The significance of hearing loss for children with Down syndrome

The first article in this issue provides readers with an account of hearing loss and hearing assessments, including a photocopiable audiogram (see pdf version), because we believe that the damaging effects of hearing loss are underestimated by many audiology and ENT specialists and that parents are not always given adequate detail when their child's hearing is assessed.

Hearing and spoken language

It may surprise readers to learn that the effect of hearing difficulties on spoken language development has been more difficult to demonstrate than might be expected. In many studies of the speech and language skills of children and teenagers with Down syndrome, hearing is measured on the same day as the tests of speech and language and usually hearing losses account for little of the variation seen in language skills. However, it may not be the hearing on the day - at the age of 7 or 13 years, for example - that explains speech and language profiles. It is more likely to be the hearing status of the child between birth and five years, at the time when language acquisition is usually rapid. To investigate the real impact of hearing at this stage we need to conduct longitudinal studies, following the same children over several years before school age.

This has been done by Jon Miller and researchers at the University of Wisconsin in the USA, but they did not find a significant effect of hearing loss on the children's progress. However, they point out that they only assessed hearing on the days when the children's speech and language was being monitored and, as conductive loss is a fluctuating condition, there is no way of knowing how well these children were hearing between the assessment visits.

Observations

In my view, based on working with babies and preschool children for many years, hearing loss due to middle ear 'glue' problems does play a significant part in delaying the spoken language progress of many preschoolers. Many parents report that they observe an immediate improvement in hearing following grommet operations - and often an obvious improvement in the child's attempts at sounds or words. We know that a number of factors are involved in the speech and language difficulties of our children, including verbal or phonological short-term memory difficulties and difficulties in producing speech sounds. (Phonology is the technical term for the speech sound system). It is possible that, because their short-term memory system for perceiving and storing speech sounds and words is impaired to some degree, the effects of mild hearing loss on their ability to hear and discriminate speech sounds is greater than it would be for a typical child.

Effects on speech

Miller and colleagues, in a recent review, suggest that the impact of hearing loss appears to be on children's phonological speech processing and speech production rather than on their word and sentence level understanding. This might be because the meanings of words and sentences in everyday contexts may be understood without hearing precisely every sound in the word - the general word sound pattern may be enough. However, in order to discriminate 'hat' from 'cat' or 'man' from 'van' - single sound discrimination becomes important and, if the child does not hear all sounds accurately, he or she has no stored information that is adequate for enabling them to copy or say speech sounds accurately.

Long term effects

I am also aware of the findings of studies such as those of Marcell and colleagues referred to in the article, which highlight the long term chronic effects of middle ear 'glue' - with 40% showing abnormal middle ear function as young adults. These young people had more difficulty with speech discrimination and language tasks at the time of the study and poorer language comprehension than those with good hearing - suggesting that their hearing loss had had a long term effect on their speech and language development and that it was continuing to impair their speech processing abilities on a daily basis.

I am not sure that all audiologists or ENT specialists realise that a mild hearing loss may have a greater impact on the speech and language development of a child with Down syndrome than for a typically developing child, because of their additional phonological memory and information processing difficulties. I am also not sure that all specialists realise that there is a risk of long-term middle ear damage from untreated 'glue' ear.

I would encourage all parents to ensure that the specialists involved with their children are aware of the specific risks of conductive hearing loss for children with Down syndrome and, if children have persistent 'glue' producing 40dB losses or more, I would recommend that parents ask to be referred to the hearing impaired service for the assistance of a teacher for the deaf, as parents have reported that this is usually very helpful.

Reference

1. Miller, J.F., Leddy, M. and Leavitt, L.A. (1999). (Eds). Improving the Communication of People with Down Syndrome. Baltimore: Paul Brookes Publishing.