CURRENT TOPIC Hearing impairment after bacterial meningitis : a review

Postmeningitic hearing impairment is an important public health problem with implications for both paediatric and audiology services. A recent population study has shown that, by the age of 3 years, the proportion of children with a known bilateral profound hearing impairment who have an acquired impairment is approximately 20%. Of these acquired impairments, 90% are probably due to bacterial meningitis.' Furthermore, studies of cohorts of children born in the 1970s and early 1980s indicate that 6% of all childhood hearing impairment is due to bacterial meningitis.2 3 Not all children surviving bacterial meningitis suffer permanent sensorineural hearing impairment. How many do, and why are certain children affected but not others? Are there any factors within the illness, within the children, or within the medical treatment that could predict the children at greatest risk? This article reviews the recent literature as a source of answers to these questions and recommends management guidelines in the light of current knowledge of the pathology. (Except where otherwise stated, 'impairment' in this article refers to sensonrneural hearing impairment, that is permanently raised hearing thresholds and loss of other auditory functions such as frequency resolution, due to damage to the eighth nerve or to the receptor cells of the inner ear.) Total loss of hearing disrupts the development of communication skills, particularly in young children who have not fully developed speech and language. It can also lead to regression to an earlier stage.4 This disruption is an important sequela of bacterial meningitis, justifying the effort ofearly identification to enable appropriate habilitation to begin as soon as possible. Partial hearing impairment and/or unilateral losses also occur9"I and also need to be identified with minimal delay, because these children may also suffer auditory and linguistic disabilities that are only subtly symptomatic. Such children often display behavioural compensations and may appear to hear normally. Unaware of what he is missing, a young child will not complain. Crucial stimulation may be missed," which is particularly important at school entry. Parents and teachers should be aware of any degree of impairment, even if it is too mild for hearing aids to be beneficial. Bacterial meningitis may also cause more widespread damage. If a child is left with multiple handicaps, any hearing impairment is more easily overlooked and difficult to detect. In such 2hildren assisting any impairment to hearing may be of even greater benefit than in less complex cases.