Medical evaluation of pediatric hearing loss - Laboratory, radiographic, and genetic testing

The change in the relative incidence of acquired versus hereditary causes of pediatric hearing loss reflects two important advances. First, this change is a reflection of improved neonatal care and universal immunization programs. The latter are typified by the vaccination program for congenital rubella, which has almost completely eliminated this disease in the Western World, and the vaccination program for Haemophilus influenza type B, which has reduced the incidence of hearing loss from meningitis. The decrease in acquired hearing loss has resulted in a relative increase in hereditary (genetic) hearing loss. Second, as our understanding of the genetics of hearing loss has advanced during the past few years, we have been able to identify previously undiagnosed cases of hereditary hearing loss definitely on the basis of specific genetic testing. Pediatric hearing loss may be classified as prelingual (congenital) or postlingual (late onset). Prevalence estimates of congenital and early pediatric hearing loss vary and, in many cases, are underestimated. Figures based on universal neonatal screening programs are perhaps the most accurate. Mason and Herrmann have reported bilateral hearing loss >35 dB in 1.4:1000 live births in Hawaii [1]; other U.S. studies have shown rates of 2.2:1000 and 3:1000 live births, respectively [2,3]. European rates, mainly obtained from retrospective studies, are similar with ranges between 1.4 and 2.1:1000 live births [4-6]. In excess of 50% of these cases are estimated to be genetic, 25% acquired, and 25% of unknown etiology [7]. Approximately 75-80% of genetic deafness is inherited in an autosomal recessive fashion, 15-20% in an autosomal dominant fashion, and 1-2% in an X-linked fashion; a few exhibit mitochondrial (maternal) inheritance. Neonatal hearing screening may not identify children with progressive hearing loss, which accounts for 15-20% of preschool children with sensorineural hearing loss (SNHL). When these children and those with late onset hearing loss are taken into account, the overall incidence of pediatric SNHL is probably 50% higher than the figures quoted above. This article outlines the medical evaluation of pediatric SNHL. We examine the role of laboratory and radiographic investigations and explore in detail the genetic tests available and their implications.