Supervisors info:
Νικολόπουλος Θωμάς, Καθηγητής, Ιατρική Σχολή, ΕΚΠΑ
Μαραγκουδακης Παυλος Επίκουρος Καθηγητής, Ιατρική Σχολή, ΕΚΠΑ
Δελιδης Αλεξανδρος, Επίκουρος Καθηγητής, Ιατρική Σχολή, ΕΚΠΑ
Summary:
Introduction
Auditory neuropathy (AN) or auditory neuropathy spectrum disorder (ANSD) is a recently described form of hearing impairment where neural dys-synchrony and deterioration of temporal processing is the predominant characteristic. This condition is a clinical entity which is caused by abnormal neural encoding of sound stimuli despite preservation of sensory transduction and amplification by the outer hair cells. Auditory neuropathy can be caused by damage to the sensory inner hair cells, IHC ribbon synapses or spiral ganglion neurons.
Objective
This review of the literature aims to attain all available published evidence on auditory neuropathy in order to provide an update on recently elucidated pathophysiological mechanisms such as sensory, synaptic and neural mechanisms of this disease. The corresponding clinical findings and diagnostic criteria of AN will be identified and current rehabilitation strategies as well as future therapies will be discussed. Moreover, the role and the benefits of cochlear implantation (CI) in AN individuals will be evaluated in order to answer one clinical question: For individuals with the diagnosis of an auditory neuropathy, what is the effect of cochlear implantation on hearing and communication skills?
Methods
A review of the literature was conducted using the PUBMED, EMBASE, ERIC (Education Resources Information Center) and COCHRANE CENTRAL databases to encompass English and Greek articles from 1990 to January 2019. Terms such as “auditory neuropathy”, “auditory, neuropathy spectrum disorder”, and AN linked with key words such as “epidemiology”, “etiology”, “pathophysiology”, “diagnosis”, “management” and “cochlear implants” were used. The selection of articles followed screening for eligibility for inclusion, based on issues related to the objective of this review of the literature.
Results
A total of 299 studies that illustrate their insight on the diagnosis, pathophysiology, epidemiology, the risk factors and the etiology of auditory neuropathy were included in this literature review. 75 studies were included in the literature review, applicable to answer the posed question, regarding cochlear implants and their effects on hearing and communication skills in patients with AN. A total of 57 articles reported a significant advantage in the management of auditory neuropathy with CI, presenting improved auditory skills and language development in implanted AN patients. The remaining 17 studies demonstrated that although cochlear implantation offers the possibility of speech perception and improved hearing skills to subjects with AN, the benefit depends on the site of the lesion and confounding disorders.
Conclusion
Auditory neuropathy is not a rare disorder, especially amongst hearing-impaired children. The absence of an auditory brainstem response (ABR) and the presence of otoacoustic emissions (OAE) indicate an AN profile, but determining the exact anatomical site of the disorder, requires more in-depth audiological and electrophysiological tests combined with imaging and genetic evaluations. Timely and adequate treatment is of utmost importance, even though it still remains a challenge for the clinicians, as current hearing aid technology is not able to enhance the temporal envelope of the speech signal to compensate for temporal processing deficits associated with AN. The data gleaned in this review of the literature support the conclusion that cochlear implantation (CI) positively affects hearing and communication skills in AN individuals and even patients with mild to moderate hearing abilities with poor speech intelligibility, should be candidates for CI as they will benefit significantly in improved conversational speech discrimination post-surgically. However due to the heterogeneity of this disorder special consideration is required when undertaking hearing rehabilitation and cochlear implantation in AN patients.
Keywords:
Auditory neuropathy, Auditory dys-synchrony, Hearing aids, Cochlear implants.
