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Few data are available regarding long-term outcomes in patients with auditory neuropathy (AN), absent auditory brainstem responses (ABRs) despite normal cochlear function.1,2 In 1993 we described an 18-year-old woman with AN and normal hearing thresholds, normal otoacoustic emission test results, and absent ABRs.3
We retested her at age 24 years. Audiological results were identical (Figure 1).4 Background noise severely impaired word recognition.
Patient audiograms at ages 18, 24, and 41 years. A mild high-frequency hearing loss hearing loss emerged at age 41 years. Air-conduction thresholds are shown (right ear in orange, left ear in gray) and bone conduction (blue triangles).
Herein we report results when the patient was aged 41 years. The patient provided written consent, and the Northwestern University institutional review board approved study procedures. The patient has pursued a successful career and raised a family despite continued difficulties hearing in noise. She struggles to understand unfamiliar accents; yet, she is English-Hebrew bilingual and understands Israeli accents well. She described inconsistent sound awareness, particularly for alarms, such as phones and doorbells.
The patient’s air-conduction thresholds had increased in the interim (approximately +10 dB HL from 0.5-4 kHz) and were consistent with a mild high-frequency hearing loss, although still relatively normal (Figure 1). Distortion product otoacoustic emissions (DPOAEs) were robust bilaterally, and were approximately 12 dB signal-to-noise ratio (SNR) on average (compared with approximately 20 dB previously4); ABRs remained absent bilaterally.
Sentence perception in sound field was measured with the Hearing in Noise Test (HINT). In quiet, the patient did not notice sentences until 39.1 dB SPL (<1st percentile) but, once she heard the sentences, she understood 100% of the words. The patient’s speech reception threshold (SRT) in noise was +2 dB signal-to-noise ratio (SNR, <1st percentile). When the speech and noise sources were separated by 180°, her SRT improved to −2.9 dB SNR (noise right/speech left) and −1.2 dB SNR (noise left/speech right), indicating a spatial release from masking of 3.2 to 4.9 dB. Rance et al5 reported a spatial release of 7.6 dB (range, 0-13 dB) in patients with AN.
The HINT was conducted under headphones with speech and noise colocated (SRT, +4.5 dB SNR; <1st percentile). Performance was worsened by applying amplification algorithms to the speech signal to improve audibility (National Acoustics Lab-Revised +7.2 dB SNR; House Ear Amplification Routine: +6.2 dB SNR; both <1st percentile). The QuickSIN measured sentence recognition under headphones. The patient’s average SNR loss was 10 dB and 13.5 dB in the right and left ears, respectively. Diotically, the patient scored 1.5 dB on the first run (within normal range) and 7.5 dB on the second (Figure 2).
HINT indicates Hearing in Noise Test; HEAR, House Ear Amplification Routine; NAL, National Acoustics Lab-Revised; SNR, signal-to-noise ratio. A, The patient's performance on the HINT in sound field under different spatial listening conditions. Error bars represent across-trial variability on the test. B, The performance on the HINT under headphones; performance was worse when amplification routines were applied to compensate for her mild hearing loss. Error bars represent across-trial variability on the test. C, The patient’s performance on the QuickSIN, showing the proportion of words she successfully identified at each SNR. Her performance improved when sentences were presented binaurally. D, The QuickSIN SNR loss score for each hearing condition, with higher scores indicating worse performance. Two sentence sets were delivered for each listening condition (right ear, left ear, and binaurally), with performance on both plotted. The gray lines show the range of scores considered a mild SNR loss on the test. Performance was more variable on the binaural listening condition, with performance reaching normal range on 1 test run.
We know of 1 other long-term follow-up in a patient with AN, who as a young adult who had normal thresholds but 22 years later developed moderate-to-severe hearing loss.6 Although the case presented herein is subtler, elevated hearing thresholds are consistent. Paradoxically, the patient’s DPOAEs were present in this frequency range. She noted a buzzing sound when certain audiogram tones were presented, which may have caused masking. Poor awareness of quiet sounds may affect her performance. Still, DPOAEs were lower than in our previous report.4
This patient’s speech-in-noise perception improved when she listened with 2 ears, likely owing to interaural level differences (better ear effect). Importantly, her performance worsened under the HINT amplification condition.
This follow-up motivates new hypotheses about AN and its treatment:
A lack of synchrony prevents triggering protective mechanisms in noise (middle ear and medial olivocochlear reflexes), accounting for elevated hearing thresholds and decreased DPOAEs, indicating accelerated onset of age-related hearing loss. Alternatively, quiet sounds are easily masked and difficult to detect, accounting for the discrepancy between audiometry and DPOAEs.
Subtle, albeit diminished, binaural cues improve perception in noise. Screening for residual binaural sensitivity might be important when evaluating a patient with AN’s candidacy for hearing aids and/or cochlear implants.
The patient’s ability to learn a new accent suggests auditory processing is amenable to training in patients with AN.
To the extent this patient’s case generalizes, her follow-up illuminates the possibilities and persistent challenges endemic to AN.
Corresponding Author: Nina Kraus, PhD, Departments of Neurobiology & Otolaryngology, Northwestern University, 2240 Campus Dr, Evanston, IL, 60208 (firstname.lastname@example.org).
Published Online: March 12, 2020. doi:10.1001/jamaoto.2019.4314
Conflict of Interest Disclosures: Dr Kraus reported grants from Knowles Hearing Center during the conduct of the study. No other disclosures were reported.
Additional Contributions: We thank the patient for granting permission to publish this information.
Funding/Support: Supported by the Knowles Hearing Center.
Role of the Funder/Sponsor: The Knowles Hearing Center had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.
White-Schwoch T, Anderson S, Kraus N. Long-term Follow-up of a Patient With Auditory Neuropathy and Normal Hearing Thresholds. JAMA Otolaryngol Head Neck Surg. Published online March 12, 2020. doi:10.1001/jamaoto.2019.4314
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