Investigation of the child with permanent hearing impairment

In England the birth prevalence of bilateral per manent childhood hearing impairment (PCHI) of >40 dB HL is approximately 1:1000 live births but almost doubles up to the age of 9 years.1 The latter is accounted for by cases of PCHI that were not screened as part of the Newborn Hearing Screening Programme (NHSP) or were false nega tives, as well as children with acquired hearing loss and those with late onset or progressive deafness. In some areas the prevalence can be two to three times this figure.2 About 40% of children with PCHI have additional health or developmental problems, and about 20% of this population have more than two problems.3 In the developed world, at least 50% of PCHI has a genetic aetiology with environmental causes (which may include adverse perinatal factors, for example, extreme prematurity, hyperbilirubinaemia, aminoglycoside drugs, hypoxia, meningitis and congenital infections) and head trauma accounting for a further 25%. In the remaining 25% no cause for the deafness is found following aetiological investigation.4 A number of events have influenced how and when the aetiology of PCHI should be investigated. These include the introduction of the NHSP and its quality assessment programme which includes a standard that relates to implementation of best practice in aetiological investigation of deafness. Each local NHSP screening site has a lead clinician who is responsible for the aetiological investigation.5 Training for lead clinicians in aetiological investigation is provided by the NHSP. Advances in the field of molecular genetics have also had a major impact which will continue in the future with “next generation” sequencing technologies. Advances in inner ear imaging techniques have also contributed significantly to aetiological investigation of many cases of PCHI. Research into the contribution of both symptomatic and asymptomatic cytomegalovirus (CMV) infection to PCHI …