Auditory neuropathy (AN) is a clinical disorder characterized by the absence of auditory brainstem response and presence of otoacoustic emissions. A gradual loss of otoacoustic emissions has been reported for some cases of AN. Such cases could be diagnosed as cochlear hearing loss and lead to misunderstanding of the pathology when patients first visit clinics after the loss of otoacoustic emissions. The purpose of this study was to investigate the time course of changes in distortion product otoacoustic emissions (DPOAEs) in association with patients’ genetic and clinical backgrounds, including the use of hearing aids.
DPOAE measurements from 31 patients with AN were assessed. Genetic analyses for GJB2, OTOF, and mitochondrial m.1555A> G and m.3243A> G mutations were conducted for all cases, and the analyses for CDH23 and OPA1 were conducted for the selected cases. Patients who were younger than 10 years of age at the time of AN diagnosis were designated as the pediatric AN group (22 cases), and those who were 18 years of age or older were designated as the adult AN group (9 cases). DPOAE was measured at least twice in all patients. The response rate for DPOAEs was defined and analyzed.
The pediatric AN group comprised 10 patients with OTOF mutations, 1 with GJB2 mutations, 1 with OPA1 mutation, and 10 with indefinite causes. Twelve ears (27%) showed no change in DPOAE, 20 ears (46%) showed a decrease in DPOAE, and 12 ears (27%) lost DPOAE. Loss of DPOAE occurred in one ear (2%) at 0 years of age and four ears (9%) at 1 year of age. The time courses of DPOAEs in patients with OTOF mutations were divided into those with early loss and those with no change, indicating that the mechanism for deterioration of DPOAEs includes not only the OTOF mutations but also other common modifier factors. Most, but not all, AN patients who used hearing aids showed deterioration of DPOAEs after the start of using hearing aids. A few AN patients also showed deterioration of DPOAEs before using hearing aids. The adult AN group comprised 2 patients with OPA1 mutations, 2 with OTOF mutations, and 5 with indefinite causes. Four ears (22%) showed no change in DPOAE, 13 ears (72%) showed a decrease, and one ear (6%) showed a loss of DPOAE. Although the ratio of DPOAE decrease was higher in the adult AN group than in the pediatric AN group, the ratio of DPOAE loss was lower in the adult AN group. DPOAE was not lost in all four ears with OPA1 mutations and in all four ears with OTOF mutations in the adult group.
DPOAE was decreased or lost in approximately 70% of pediatric and about 80% of adult AN patients. Eleven percent of pediatric AN patients lost DPOAEs by 1 year of age. Genetic factors were thought to have influenced the time course of DPOAEs in the pediatric AN group. In most adult AN patients, DPOAE was rarely lost regardless of the genetic cause.
1Division of Hearing and Balance Research, National Institute for Sensory Organs, National Hospital Organization Tokyo Medical Center, Tokyo, Japan
2Department of Otolaryngology-Head and Neck Surgery, Faculty of Medicine and Graduate School of Medicine, Hokkaido University, Hokkaido, Japan
3Department of Otorhinolaryngology, National Center for Child Health and Development, Tokyo, Japan
4Division of Otorhinolaryngology, Chiba Children’s Hospital, Chiba, Japan
5Department of Otolaryngology, Kanto Rosai Hospital, Kanagawa, Japan
6Department of Otorhinolaryngology, National Hospital Organization Mie Hospital, Mie, Japan
7Department of Otorhinolaryngology, Inagi Municipal Hospital, Inagi, Tokyo, Japan
8Department of Otolaryngology, Kobari General Hospital, Chiba, Japan
9Department of Otorhinolaryngology, Hyogo Prefectural Kobe Children’s Hospital, Hyogo, Japan
10Department of Otolaryngology, Sapporo Medical University School of Medicine, Sapporo, Japan
11Medical Genetics Center, National Hospital Organization Tokyo Medical Center, Tokyo, Japan.
Received October 14, 2016; accepted February 20, 2018.
This work was supported by a Grant-in-Aid for Clinical Research from the National Hospital Organization [H27-NHO (Kankaku)-02].
The authors have no conflicts of interest to declare.
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Address for correspondence: Tatsuo Matsunaga, Division of Hearing and Balance Research, National Institute of Sensory Organs, 2-5-1 Higashigaoka, Meguro, Tokyo 8902, Japan. E-mail: email@example.com