الفهرس 
INTRODUCTION AND RATIONALEOnly 14 pages are availabe for public view
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Abstract
Auditory neuropathy spectrum disorder (ANSD) is a condition caused by a deficiency of synchronous neural activity of the cochlear nerve and is related to injuries that can affect the inner hair cell synapse, spiral ganglion, axon, the myelin sheath, and/or nerve dendrite (Nikolopoulos, 2014). Although auditory neuropathy was formally defined around 20 years ago, this form of hearing loss continues to cause controversy and challenges in decision making over appropriate means of habilitation.
Cochlear implantation may be an option for hearing rehabilitation. Although the outcome of cochlear implantation in children with AN/AD might vary, it is favorable in most cases. Cochlear implantation seems a justified hearing rehabilitation option for children with AN/AD and limited benefits from conventional hearing aids.
Psychophysical measures can be used to study performance variability. Cortical auditory evoked potentials (CAEPs) are objective tests that reflect the neural detection and/or discrimination of sound underlying speech perception. Therefore, it is beneficial to assess outcome variability with CI. CAEPs include obligatory evoked potentials such as P1, N1, and P2, and discriminative potentials such as Acoustic change complex (ACC), mismatch negativity (MMN) and P300. The latency and morphology of CAEP can provide information about the maturation of central auditory pathways (Sharma et al., 2004).
Moreover, complex auditory brainstem response (c-ABR) reliably measures the brainstem timing and provides valuable information about pitch and harmonic encoding (King et al., 2002). In the normally perceiving auditory system, stimulus timing, on the order of fractions of milliseconds, is accurately and precisely represented at the level of the brainstem (Skoe and Kraus, 2010). So, it is conceivable that c-ABR could serve as an objective measure for assessment of auditory temporal processing abilities. Complex-ABR is a test used for investigation of learning disability, developmental plasticity, and language processing skills (Sinha & Basavaraj, 2010).
This study was designed to investigate CAEP and c-ABR in ANSD subjects fitted with CIs and to compare results of both tests in ANSD with SNHL subjects fitted with CIs. Hopefully, this will aid in addressing the variability in performance in CI subjects as objective electrophysiological tests pose a potential alternative to behavioral testing when young implanted children are being evaluated.
The study group consisted of twenty nine unilaterally implanted subjects, they were subdivided into two subgroups: ANSD Group: it compromised thirteen subjects, age ranged from 3.2 to 29 years with mean of (9.3 years). SNHL Group: it compromised sixteen subjects, age ranged from 2.9 to 15.5 years with mean of (7.7 years). The normal hearing control group consisted of sixteen subjects, age ranged from 5 to 29.5 years with mean of (11.1 years).
For all subjects participating in the study, sound field evaluation using warble tones 250-8000 Hz including the mid octave frequencies via 2 channel AC40 audiometer and speech reception threshold were performed. P1 cortical auditory evoked potentials (CAEP) and complex ABR using synthetic speech syllables (da) at intensity of 40 dB sensation level (above aided SDT/SRT threshold) were recorded using Bio-logic Navigator Pro Auditory Evoked Potential (AEP) System (version 7.0.0) connected to a loudspeaker to collect and analyze the waveforms. The tests were conducted for the implanted subjects while wearing their CIs.
The results showed that CAEP P1 was detected in all subjects and different patterns had been encountered reflecting maturation of P1. The study and control groups did not show single type of waveform morphology as three types were presented in both. The majority of ANSD group (8 subjects, 61.5%) and SNHL group (14 subjects, 87.5%) showed the child waveform morphology (P1 & P1N2). Contrary to this, the majority of normal hearing control group (10 subjects, 62.5%) showed adult form P1N1P2 /P1N1P2N2 complex. The normal hearing control group showed significant better shorter latency than the study groups in onset P1 response. However, there were no statistically significant differences between ANSD group and SNHL group in p1 latency.
Complex-ABR could be successfully recorded in ANSD wearing CI using relatively long stimuli (da 150 msec long). c-ABR waves were detected in 53.8% of ANSD subjects and 75% of SNHL subjects fitted with CI, while it was detected in all normally hearing subjects. Both study subgroups had prolonged onset and offset responses evidenced by shifted waves V, A and O than the control group. ANSD & SNHL groups were further subdivided into detected c-ABR and absent c-ABR subgroup. There was a statistically significant difference between detected c-ABR and absent c-ABR subgroup subjects in discrimination score, MAIS Score and APHAB Score in SNHL group. There was also a statistically significant difference between detected c-ABR and absent c-ABR subgroup subjects in discrimination score and MAIS Score in ANSD group. However, there was no significant difference between detected c-ABR and absent c-ABR subgroup in APHAB Score in ANSD group. Accordingly, the presence of c-ABR waves is proved to be a good predictor tool for better cochlear implant outcome measures in children.
In conclusion, outcomes of CI in subjects with ANSD are comparable with subjects with profound cochlear loss, and therefore, this may suggest that CI is a successful rehabilitative intervention procedure in some of the ANSD subjects and has a definite role in regaining hearing and development of speech.