrix. The number of candidate genes identified and the locus heterogeneity that we describe within and between multiply affected families suggest that the genetic architecture for familial cholesteatoma is complex.

A new theory interprets the development of a retraction pocket as a natural self-healing process

PURPOSE

The thesis that cholesteatoma evolves from a retraction pocket is widely accepted today. Yet, its prime etiology, the question of what triggers the invagination of healthy skin, still remains unclear despite centuries of investigations into the origin of cholesteatoma. A new idea interprets the horizontal migration of skin into the middle ear cavities as a self-healing process, curing an underlying inflammation in the tympanic cavity, through the overgrowth and contact with immunologically active tissue.

METHODS

A retrospective analysis of the interrelation of retraction pockets and underlying granulation tissue was conducted in 209 second-look cholesteatoma surgeries over the last decade.

RESULTS

A stable tympanic membrane over aerated, healthy middle ear mucosa was found in 71.3% of cases. In 11%, small retractions with air in other parts of the middle ear cleft (epitympanic, sinus or anterior mesotympanum) were described. In 6.2%, granulations under a retraction were found. Only 3.8% of the reports revealed air behind a retraction or did not provide enough information on the mucosa situation behind the drum membrane.

CONCLUSIONS

A new hypothesis interprets the origin of a retraction pocket-the precursor of a cholesteatoma-as a natural attempt by the body to cure an underlying inflammation in a cavity. Analogous phenomena exist, e.g. the migration of the omentum towards a local inflammation in the abdomen. This idea, which is supported by the findings in our 209 second-look surgeries, is the first explanation of the origin of retraction pockets that is compatible with the various characteristics of original or recurrent cholesteatoma. A prophylaxis against a recurrent cholesteatoma might be attained by securing free drainage of the mucosa into the tubal orifice with the use of thin silicone foils in an attempt to prevent any granulation in the middle ear cleft, similar to the principles of modern rhinosinusoidal surgery with its emphasis on unblocked mucosa clearance. This allows gas production in the healed middle ear mucosa to recover, reducing the risk of a recurrent retraction.

A defect in early myogenesis causes Otitis media in two mouse models of 22q11.2 Deletion Syndrome

Otitis media (OM), the inflammation of the middle ear, is the most common disease and cause for surgery in infants worldwide. Chronic Otitis media with effusion (OME) often leads to conductive hearing loss and is a common feature of a number of craniofacial syndromes, such as 22q11.2 Deletion Syndrome (22q11.2DS). OM is more common in children because the more horizontal position of the Eustachian tube (ET) in infants limits or delays clearance of middle ear effusions. Some mouse models with OM have shown alterations in the morphology and angle of the ET. Here, we present a novel mechanism in which OM is caused not by a defect in the ET itself but in the muscles that control its function. Our results show that in two mouse models of 22q11.2DS (Df1/+ and Tbx1(+/-)) presenting with bi- or unilateral OME, the fourth pharyngeal arch-derived levator veli palatini muscles were hypoplastic, which was associated with an earlier altered pattern of MyoD expression. Importantly, in mice with unilateral OME, the side with the inflammation was associated with significantly smaller muscles than the contralateral unaffected ear. Functional tests examining ET patency confirmed a reduced clearing ability in the heterozygous mice. Our findings are also of clinical relevance as targeting hypoplastic muscles might present a novel preventative measure for reducing the high rates of OM in 22q11.2DS patients.

The ciliary beat frequency of middle ear mucosa in children with chronic secretory otitis media

The chronic secretory otitis media (CSOM) is a common disease in children. Its cardinal symptoms are recurrent middle ear effusions and conductive hearing loss. Until today, the pathophysiological mechanism of this disease remains unknown. The correlation with adenoids and tubal dysfunction during childhood seems to be obvious, but the origin of middle ear effusions still has to be clarified. It is known that the CSOM affects the mucociliary system in several ways. In order to find out more about these correlations, the ciliary beat frequency was examined in 123 samples of infantile middle ear mucosa suffering from CSOM. Samples were surveyed using a stroboscopic microscopy method. The results of this study showed a significant decrease of ciliary beat frequency (CBF) to an average of 7.4 s(-1) in children with a CSOM. The healthy group of control showed a frequency of 10.1 s(-1). The measured CBF dataset was correlated with microbiological findings. We found a typical bacterial profile in nearly all the cases that were examined but were unable to find a specific bacterium decreasing CBF. This study provides evidence for the diminution of CBF in cases of CSOM in comparison to a healthy control group. Our findings emphasize the importance of stopping the vicious circle of recurrent effusions by paracentesis or grommet insertion.

Ultrastructure of eustachian tube mucosa in chronic otitis media with cholesteatoma

PURPOSE

Acquaintance with the severity of inflammatory condition and mucociliary destruction of the protympanic eustachian tube (ET) mucosa may provide some insight for management during surgery for cholesteatoma.

MATERIALS AND METHODS

Protympanic eustachian mucosa was obtained from 25 patients undergoing ear surgery for cholesteatoma and from 5 cadavers undergoing dissection for a gross anatomy course. The specimens were processed for both scanning electron microscopy (SEM) and transmission electron microscopy (TEM).

RESULTS

According to SEM, decreased ciliated cells were noted. Residual ciliated cells and numerous white blood cells (WBC) were noted in the protympanic mucosa of the eustachian orifice. Bacilli were commonly noted at the mucosal surface. Cilia might be collapsed and stagnated with mucus secretion. This finding was consistent with those of the TEM: that cilia of varied directions were embedded in mucus. Mucociliary function was impaired under such conditions. The mucosal alteration was severe in some children; there was no ciliated cell visible. According to the TEM, the mucosal cells contained numerous secretory granules and mitochondria. Polymorphous nuclear cells were noted in the submucosal area that was edematous. Compound cilia were rather common. Mucus blanket covered mucosal cells with widening intercellular spaces. In addition, neither cilia nor microvilli were visible in severe mucosal alteration.

CONCLUSIONS

These occurrences indicated the presence of inflammatory reaction and impairment of clearance function of eustachian mucosa in cholesteatomatous ears. Thorough irrigation during surgery and antimicrobial therapy after surgery are warranted.