Abstract
Auditory neuropathy spectrum disorder (ANSD) is a retrocochlear disorder in which cochlear functioning is normal but the transmission in the auditory neural pathway is affected. The present study reports of neural fatigue seen in subjective and objective tests of adaption in a 19 year old adult with ANSD. He had bilateral mild sensorineural hearing loss with otoacoustic emissions present and absent auditory brainstem response. Immittance evaluation showed elevated acoustic reflexes at 500 Hz and 1000 Hz in both ipsilateral and contralateral stimulation. Reflex decay test was administered at 500 Hz and 1000 Hz which showed positive reflex decay with contralateral stimulation. Olsen and Noffsinger tone decay test and supra-threshold adaptation test showed positive tone decay at 500 Hz, 1000 Hz and 2000 Hz in both ears. The results of the study showed positive reflex decay and positive tone decay which indicate abnormal neural fatigue. The abnormal neural firing seen in individuals with ANSD could have resulted in positive reflex decay and tone decay. However, further studies on larger group of population are essential for further understanding the mechanisms in detail.
Highlights
Auditory neuropathy spectrum disorder (ANSD) is a defined as a retrocochlear disorder in which patient has normal otoacoustic emissions/cochlear microphonics and absent/abnormal auditory brainstem response (ABR) [1,2,3,4,5]
The abnormal neural firing seen in individuals with ANSD could have resulted in positive reflex decay and tone decay
There are very limited studies reported in the literature which have attempted to determine acoustic reflex decay when reflexes are present in individuals with ANSD
Summary
Auditory neuropathy spectrum disorder (ANSD) is a defined as a retrocochlear disorder in which patient has normal otoacoustic emissions/cochlear microphonics and absent/abnormal auditory brainstem response (ABR) [1,2,3,4,5]. Narne et al [8] reported that 198 patients with ANSD in their study had absent acoustic reflexes in both ears. There are very limited studies reported in the literature which have attempted to determine acoustic reflex decay when reflexes are present in individuals with ANSD. The present study attempts to report a unique case with auditory neuropathy spectrum disorder who presents abnormal neural fatigue in subjective and objective tests. The speech identification scores were 96% in right ear and 56% in left ear He had ‘A’ type tympanogram with acoustic reflexes present but elevated at 500 Hz and 1000 Hz in both ipsilateral and contralateral stimulation. Olsen and Noffsinger tone decay test was tested in both ears by presenting tones of 500 Hz, 1000 Hz and 2000Hz at 20 dB SL He was instructed to keep pressing the patient response switch till he hears the sound. To confirm the positive STAT results, pulsed tones were presented and he was able to hear the tones for one minute
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