Sunday 30 June 2013

Confusion from Ear-Brain Dissociation

Auditory neuropathy spectrum disorders (ANSD) is an interesting relatively recent diagnosis whose recognition was made possible by advances in electrophysiologic acoustic measurement, specifically the ABR and the OAE. However the interesting fact was the first audiologic description of ANSD was believed to be by Hinchcliffe et al in 1972, six years before Kemp described Otoacoustic emissions. 
ANSD is characterized by normal OAES, presence of cochlear microphonics, absent middle ear muscle reflexes at 95 dB and below, and abnormal ABR. In simple terms, the brain in ANSD appears to be detached from the auditory pathway and /or the inner ear appears not to communicate with the auditory nerve (depending on the variant). 
ANSD is believed to consist of variant of disorders with lesions in either of several locations - inner hair cells, inner hair cell-auditory nerve synaptic junctions and the ascending auditory neuron. 
The other interesting aspect is in the nomenclature itself. A neuropathy usually refers to a disease of the peripheral nerve or nerves, but the auditory nerve itself is not always affected in Auditory Neuropathy Spectrum Disorder (ANSD). Also while the pure tone audiometry finding may vary from normal to near normal, there is consistent difficulty in perceiving speech in ANSD. 
Also referred to as auditory dyssynchrony, numerous risk factors reportedly associated and varying clinical presentation characterizing ANSD make the management options also as varied and controversial. Hearing aids and cochlear implants have been prescribed for ANSD with mixed outcome. Current effort is geared towards developing animal models that can precisely replicate findings in ANSD cases to assist further understanding and better management approach. 



References:
1. Auditory Neuropathy. Emedicine. http://emedicine.medscape.com/article/836769-overview 
2. Multi site diagnosis and managent of 260 patients with ANSD. http://csd.cbcs.usf.edu/an/Berlin_ANSD.pdf 

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