It has become clear that early auditory skill development after Cochlear Implant (CI) surgery differs according to the cause of hearing loss. The genetic hearing loss group was found to show the best results in terms of auditory development behavior, followed by the unknown cause, cCMV infection, inner ear malformation, syndrome deafness, and cochlear nerve hypoplasia groups. However, even with hearing loss due to the genetic causes, for which CI is highly effective, the auditory behavior differs considerably. Individual (re)habilitation programs are needed to ensure better language development for each patient.

Early auditory skill development after CI

CI is an effective treatment option for severe-to-profound hearing loss patients, with the insertion of the electrode into the cochlea and direct electrical stimulation of the auditory nerve. CI is currently used as the standard therapeutic option for severe-to-profound sensorineural HL patients worldwide.

However, the outcomes of CI vary among patients. Various factors affect CI outcomes, including early CI, bilateral CI, communication mode, parent-child interaction rating, socioeconomic status, other associated symptoms and inner ear malformation or cochlear nerve deficiencies.

We performed a comprehensive study on the etiology of patients receiving CI. As a result, we identified the etiology of hearing loss in 85% of congenital hearing loss CI patients and 42% of late onset CI patients (Miyagawa et al., Otol Neurotol. 2016, Figure 1). In addition, we revealed that patients with genetic causes involving an ‘intra-cochlear’ etiology showed better CI outcomes than did patients with other etiologies (Miyagawa et al., Otol Neurotol. 2016, Figure 2)

Figure 1. Etiology of CI/EAS patients. (A) Prelingual CI/EAS patients (n 1⁄4 88). Blue indicates syndromic hearing loss; gray, unkown; green, infection-induced hearing loss; orange, inner ear anomaly; pink, nonsyndromic hearing loss associated with specific gene mutations. (B) Postlingual CI/EAS patients (n1⁄477). Blue indicates acoustic tumor; gray, unkown; green, otosclerosis; orange, otitis media; pink, nonsyndromic hearing loss associated with specific gene mutations.

Figure 2. Early auditory development assessed using the LittlEARS auditory questionnaire. (A) Nonsyndromic hearing loss with specific gene mutations (n 1⁄4 11). (B) Other etiology (n 1⁄4 11). Blue indicates syndromic hearing loss; gray, unkown; green, infection-induced hearing loss; pink, nonsyndromic hearing loss associated with specific gene mutations.

Large cohort study of pediatric CI patients

We performed a larger scale, multi-center retrospective epidemiological survey for pediatric CI patients. Further, in this study, we analyzed the clinical features for each etiological group as well as the effects of etiology on CI outcomes in terms of early auditory skill development as measured by Infant Toddler-Meaningful Auditory Integration Scale (IT-MAIS) and Meaningful Use of Speech Scale (MUSS), total development as measured by the Kyoto Scale of Psychological Development 2001 (KSPD) and Wechsler Intelligence Scale for Children (WISC-IV), monosyllable perception, speech intelligibility rating (SIR) and vocabulary development at school age as measured by the revised version of the Picture Vocabulary Test (PVT-R) and Word Fluency Test (WFT).

As a result, we clarified the etiology of hearing loss in 71% of participant, with the most common etiology for pediatric CI patients being genetic causes (Nishio et al., Acta Otolaryngol. 2022. Figure 3). The genetic etiology group showed the most favorable development in terms of IT-MAIS and MUSS score after CI, followed by the unknown etiology group, syndromic HL group, cCMV group, inner ear malformation group, and cochlear nerve deficiency group (Nishio et al., Acta Otolaryngol. 2022. Figure 4). These differences were still observed in vocabulary development as measured by PVT-R and WFT in school age.

Figure 3. Etiology of Japanese CI children (n 1⁄4 308). Orange indicates non-syn- dromic hearing loss associated with specific gene mutations, green indicates syndromic HL, blue indicates inner ear anomalies, light blue indicates cochlear nerve deficiencies, yellow indicates congenital CMV infection- or mumps-associ- ated HL, and gray indicates the patients with unknown etiology.