The Incudomalleolar Articulation in Down Syndrome (Trisomy 21): A Temporal Bone Study

Hypothesis One reason for conductive hearing loss (HL) in patients with Down syndrome (DS) is structural anomalies in the incudomalleolar joint (IMJ) that impair sound transmission. Background The majority of hearing losses in patients with DS are conductive. One reason is the high incidence of inflammatory processes such as otitis media. However, in some patients, the middle ear seems to be normal. The assumption of structural disorders causing a HL is supported by a previous study revealing structural abnormalities of the incudostapedial joint (ISJ) in these patients. Methods In a retrospective analysis, histologic sections of the IMJ of 16 patients with DS were compared with 24 age- and sex-matched subjects with normal middle ear ossicles. The length of 8 parameters of the IMJ were measured at 3 positions and compared between the 2 groups. Results Age (p = 0.318) and sex distribution (p = 1) for the DS group and the matched controls were comparable. The IMJs (p < 0.001) and the cartilage of patients with DS are significantly wider in most measurements compared with controls. However, the joint space is not significantly different in the 2 groups. Conclusion Conductive HL might be caused by a significantly wider IMJ in patients with DS supporting the findings of a previous study reporting similar findings for the ISJ. The etiology of these findings is unclear. Patients with DS have a high prevalence of deficient collagen synthesis. Immunohistochemical analysis may be needed to investigate the collagen structure of the ISJ and IMJ in patients with DS.