(PP1602) Late-Onset Auditory Neuropathy Spectrum Disorder: Myth or Fact--Evidence from Non- Auditory and Audiological Test Battery

The study explored the differences in audiological and non-audiological characteristics between congenital and late-onset auditory neuropathy spectrum disorder (ANSD). The participants were divided into three groups congenital ANSD – children  (30 individuals; 60 ears, < 12 y), adults (age ≥ 12y) with early-onset ANSD (onset of symptoms in childhood, 30 individuals; 56 ears), and adults with late-onset ANSD (onset after 12 y, 35 individuals; 62 ears). The differences could be because of variation in etiology, pathophysiology, site of lesion, or genetic variability between the congenital and late-onset group, which needs to be further studied in detail.

Summary: 

Rationale: Despite the advantage of embarking onset-based differences in auditory rehabilitation, scanty literature has focused on profiling the auditory and non-auditory characteristics of congenital and late-onset ANSD. The profiling of such characteristics can cluster factors that Audiologists should pay attention to delineate ANSD onset-based group differences. The study explored the differences in audiological and non-audiological characteristics between congenital and late-onset auditory neuropathy spectrum disorder (ANSD).

Design: Ninety-five individuals diagnosed with ANSD were included in the study. The participants were divided into three groups congenital ANSD – children  (30 individuals; 60 ears, < 12 y), adults (age ≥ 12y) with early-onset ANSD (onset of symptoms in childhood, 30 individuals; 56 ears), and adults with late-onset ANSD (onset after 12 y, 35 individuals; 62 ears). The mean age of the congenital ANSD – children group was 3.17± 1.99 y, while adult early-onset and late-onset ANSD groups were 21.32 ± 7.75 y and 23.16 ± 7.55 y, respectively. The retrospectively collected data of both non-audiological and audiological measures were compared between the three groups.The non-audiological characteristics included gender, laterality and risk factors, while the audiological characteristics comprised ofbehavioral (pure tone and speech audiometry), physiological (Immitance, OAE and reflexes) and electrophysiological (ABR, LLR, CM whichever available) measures.

Results and

Discussion: The results of the study showed that females in the late-onset adultsgroup were more affected than males by a ratio of 2.1: 1. Such pronounced differences in gender ratio was not seen in both congenital (children) and early-onset adult groups. Audiological test findings revealed the pure tone and speech thresholds of congenital and ANSD group were significantly higher [Kruskal Wallis test:χ²(2) = 52.04, p< 0.001, followed by post-hoc) compared to the late-onset ANSD group. While spared inner hair cell (IHC) functions due to delayed onset can be speculated to the better auditory thresholds in late-onset group, congenital and early onset groups predominantly have overall IHC damage due to long standing disorder. The former groups also demonstrated predominantly flat audiogram, while the latter group had raising configuration.Poor phase-locking (typically low-frequency auditory nerve fibres) in late-onset ANSD, could have resulted in rising audiogram in them. On other hand, flat audiogram in the congenital-ANSD group and adults with early-onset ANSD suggests a lesion more at the level of IHC or synapse leading to hearing loss at all the frequencies.

In addition, all the three groups exhibited similarities in ABR, OAE and immittance characteristics. In contrast, late-onset ANSD demonstrated less affected latency and amplitude of LLR, indicating better cortical processing in them than the congenital/ early-onset ANSD group. Results of Fischer’s discriminant analyses showed that the pure tone average, the configuration of hearing loss, and speech thresholds are good metrices of onset-related group differences.

Conclusions: The study highlights the non-audiological and audiological differences between congenital and late-onset ANSD groups. These differences could be because of variation in etiology, pathophysiology, site of lesion, or genetic variability between the congenital and late-onset group, which needs to be further studied in detail.