Audiological Profile in Auditory Neuropathy Spectrum Disorder – A Descriptive Study

Abstract

terms used to describe an auditory disorder seen in patients ranging in age from infants to adults. The prevalence of ANSD in deaf schoolchildren is 2.46% within the age range of 6–12 years. In children, they are detected by the presence of otoacoustic emissions (OAEs) in the absence of ABRs. In older age group, difficulty hearing in noise, fluctuating hearing, and speech perception performance not predict ed by the level of residual hearing have been reported. The multitude of etiologies for ANSD results in heterogeneous group of patients – making the management strategies even more challenging. The common etiologies put forward are – prematurity, neonatal insult, genetic abnormality, ototoxic drugs, and head injury.
Aim of the Study: This study aims to study the audiological profile in ANSD in a tertiary care hospital and to study the etiology of ANSD cases.
Materials and Methods: A total of 42 patients attending the ENT Outpatient Department of Government Medical College, Kozhikode, with ANSD were included in the study. An ethical committee clearance was obtained before the commencement of the study. An ethical committee cleared consent form was used for the study. All ANSD patients were evaluated with a detailed history including perinatal and development history, ototoxic drug exposure, head trauma, neurodegenerative conditions, and family history. Following clinical evaluation which included general examinations, ENT examination, and central nervous system examination, an audiological evaluation, which included pure tone audiometry, speech audiometry, immittance evaluation, OAE, and auditory brainstem response, was done. Radiological investigation (magnetic resonance imaging brain with inner ear – focusing on any structural anomalies; cochlea, vestibulocochlear nerve, and internal auditory canal) was done. Patients were counseled regarding the rehabilitation options based on their audiological and radiological results and the need for follow-up was explained.
Observation and Results: A total of 42 patients attending the ENT Outpatient Department (OPD) of Government Medical College, Kozhikode, with ANSD were included in the study. Among the 42 patients, 21 (50%) were in the age group of 11–20 years followed by 13 patients who were between 0 and 10 years (30.95%). The remaining 8 were aged above 20 years (19.04%). The youngest patient was 10 months old and the oldest was aged 38 years with a mean age of 10.35 ± 2.10 years. There were 29 (69.04%) females and 13 (30.95%) males. 3/42 (7.14%) patients gave a history of exposure to ototoxic drugs such as streptomycin, gentamicin, and kanamycin, but never had a history of loss of hearing before that. History of premature birth was noted in 10 (23.80%) patients and the remaining patients did not show premature birth history. Among the 42 patients of this study group, 23 (54.76%) had low birth weight, of which 2/42 (4.76%) were <1.5 kg. 21/42 (50%) patients had birth weight above 1.5 kg. 10/42 patients (23.80%) gave a history of neonatal intensive care unit (NICU) admissions at the time of their birth.
Conclusions: The major risk factor identified in this study for ANSD was low birth weight with prematurity, NICU admissions, and viral infections having significant contributions. On audiological evaluation, hearing loss was of mild-to-moderate range with a low-frequency loss. There was no statistical correlation between pure audiometry values and speech audiometry which was a characteristic observation. OAEs were present in the majority of patients with absent cochlear microphonics (reverse polarity) and acoustic reflexes.