Auditory Neuropathy Spectrum Disorder

Hearing test mismatch: hair cells work, nerve transmission fails

Overview

In auditory neuropathy spectrum disorder, ANSD, the outer hair cells of the cochlea respond normally to sound, so otoacoustic emissions or a cochlear microphonic are present, but transmission through the inner hair cells, their synapses, or the auditory nerve is disordered and unsynchronized. As a result the auditory brainstem response is absent or severely abnormal. Speech understanding is often disproportionately poor, especially in noise, and can be much worse than the audiogram suggests, while hearing thresholds themselves range from normal to profound and may fluctuate. Risk factors include prematurity, severe neonatal jaundice, lack of oxygen at birth, and genetic causes such as variants in the OTOF gene, which encodes otoferlin. Some infants show improvement over time, complicating early decisions. Hearing aids give variable benefit, while cochlear implants, which stimulate the nerve directly, can work well in some forms, particularly those originating at the synapse.