Auditory Neuropathy Spectrum Disorder (ANSD) encompasses what had previously been categorized as auditory neuropathy or auditory dyssynchrony. The broader term, ANSD, reflects multiple factors that can lead to a common, though sometimes variable, set of hearing and audiologic (hearing test) abnormalities.
ANSD is associated with poor word understanding relative to the level of hearing sound. Patients with ANSD have present otoacoustic emissions (OAE) but an absent or abnormal auditory evoked brainstem response (AEBR).
Otoacoustic emissions are measurable sounds produced by contractions of the hair cells in the cochlea. The presence of OAE indicates, physiologically, that the hair cells of the cochlea are functioning and the problem is between the hair cells and the brain. The AEBR is a measure of electrical activity arising in the cochlea, nerve of hearing and hearing centers in the brain. The abnormal AEBR seen in ANSD suggests that the pathways from the hair cells to the brain are, in fact, impaired.
ANSD occurs in approximately 10% of patients with profound sensorineural hearing loss. ANSD is being diagnosed more frequently in children due to newborn neonatal screening. Factors that predispose to ANSD include prematurity, low birth weight, hypoxia (low oxygen), and elevated bilirubin at birth. These children often perform much poorer with hearing aids than would be predicted by their hearing tests. While there is no curative treatment for ANSD, patients who perform poorly with hearing aids often receive a cochlear implant. Not unexpectedly, reflecting the variability in cause and site of the problem, some implanted patients do well and others do not perform well.