Children with congenital unilateral sensorineural hearing loss : etiology, newborn diagnostics, and hearing aid amplification

Abstract: Congenital unilateral sensorineural hearing loss (uSNHL) comprises about 25% of the sensorineural hearing losses (SNHLs) found through newborn hearing screening (NHS) programs. Even if children with congenital uSNHL struggle in school and everyday listening situations, studies on etiology, hearing aid (HA) outcomes and intervention are few, so it is still unknown when and how intervention is optimally provided. The overall aim of the PhD project was to study the causes and mechanisms underlying congenital uSNHL and the effects of intervention. The four studies describe effects of HA amplification on pediatric congenital uSNHL (Study I), a basic research study of the transient-evoked otoacoustic emission (TEOAE, Study II), and causes for congenital uSNHL and affected auditory mechanisms (Studies III and IV). In Study I six school-aged children with congenital uNSHL were studied. They all had HA experience and were fitted with HAs late in development. Outcomes showed both HA benefit and dis-benefit. HA benefit was found in one-to-one communication, whereas dis-benefit was found for sound localization accuracy. A close relationship was found between aided sound localization and neural maturation. In Study II neonatal TEOAE heredity was studied in 454 twins, showing that TEOAE levels are largely inherited. Neonatal female twins with male co-twins did not show masculinized (i.e., reduced) TEOAE levels, contrary to the twin testosterone transfer hypothesis proposed previously based on young adult twin’s OAEs. Studies III and IV investigated etiology in 20 infants with congenital uSNHL, consecutively recruited from the newborn hearing screening (NHS) program in Region Stockholm. Malformations were found in 64% of the 14 infants tested with imaging, 50% showed no cochlear nerve on the impaired side, and 29% showed inner ear malformations. All 20 infants tested negative for congenital cytomegalovirus (cCMV) infection. The interaural acoustic reflex threshold and auditory brainstem response (ABR) results indicated a lack of loudness recruitment. Of the 18 infants that were genetically tested, 28% received a genetic diagnosis. All three infants with comorbidities observed at birth received a genetic diagnosis, whereas 13% (n = 2/15) of the infants without comorbidities observed at birth received a genetic diagnosis. The overall results indicate that congenital uSNHL is different from bilateral SNHL, with many malformations, different auditory mechanisms, and a less explored genetic workup. Based on the results we recommend imaging for all congenital uSNHL, and genetic testing for alleged syndromic congenital uSNHL, due to high diagnostic yields. Late-fitted HAs can give both benefits and dis-benefits to school-aged children depending on the listening situation. Finally, HAs may be more efficient if loudness recruitment differences may be taken into account in the HA fitting to children with congenital uSNHL, and if HAs were fitted earlier in development, although this needs to be specifically evaluated in future research.